Merge branch 'master' into sync-from-rust

crates/hir-def/src/attr.rs

@@ -5,7 +5,7 @@ pub mod builtin;
 #[cfg(test)]
 mod tests;
 
-use std::{hash::Hash, ops};
+use std::{hash::Hash, ops, slice::Iter as SliceIter};
 
 use base_db::CrateId;
 use cfg::{CfgExpr, CfgOptions};
@@ -14,12 +14,11 @@ use hir_expand::{
     attrs::{collect_attrs, Attr, AttrId, RawAttrs},
     HirFileId, InFile,
 };
-use itertools::Itertools;
 use la_arena::{ArenaMap, Idx, RawIdx};
 use mbe::DelimiterKind;
 use syntax::{
-    ast::{self, HasAttrs, IsString},
-    AstPtr, AstToken, SmolStr, TextRange, TextSize,
+    ast::{self, HasAttrs},
+    AstPtr, SmolStr,
 };
 use triomphe::Arc;
 
@@ -33,26 +32,6 @@ use crate::{
     LocalFieldId, Lookup, MacroId, VariantId,
 };
 
-/// Holds documentation
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct Documentation(String);
-
-impl Documentation {
-    pub fn new(s: String) -> Self {
-        Documentation(s)
-    }
-
-    pub fn as_str(&self) -> &str {
-        &self.0
-    }
-}
-
-impl From<Documentation> for String {
-    fn from(Documentation(string): Documentation) -> Self {
-        string
-    }
-}
-
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
 pub struct Attrs(RawAttrs);
 
@@ -221,33 +200,6 @@ impl Attrs {
         self.by_key("lang").string_value().and_then(|it| LangItem::from_str(it))
     }
 
-    pub fn docs(&self) -> Option<Documentation> {
-        let docs = self.by_key("doc").attrs().filter_map(|attr| attr.string_value());
-        let indent = doc_indent(self);
-        let mut buf = String::new();
-        for doc in docs {
-            // str::lines doesn't yield anything for the empty string
-            if !doc.is_empty() {
-                buf.extend(Itertools::intersperse(
-                    doc.lines().map(|line| {
-                        line.char_indices()
-                            .nth(indent)
-                            .map_or(line, |(offset, _)| &line[offset..])
-                            .trim_end()
-                    }),
-                    "\n",
-                ));
-            }
-            buf.push('\n');
-        }
-        buf.pop();
-        if buf.is_empty() {
-            None
-        } else {
-            Some(Documentation(buf))
-        }
-    }
-
     pub fn has_doc_hidden(&self) -> bool {
         self.by_key("doc").tt_values().any(|tt| {
             tt.delimiter.kind == DelimiterKind::Parenthesis &&
@@ -299,7 +251,6 @@ impl Attrs {
     }
 }
 
-use std::slice::Iter as SliceIter;
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd)]
 pub enum DocAtom {
     /// eg. `#[doc(hidden)]`
@@ -313,7 +264,6 @@ pub enum DocAtom {
 
 // Adapted from `CfgExpr` parsing code
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-// #[cfg_attr(test, derive(derive_arbitrary::Arbitrary))]
 pub enum DocExpr {
     Invalid,
     /// eg. `#[doc(hidden)]`, `#[doc(alias = "x")]`
@@ -574,62 +524,6 @@ impl AttrsWithOwner {
 
         AttrSourceMap::new(owner.as_ref().map(|node| node as &dyn HasAttrs))
     }
-
-    pub fn docs_with_rangemap(
-        &self,
-        db: &dyn DefDatabase,
-    ) -> Option<(Documentation, DocsRangeMap)> {
-        let docs =
-            self.by_key("doc").attrs().filter_map(|attr| attr.string_value().map(|s| (s, attr.id)));
-        let indent = doc_indent(self);
-        let mut buf = String::new();
-        let mut mapping = Vec::new();
-        for (doc, idx) in docs {
-            if !doc.is_empty() {
-                let mut base_offset = 0;
-                for raw_line in doc.split('\n') {
-                    let line = raw_line.trim_end();
-                    let line_len = line.len();
-                    let (offset, line) = match line.char_indices().nth(indent) {
-                        Some((offset, _)) => (offset, &line[offset..]),
-                        None => (0, line),
-                    };
-                    let buf_offset = buf.len();
-                    buf.push_str(line);
-                    mapping.push((
-                        TextRange::new(buf_offset.try_into().ok()?, buf.len().try_into().ok()?),
-                        idx,
-                        TextRange::at(
-                            (base_offset + offset).try_into().ok()?,
-                            line_len.try_into().ok()?,
-                        ),
-                    ));
-                    buf.push('\n');
-                    base_offset += raw_line.len() + 1;
-                }
-            } else {
-                buf.push('\n');
-            }
-        }
-        buf.pop();
-        if buf.is_empty() {
-            None
-        } else {
-            Some((Documentation(buf), DocsRangeMap { mapping, source_map: self.source_map(db) }))
-        }
-    }
-}
-
-fn doc_indent(attrs: &Attrs) -> usize {
-    attrs
-        .by_key("doc")
-        .attrs()
-        .filter_map(|attr| attr.string_value())
-        .flat_map(|s| s.lines())
-        .filter(|line| !line.chars().all(|c| c.is_whitespace()))
-        .map(|line| line.chars().take_while(|c| c.is_whitespace()).count())
-        .min()
-        .unwrap_or(0)
 }
 
 #[derive(Debug)]
@@ -673,7 +567,7 @@ impl AttrSourceMap {
         self.source_of_id(attr.id)
     }
 
-    fn source_of_id(&self, id: AttrId) -> InFile<&Either<ast::Attr, ast::Comment>> {
+    pub fn source_of_id(&self, id: AttrId) -> InFile<&Either<ast::Attr, ast::Comment>> {
         let ast_idx = id.ast_index();
         let file_id = match self.mod_def_site_file_id {
             Some((file_id, def_site_cut)) if def_site_cut <= ast_idx => file_id,
@@ -687,69 +581,6 @@ impl AttrSourceMap {
     }
 }
 
-/// A struct to map text ranges from [`Documentation`] back to TextRanges in the syntax tree.
-#[derive(Debug)]
-pub struct DocsRangeMap {
-    source_map: AttrSourceMap,
-    // (docstring-line-range, attr_index, attr-string-range)
-    // a mapping from the text range of a line of the [`Documentation`] to the attribute index and
-    // the original (untrimmed) syntax doc line
-    mapping: Vec<(TextRange, AttrId, TextRange)>,
-}
-
-impl DocsRangeMap {
-    /// Maps a [`TextRange`] relative to the documentation string back to its AST range
-    pub fn map(&self, range: TextRange) -> Option<InFile<TextRange>> {
-        let found = self.mapping.binary_search_by(|(probe, ..)| probe.ordering(range)).ok()?;
-        let (line_docs_range, idx, original_line_src_range) = self.mapping[found];
-        if !line_docs_range.contains_range(range) {
-            return None;
-        }
-
-        let relative_range = range - line_docs_range.start();
-
-        let InFile { file_id, value: source } = self.source_map.source_of_id(idx);
-        match source {
-            Either::Left(attr) => {
-                let string = get_doc_string_in_attr(attr)?;
-                let text_range = string.open_quote_text_range()?;
-                let range = TextRange::at(
-                    text_range.end() + original_line_src_range.start() + relative_range.start(),
-                    string.syntax().text_range().len().min(range.len()),
-                );
-                Some(InFile { file_id, value: range })
-            }
-            Either::Right(comment) => {
-                let text_range = comment.syntax().text_range();
-                let range = TextRange::at(
-                    text_range.start()
-                        + TextSize::try_from(comment.prefix().len()).ok()?
-                        + original_line_src_range.start()
-                        + relative_range.start(),
-                    text_range.len().min(range.len()),
-                );
-                Some(InFile { file_id, value: range })
-            }
-        }
-    }
-}
-
-fn get_doc_string_in_attr(it: &ast::Attr) -> Option<ast::String> {
-    match it.expr() {
-        // #[doc = lit]
-        Some(ast::Expr::Literal(lit)) => match lit.kind() {
-            ast::LiteralKind::String(it) => Some(it),
-            _ => None,
-        },
-        // #[cfg_attr(..., doc = "", ...)]
-        None => {
-            // FIXME: See highlight injection for what to do here
-            None
-        }
-        _ => None,
-    }
-}
-
 #[derive(Debug, Clone, Copy)]
 pub struct AttrQuery<'attr> {
     attrs: &'attr Attrs,

crates/hir-def/src/attr/builtin.rs

@@ -8,7 +8,8 @@
 //! name resolution, and `BUILTIN_ATTRIBUTES` is almost entirely unchanged from the original, to
 //! ease updating.
 
-use once_cell::sync::OnceCell;
+use std::sync::OnceLock;
+
 use rustc_hash::FxHashMap;
 
 /// Ignored attribute namespaces used by tools.
@@ -29,7 +30,7 @@ pub struct AttributeTemplate {
 }
 
 pub fn find_builtin_attr_idx(name: &str) -> Option<usize> {
-    static BUILTIN_LOOKUP_TABLE: OnceCell<FxHashMap<&'static str, usize>> = OnceCell::new();
+    static BUILTIN_LOOKUP_TABLE: OnceLock<FxHashMap<&'static str, usize>> = OnceLock::new();
     BUILTIN_LOOKUP_TABLE
         .get_or_init(|| {
             INERT_ATTRIBUTES.iter().map(|attr| attr.name).enumerate().map(|(a, b)| (b, a)).collect()

crates/hir-def/src/body.rs

@@ -65,6 +65,8 @@ pub type LabelSource = InFile<LabelPtr>;
 
 pub type FieldPtr = AstPtr<ast::RecordExprField>;
 pub type FieldSource = InFile<FieldPtr>;
+pub type PatFieldPtr = AstPtr<ast::RecordPatField>;
+pub type PatFieldSource = InFile<PatFieldPtr>;
 
 /// An item body together with the mapping from syntax nodes to HIR expression
 /// IDs. This is needed to go from e.g. a position in a file to the HIR
@@ -90,8 +92,8 @@ pub struct BodySourceMap {
 
     /// We don't create explicit nodes for record fields (`S { record_field: 92 }`).
     /// Instead, we use id of expression (`92`) to identify the field.
-    field_map: FxHashMap<FieldSource, ExprId>,
     field_map_back: FxHashMap<ExprId, FieldSource>,
+    pat_field_map_back: FxHashMap<PatId, PatFieldSource>,
 
     expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
 
@@ -164,9 +166,10 @@ impl Body {
         };
         let module = def.module(db);
         let expander = Expander::new(db, file_id, module);
-        let (mut body, source_map) =
+        let (mut body, mut source_map) =
             Body::new(db, def, expander, params, body, module.krate, is_async_fn);
         body.shrink_to_fit();
+        source_map.shrink_to_fit();
 
         (Arc::new(body), Arc::new(source_map))
     }
@@ -375,9 +378,8 @@ impl BodySourceMap {
         self.field_map_back[&expr].clone()
     }
 
-    pub fn node_field(&self, node: InFile<&ast::RecordExprField>) -> Option<ExprId> {
-        let src = node.map(AstPtr::new);
-        self.field_map.get(&src).cloned()
+    pub fn pat_field_syntax(&self, pat: PatId) -> PatFieldSource {
+        self.pat_field_map_back[&pat].clone()
     }
 
     pub fn macro_expansion_expr(&self, node: InFile<&ast::MacroExpr>) -> Option<ExprId> {
@@ -389,4 +391,29 @@ impl BodySourceMap {
     pub fn diagnostics(&self) -> &[BodyDiagnostic] {
         &self.diagnostics
     }
+
+    fn shrink_to_fit(&mut self) {
+        let Self {
+            expr_map,
+            expr_map_back,
+            pat_map,
+            pat_map_back,
+            label_map,
+            label_map_back,
+            field_map_back,
+            pat_field_map_back,
+            expansions,
+            diagnostics,
+        } = self;
+        expr_map.shrink_to_fit();
+        expr_map_back.shrink_to_fit();
+        pat_map.shrink_to_fit();
+        pat_map_back.shrink_to_fit();
+        label_map.shrink_to_fit();
+        label_map_back.shrink_to_fit();
+        field_map_back.shrink_to_fit();
+        pat_field_map_back.shrink_to_fit();
+        expansions.shrink_to_fit();
+        diagnostics.shrink_to_fit();
+    }
 }

crates/hir-def/src/body/lower.rs

@@ -25,13 +25,20 @@ use triomphe::Arc;
 
 use crate::{
     body::{Body, BodyDiagnostic, BodySourceMap, ExprPtr, LabelPtr, PatPtr},
+    builtin_type::BuiltinUint,
     data::adt::StructKind,
     db::DefDatabase,
     expander::Expander,
     hir::{
-        dummy_expr_id, Array, Binding, BindingAnnotation, BindingId, BindingProblems, CaptureBy,
-        ClosureKind, Expr, ExprId, Label, LabelId, Literal, LiteralOrConst, MatchArm, Movability,
-        Pat, PatId, RecordFieldPat, RecordLitField, Statement,
+        dummy_expr_id,
+        format_args::{
+            self, FormatAlignment, FormatArgs, FormatArgsPiece, FormatArgument, FormatArgumentKind,
+            FormatArgumentsCollector, FormatCount, FormatDebugHex, FormatOptions,
+            FormatPlaceholder, FormatSign, FormatTrait,
+        },
+        Array, Binding, BindingAnnotation, BindingId, BindingProblems, CaptureBy, ClosureKind,
+        Expr, ExprId, InlineAsm, Label, LabelId, Literal, LiteralOrConst, MatchArm, Movability,
+        OffsetOf, Pat, PatId, RecordFieldPat, RecordLitField, Statement,
     },
     item_scope::BuiltinShadowMode,
     lang_item::LangItem,
@@ -42,6 +49,8 @@ use crate::{
     AdtId, BlockId, BlockLoc, ConstBlockLoc, DefWithBodyId, ModuleDefId, UnresolvedMacro,
 };
 
+type FxIndexSet<K> = indexmap::IndexSet<K, std::hash::BuildHasherDefault<rustc_hash::FxHasher>>;
+
 pub(super) fn lower(
     db: &dyn DefDatabase,
     owner: DefWithBodyId,
@@ -437,7 +446,6 @@ impl ExprCollector<'_> {
                                 None => self.missing_expr(),
                             };
                             let src = self.expander.to_source(AstPtr::new(&field));
-                            self.source_map.field_map.insert(src.clone(), expr);
                             self.source_map.field_map_back.insert(expr, src);
                             Some(RecordLitField { name, expr })
                         })
@@ -579,11 +587,6 @@ impl ExprCollector<'_> {
                     syntax_ptr,
                 )
             }
-            ast::Expr::BoxExpr(e) => {
-                let expr = self.collect_expr_opt(e.expr());
-                self.alloc_expr(Expr::Box { expr }, syntax_ptr)
-            }
-
             ast::Expr::ArrayExpr(e) => {
                 let kind = e.kind();
 
@@ -653,6 +656,16 @@ impl ExprCollector<'_> {
                 }
             }
             ast::Expr::UnderscoreExpr(_) => self.alloc_expr(Expr::Underscore, syntax_ptr),
+            ast::Expr::AsmExpr(e) => {
+                let e = self.collect_expr_opt(e.expr());
+                self.alloc_expr(Expr::InlineAsm(InlineAsm { e }), syntax_ptr)
+            }
+            ast::Expr::OffsetOfExpr(e) => {
+                let container = Interned::new(TypeRef::from_ast_opt(&self.ctx(), e.ty()));
+                let fields = e.fields().map(|it| it.as_name()).collect();
+                self.alloc_expr(Expr::OffsetOf(OffsetOf { container, fields }), syntax_ptr)
+            }
+            ast::Expr::FormatArgsExpr(f) => self.collect_format_args(f, syntax_ptr),
         })
     }
 
@@ -663,6 +676,7 @@ impl ExprCollector<'_> {
         let result_expr_id = self.alloc_expr(Expr::Missing, syntax_ptr);
         let prev_binding_owner = self.current_binding_owner.take();
         self.current_binding_owner = Some(result_expr_id);
+
         (result_expr_id, prev_binding_owner)
     }
 
@@ -744,7 +758,27 @@ impl ExprCollector<'_> {
     fn collect_while_loop(&mut self, syntax_ptr: AstPtr<ast::Expr>, e: ast::WhileExpr) -> ExprId {
         let label = e.label().map(|label| self.collect_label(label));
         let body = self.collect_labelled_block_opt(label, e.loop_body());
-        let condition = self.collect_expr_opt(e.condition());
+
+        // Labels can also be used in the condition expression, like this:
+        // ```
+        // fn main() {
+        //     let mut optional = Some(0);
+        //     'my_label: while let Some(a) = match optional {
+        //         None => break 'my_label,
+        //         Some(val) => Some(val),
+        //     } {
+        //         println!("{}", a);
+        //         optional = None;
+        //     }
+        // }
+        // ```
+        let condition = match label {
+            Some(label) => {
+                self.with_labeled_rib(label, |this| this.collect_expr_opt(e.condition()))
+            }
+            None => self.collect_expr_opt(e.condition()),
+        };
+
         let break_expr =
             self.alloc_expr(Expr::Break { expr: None, label: None }, syntax_ptr.clone());
         let if_expr = self.alloc_expr(
@@ -1295,23 +1329,21 @@ impl ExprCollector<'_> {
             ast::Pat::RecordPat(p) => {
                 let path =
                     p.path().and_then(|path| self.expander.parse_path(self.db, path)).map(Box::new);
-                let args = p
-                    .record_pat_field_list()
-                    .expect("every struct should have a field list")
+                let record_pat_field_list =
+                    &p.record_pat_field_list().expect("every struct should have a field list");
+                let args = record_pat_field_list
                     .fields()
                     .filter_map(|f| {
                         let ast_pat = f.pat()?;
                         let pat = self.collect_pat(ast_pat, binding_list);
                         let name = f.field_name()?.as_name();
+                        let src = self.expander.to_source(AstPtr::new(&f));
+                        self.source_map.pat_field_map_back.insert(pat, src);
                         Some(RecordFieldPat { name, pat })
                     })
                     .collect();
 
-                let ellipsis = p
-                    .record_pat_field_list()
-                    .expect("every struct should have a field list")
-                    .rest_pat()
-                    .is_some();
+                let ellipsis = record_pat_field_list.rest_pat().is_some();
 
                 Pat::Record { path, args, ellipsis }
             }
@@ -1531,6 +1563,401 @@ impl ExprCollector<'_> {
         }
     }
     // endregion: labels
+
+    // region: format
+    fn expand_macros_to_string(&mut self, expr: ast::Expr) -> Option<(ast::String, bool)> {
+        let m = match expr {
+            ast::Expr::MacroExpr(m) => m,
+            ast::Expr::Literal(l) => {
+                return match l.kind() {
+                    ast::LiteralKind::String(s) => Some((s, true)),
+                    _ => None,
+                }
+            }
+            _ => return None,
+        };
+        let e = m.macro_call()?;
+        let macro_ptr = AstPtr::new(&e);
+        let (exp, _) = self.collect_macro_call(e, macro_ptr, true, |this, expansion| {
+            expansion.and_then(|it| this.expand_macros_to_string(it))
+        })?;
+        Some((exp, false))
+    }
+
+    fn collect_format_args(
+        &mut self,
+        f: ast::FormatArgsExpr,
+        syntax_ptr: AstPtr<ast::Expr>,
+    ) -> ExprId {
+        let mut args = FormatArgumentsCollector::new();
+        f.args().for_each(|arg| {
+            args.add(FormatArgument {
+                kind: match arg.name() {
+                    Some(name) => FormatArgumentKind::Named(name.as_name()),
+                    None => FormatArgumentKind::Normal,
+                },
+                expr: self.collect_expr_opt(arg.expr()),
+            });
+        });
+        let template = f.template();
+        let fmt_snippet = template.as_ref().map(ToString::to_string);
+        let fmt = match template.and_then(|it| self.expand_macros_to_string(it)) {
+            Some((s, is_direct_literal)) => {
+                format_args::parse(&s, fmt_snippet, args, is_direct_literal, |name| {
+                    self.alloc_expr_desugared(Expr::Path(Path::from(name)))
+                })
+            }
+            None => FormatArgs { template: Default::default(), arguments: args.finish() },
+        };
+
+        // Create a list of all _unique_ (argument, format trait) combinations.
+        // E.g. "{0} {0:x} {0} {1}" -> [(0, Display), (0, LowerHex), (1, Display)]
+        let mut argmap = FxIndexSet::default();
+        for piece in fmt.template.iter() {
+            let FormatArgsPiece::Placeholder(placeholder) = piece else { continue };
+            if let Ok(index) = placeholder.argument.index {
+                argmap.insert((index, ArgumentType::Format(placeholder.format_trait)));
+            }
+        }
+
+        let lit_pieces =
+            fmt.template
+                .iter()
+                .enumerate()
+                .filter_map(|(i, piece)| {
+                    match piece {
+                        FormatArgsPiece::Literal(s) => Some(
+                            self.alloc_expr_desugared(Expr::Literal(Literal::String(s.clone()))),
+                        ),
+                        &FormatArgsPiece::Placeholder(_) => {
+                            // Inject empty string before placeholders when not already preceded by a literal piece.
+                            if i == 0
+                                || matches!(fmt.template[i - 1], FormatArgsPiece::Placeholder(_))
+                            {
+                                Some(self.alloc_expr_desugared(Expr::Literal(Literal::String(
+                                    "".into(),
+                                ))))
+                            } else {
+                                None
+                            }
+                        }
+                    }
+                })
+                .collect();
+        let lit_pieces = self.alloc_expr_desugared(Expr::Array(Array::ElementList {
+            elements: lit_pieces,
+            is_assignee_expr: false,
+        }));
+        let lit_pieces = self.alloc_expr_desugared(Expr::Ref {
+            expr: lit_pieces,
+            rawness: Rawness::Ref,
+            mutability: Mutability::Shared,
+        });
+        let format_options = {
+            // Generate:
+            //     &[format_spec_0, format_spec_1, format_spec_2]
+            let elements = fmt
+                .template
+                .iter()
+                .filter_map(|piece| {
+                    let FormatArgsPiece::Placeholder(placeholder) = piece else { return None };
+                    Some(self.make_format_spec(placeholder, &mut argmap))
+                })
+                .collect();
+            let array = self.alloc_expr_desugared(Expr::Array(Array::ElementList {
+                elements,
+                is_assignee_expr: false,
+            }));
+            self.alloc_expr_desugared(Expr::Ref {
+                expr: array,
+                rawness: Rawness::Ref,
+                mutability: Mutability::Shared,
+            })
+        };
+        let arguments = &*fmt.arguments.arguments;
+
+        let args = if arguments.is_empty() {
+            let expr = self.alloc_expr_desugared(Expr::Array(Array::ElementList {
+                elements: Box::default(),
+                is_assignee_expr: false,
+            }));
+            self.alloc_expr_desugared(Expr::Ref {
+                expr,
+                rawness: Rawness::Ref,
+                mutability: Mutability::Shared,
+            })
+        } else {
+            // Generate:
+            //     &match (&arg0, &arg1, &…) {
+            //         args => [
+            //             <core::fmt::Argument>::new_display(args.0),
+            //             <core::fmt::Argument>::new_lower_hex(args.1),
+            //             <core::fmt::Argument>::new_debug(args.0),
+            //             …
+            //         ]
+            //     }
+            let args = argmap
+                .iter()
+                .map(|&(arg_index, ty)| {
+                    let arg = self.alloc_expr_desugared(Expr::Ref {
+                        expr: arguments[arg_index].expr,
+                        rawness: Rawness::Ref,
+                        mutability: Mutability::Shared,
+                    });
+                    self.make_argument(arg, ty)
+                })
+                .collect();
+            let array = self.alloc_expr_desugared(Expr::Array(Array::ElementList {
+                elements: args,
+                is_assignee_expr: false,
+            }));
+            self.alloc_expr_desugared(Expr::Ref {
+                expr: array,
+                rawness: Rawness::Ref,
+                mutability: Mutability::Shared,
+            })
+        };
+
+        // Generate:
+        //     <core::fmt::Arguments>::new_v1_formatted(
+        //         lit_pieces,
+        //         args,
+        //         format_options,
+        //         unsafe { ::core::fmt::UnsafeArg::new() }
+        //     )
+
+        let Some(new_v1_formatted) =
+            LangItem::FormatArguments.ty_rel_path(self.db, self.krate, name![new_v1_formatted])
+        else {
+            return self.missing_expr();
+        };
+        let Some(unsafe_arg_new) =
+            LangItem::FormatUnsafeArg.ty_rel_path(self.db, self.krate, name![new])
+        else {
+            return self.missing_expr();
+        };
+        let new_v1_formatted = self.alloc_expr_desugared(Expr::Path(new_v1_formatted));
+
+        let unsafe_arg_new = self.alloc_expr_desugared(Expr::Path(unsafe_arg_new));
+        let unsafe_arg_new = self.alloc_expr_desugared(Expr::Call {
+            callee: unsafe_arg_new,
+            args: Box::default(),
+            is_assignee_expr: false,
+        });
+        let unsafe_arg_new = self.alloc_expr_desugared(Expr::Unsafe {
+            id: None,
+            statements: Box::default(),
+            tail: Some(unsafe_arg_new),
+        });
+
+        self.alloc_expr(
+            Expr::Call {
+                callee: new_v1_formatted,
+                args: Box::new([lit_pieces, args, format_options, unsafe_arg_new]),
+                is_assignee_expr: false,
+            },
+            syntax_ptr,
+        )
+    }
+
+    /// Generate a hir expression for a format_args placeholder specification.
+    ///
+    /// Generates
+    ///
+    /// ```text
+    ///     <core::fmt::rt::Placeholder::new(
+    ///         …usize, // position
+    ///         '…', // fill
+    ///         <core::fmt::rt::Alignment>::…, // alignment
+    ///         …u32, // flags
+    ///         <core::fmt::rt::Count::…>, // width
+    ///         <core::fmt::rt::Count::…>, // precision
+    ///     )
+    /// ```
+    fn make_format_spec(
+        &mut self,
+        placeholder: &FormatPlaceholder,
+        argmap: &mut FxIndexSet<(usize, ArgumentType)>,
+    ) -> ExprId {
+        let position = match placeholder.argument.index {
+            Ok(arg_index) => {
+                let (i, _) =
+                    argmap.insert_full((arg_index, ArgumentType::Format(placeholder.format_trait)));
+                self.alloc_expr_desugared(Expr::Literal(Literal::Uint(
+                    i as u128,
+                    Some(BuiltinUint::Usize),
+                )))
+            }
+            Err(_) => self.missing_expr(),
+        };
+        let &FormatOptions {
+            ref width,
+            ref precision,
+            alignment,
+            fill,
+            sign,
+            alternate,
+            zero_pad,
+            debug_hex,
+        } = &placeholder.format_options;
+        let fill = self.alloc_expr_desugared(Expr::Literal(Literal::Char(fill.unwrap_or(' '))));
+
+        let align = {
+            let align = LangItem::FormatAlignment.ty_rel_path(
+                self.db,
+                self.krate,
+                match alignment {
+                    Some(FormatAlignment::Left) => name![Left],
+                    Some(FormatAlignment::Right) => name![Right],
+                    Some(FormatAlignment::Center) => name![Center],
+                    None => name![Unknown],
+                },
+            );
+            match align {
+                Some(path) => self.alloc_expr_desugared(Expr::Path(path)),
+                None => self.missing_expr(),
+            }
+        };
+        // This needs to match `Flag` in library/core/src/fmt/rt.rs.
+        let flags: u32 = ((sign == Some(FormatSign::Plus)) as u32)
+            | ((sign == Some(FormatSign::Minus)) as u32) << 1
+            | (alternate as u32) << 2
+            | (zero_pad as u32) << 3
+            | ((debug_hex == Some(FormatDebugHex::Lower)) as u32) << 4
+            | ((debug_hex == Some(FormatDebugHex::Upper)) as u32) << 5;
+        let flags = self.alloc_expr_desugared(Expr::Literal(Literal::Uint(
+            flags as u128,
+            Some(BuiltinUint::U32),
+        )));
+        let precision = self.make_count(&precision, argmap);
+        let width = self.make_count(&width, argmap);
+
+        let format_placeholder_new = {
+            let format_placeholder_new =
+                LangItem::FormatPlaceholder.ty_rel_path(self.db, self.krate, name![new]);
+            match format_placeholder_new {
+                Some(path) => self.alloc_expr_desugared(Expr::Path(path)),
+                None => self.missing_expr(),
+            }
+        };
+
+        self.alloc_expr_desugared(Expr::Call {
+            callee: format_placeholder_new,
+            args: Box::new([position, fill, align, flags, precision, width]),
+            is_assignee_expr: false,
+        })
+    }
+
+    /// Generate a hir expression for a format_args Count.
+    ///
+    /// Generates:
+    ///
+    /// ```text
+    ///     <core::fmt::rt::Count>::Is(…)
+    /// ```
+    ///
+    /// or
+    ///
+    /// ```text
+    ///     <core::fmt::rt::Count>::Param(…)
+    /// ```
+    ///
+    /// or
+    ///
+    /// ```text
+    ///     <core::fmt::rt::Count>::Implied
+    /// ```
+    fn make_count(
+        &mut self,
+        count: &Option<FormatCount>,
+        argmap: &mut FxIndexSet<(usize, ArgumentType)>,
+    ) -> ExprId {
+        match count {
+            Some(FormatCount::Literal(n)) => {
+                match LangItem::FormatCount.ty_rel_path(self.db, self.krate, name![Is]) {
+                    Some(count_is) => {
+                        let count_is = self.alloc_expr_desugared(Expr::Path(count_is));
+                        let args = self.alloc_expr_desugared(Expr::Literal(Literal::Uint(
+                            *n as u128,
+                            Some(BuiltinUint::Usize),
+                        )));
+                        self.alloc_expr_desugared(Expr::Call {
+                            callee: count_is,
+                            args: Box::new([args]),
+                            is_assignee_expr: false,
+                        })
+                    }
+                    None => self.missing_expr(),
+                }
+            }
+            Some(FormatCount::Argument(arg)) => {
+                if let Ok(arg_index) = arg.index {
+                    let (i, _) = argmap.insert_full((arg_index, ArgumentType::Usize));
+
+                    match LangItem::FormatCount.ty_rel_path(self.db, self.krate, name![Param]) {
+                        Some(count_param) => {
+                            let count_param = self.alloc_expr_desugared(Expr::Path(count_param));
+                            let args = self.alloc_expr_desugared(Expr::Literal(Literal::Uint(
+                                i as u128,
+                                Some(BuiltinUint::Usize),
+                            )));
+                            self.alloc_expr_desugared(Expr::Call {
+                                callee: count_param,
+                                args: Box::new([args]),
+                                is_assignee_expr: false,
+                            })
+                        }
+                        None => self.missing_expr(),
+                    }
+                } else {
+                    self.missing_expr()
+                }
+            }
+            None => match LangItem::FormatCount.ty_rel_path(self.db, self.krate, name![Implied]) {
+                Some(count_param) => self.alloc_expr_desugared(Expr::Path(count_param)),
+                None => self.missing_expr(),
+            },
+        }
+    }
+
+    /// Generate a hir expression representing an argument to a format_args invocation.
+    ///
+    /// Generates:
+    ///
+    /// ```text
+    ///     <core::fmt::Argument>::new_…(arg)
+    /// ```
+    fn make_argument(&mut self, arg: ExprId, ty: ArgumentType) -> ExprId {
+        use ArgumentType::*;
+        use FormatTrait::*;
+        match LangItem::FormatArgument.ty_rel_path(
+            self.db,
+            self.krate,
+            match ty {
+                Format(Display) => name![new_display],
+                Format(Debug) => name![new_debug],
+                Format(LowerExp) => name![new_lower_exp],
+                Format(UpperExp) => name![new_upper_exp],
+                Format(Octal) => name![new_octal],
+                Format(Pointer) => name![new_pointer],
+                Format(Binary) => name![new_binary],
+                Format(LowerHex) => name![new_lower_hex],
+                Format(UpperHex) => name![new_upper_hex],
+                Usize => name![from_usize],
+            },
+        ) {
+            Some(new_fn) => {
+                let new_fn = self.alloc_expr_desugared(Expr::Path(new_fn));
+                self.alloc_expr_desugared(Expr::Call {
+                    callee: new_fn,
+                    args: Box::new([arg]),
+                    is_assignee_expr: false,
+                })
+            }
+            None => self.missing_expr(),
+        }
+    }
+    // endregion: format
 }
 
 fn pat_literal_to_hir(lit: &ast::LiteralPat) -> Option<(Literal, ast::Literal)> {
@@ -1606,3 +2033,9 @@ fn comma_follows_token(t: Option<syntax::SyntaxToken>) -> bool {
     (|| syntax::algo::skip_trivia_token(t?.next_token()?, syntax::Direction::Next))()
         .map_or(false, |it| it.kind() == syntax::T![,])
 }
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+enum ArgumentType {
+    Format(FormatTrait),
+    Usize,
+}

crates/hir-def/src/body/pretty.rs

@@ -2,7 +2,7 @@
 
 use std::fmt::{self, Write};
 
-use hir_expand::db::ExpandDatabase;
+use itertools::Itertools;
 use syntax::ast::HasName;
 
 use crate::{
@@ -51,8 +51,7 @@ pub(super) fn print_body_hir(db: &dyn DefDatabase, body: &Body, owner: DefWithBo
         }
     };
 
-    let mut p =
-        Printer { db: db.upcast(), body, buf: header, indent_level: 0, needs_indent: false };
+    let mut p = Printer { db, body, buf: header, indent_level: 0, needs_indent: false };
     if let DefWithBodyId::FunctionId(it) = owner {
         p.buf.push('(');
         body.params.iter().zip(&db.function_data(it).params).for_each(|(&param, ty)| {
@@ -76,8 +75,7 @@ pub(super) fn print_expr_hir(
     _owner: DefWithBodyId,
     expr: ExprId,
 ) -> String {
-    let mut p =
-        Printer { db: db.upcast(), body, buf: String::new(), indent_level: 0, needs_indent: false };
+    let mut p = Printer { db, body, buf: String::new(), indent_level: 0, needs_indent: false };
     p.print_expr(expr);
     p.buf
 }
@@ -98,7 +96,7 @@ macro_rules! wln {
 }
 
 struct Printer<'a> {
-    db: &'a dyn ExpandDatabase,
+    db: &'a dyn DefDatabase,
     body: &'a Body,
     buf: String,
     indent_level: usize,
@@ -142,9 +140,14 @@ impl Printer<'_> {
     }
 
     fn newline(&mut self) {
-        match self.buf.chars().rev().find(|ch| *ch != ' ') {
-            Some('\n') | None => {}
-            _ => writeln!(self).unwrap(),
+        match self.buf.chars().rev().find_position(|ch| *ch != ' ') {
+            Some((_, '\n')) | None => {}
+            Some((idx, _)) => {
+                if idx != 0 {
+                    self.buf.drain(self.buf.len() - idx..);
+                }
+                writeln!(self).unwrap()
+            }
         }
     }
 
@@ -154,6 +157,19 @@ impl Printer<'_> {
         match expr {
             Expr::Missing => w!(self, "<EFBFBD>"),
             Expr::Underscore => w!(self, "_"),
+            Expr::InlineAsm(_) => w!(self, "builtin#asm(_)"),
+            Expr::OffsetOf(offset_of) => {
+                w!(self, "builtin#offset_of(");
+                self.print_type_ref(&offset_of.container);
+                w!(
+                    self,
+                    ", {})",
+                    offset_of
+                        .fields
+                        .iter()
+                        .format_with(".", |field, f| f(&field.display(self.db.upcast())))
+                );
+            }
             Expr::Path(path) => self.print_path(path),
             Expr::If { condition, then_branch, else_branch } => {
                 w!(self, "if ");
@@ -173,7 +189,7 @@ impl Printer<'_> {
             }
             Expr::Loop { body, label } => {
                 if let Some(lbl) = label {
-                    w!(self, "{}: ", self.body[*lbl].name.display(self.db));
+                    w!(self, "{}: ", self.body[*lbl].name.display(self.db.upcast()));
                 }
                 w!(self, "loop ");
                 self.print_expr(*body);
@@ -193,7 +209,7 @@ impl Printer<'_> {
             }
             Expr::MethodCall { receiver, method_name, args, generic_args } => {
                 self.print_expr(*receiver);
-                w!(self, ".{}", method_name.display(self.db));
+                w!(self, ".{}", method_name.display(self.db.upcast()));
                 if let Some(args) = generic_args {
                     w!(self, "::<");
                     print_generic_args(self.db, args, self).unwrap();
@@ -231,13 +247,13 @@ impl Printer<'_> {
             Expr::Continue { label } => {
                 w!(self, "continue");
                 if let Some(lbl) = label {
-                    w!(self, " {}", self.body[*lbl].name.display(self.db));
+                    w!(self, " {}", self.body[*lbl].name.display(self.db.upcast()));
                 }
             }
             Expr::Break { expr, label } => {
                 w!(self, "break");
                 if let Some(lbl) = label {
-                    w!(self, " {}", self.body[*lbl].name.display(self.db));
+                    w!(self, " {}", self.body[*lbl].name.display(self.db.upcast()));
                 }
                 if let Some(expr) = expr {
                     self.whitespace();
@@ -276,7 +292,7 @@ impl Printer<'_> {
                 w!(self, "{{");
                 self.indented(|p| {
                     for field in &**fields {
-                        w!(p, "{}: ", field.name.display(self.db));
+                        w!(p, "{}: ", field.name.display(self.db.upcast()));
                         p.print_expr(field.expr);
                         wln!(p, ",");
                     }
@@ -293,7 +309,7 @@ impl Printer<'_> {
             }
             Expr::Field { expr, name } => {
                 self.print_expr(*expr);
-                w!(self, ".{}", name.display(self.db));
+                w!(self, ".{}", name.display(self.db.upcast()));
             }
             Expr::Await { expr } => {
                 self.print_expr(*expr);
@@ -431,7 +447,8 @@ impl Printer<'_> {
             }
             Expr::Literal(lit) => self.print_literal(lit),
             Expr::Block { id: _, statements, tail, label } => {
-                let label = label.map(|lbl| format!("{}: ", self.body[lbl].name.display(self.db)));
+                let label =
+                    label.map(|lbl| format!("{}: ", self.body[lbl].name.display(self.db.upcast())));
                 self.print_block(label.as_deref(), statements, tail);
             }
             Expr::Unsafe { id: _, statements, tail } => {
@@ -507,7 +524,7 @@ impl Printer<'_> {
                 w!(self, " {{");
                 self.indented(|p| {
                     for arg in args.iter() {
-                        w!(p, "{}: ", arg.name.display(self.db));
+                        w!(p, "{}: ", arg.name.display(self.db.upcast()));
                         p.print_pat(arg.pat);
                         wln!(p, ",");
                     }
@@ -666,6 +683,6 @@ impl Printer<'_> {
             BindingAnnotation::Ref => "ref ",
             BindingAnnotation::RefMut => "ref mut ",
         };
-        w!(self, "{}{}", mode, name.display(self.db));
+        w!(self, "{}{}", mode, name.display(self.db.upcast()));
     }
 }

crates/hir-def/src/body/tests.rs

@@ -1,13 +1,13 @@
 mod block;
 
 use base_db::{fixture::WithFixture, SourceDatabase};
-use expect_test::Expect;
+use expect_test::{expect, Expect};
 
 use crate::{test_db::TestDB, ModuleDefId};
 
 use super::*;
 
-fn lower(ra_fixture: &str) -> Arc<Body> {
+fn lower(ra_fixture: &str) -> (TestDB, Arc<Body>, DefWithBodyId) {
     let db = TestDB::with_files(ra_fixture);
 
     let krate = db.crate_graph().iter().next().unwrap();
@@ -21,8 +21,10 @@ fn lower(ra_fixture: &str) -> Arc<Body> {
             }
         }
     }
+    let fn_def = fn_def.unwrap().into();
 
-    db.body(fn_def.unwrap().into())
+    let body = db.body(fn_def);
+    (db, body, fn_def)
 }
 
 fn def_map_at(ra_fixture: &str) -> String {
@@ -138,3 +140,84 @@ mod m {
 "#,
     );
 }
+
+#[test]
+fn desugar_builtin_format_args() {
+    // Regression test for a path resolution bug introduced with inner item handling.
+    let (db, body, def) = lower(
+        r#"
+//- minicore: fmt
+fn main() {
+    let are = "are";
+    let count = 10;
+    builtin#format_args("hello {count:02} {} friends, we {are:?} {0}{last}", "fancy", last = "!");
+}
+"#,
+    );
+
+    expect![[r#"
+        fn main() {
+            let are = "are";
+            let count = 10;
+            builtin#lang(Arguments::new_v1_formatted)(
+                &[
+                    "\"hello ", " ", " friends, we ", " ", "", "\"",
+                ],
+                &[
+                    builtin#lang(Argument::new_display)(
+                        &count,
+                    ), builtin#lang(Argument::new_display)(
+                        &"fancy",
+                    ), builtin#lang(Argument::new_debug)(
+                        &are,
+                    ), builtin#lang(Argument::new_display)(
+                        &"!",
+                    ),
+                ],
+                &[
+                    builtin#lang(Placeholder::new)(
+                        0usize,
+                        ' ',
+                        builtin#lang(Alignment::Unknown),
+                        8u32,
+                        builtin#lang(Count::Implied),
+                        builtin#lang(Count::Is)(
+                            2usize,
+                        ),
+                    ), builtin#lang(Placeholder::new)(
+                        1usize,
+                        ' ',
+                        builtin#lang(Alignment::Unknown),
+                        0u32,
+                        builtin#lang(Count::Implied),
+                        builtin#lang(Count::Implied),
+                    ), builtin#lang(Placeholder::new)(
+                        2usize,
+                        ' ',
+                        builtin#lang(Alignment::Unknown),
+                        0u32,
+                        builtin#lang(Count::Implied),
+                        builtin#lang(Count::Implied),
+                    ), builtin#lang(Placeholder::new)(
+                        1usize,
+                        ' ',
+                        builtin#lang(Alignment::Unknown),
+                        0u32,
+                        builtin#lang(Count::Implied),
+                        builtin#lang(Count::Implied),
+                    ), builtin#lang(Placeholder::new)(
+                        3usize,
+                        ' ',
+                        builtin#lang(Alignment::Unknown),
+                        0u32,
+                        builtin#lang(Count::Implied),
+                        builtin#lang(Count::Implied),
+                    ),
+                ],
+                unsafe {
+                    builtin#lang(UnsafeArg::new)()
+                },
+            );
+        }"#]]
+    .assert_eq(&body.pretty_print(&db, def))
+}

crates/hir-def/src/data/adt.rs

@@ -447,6 +447,7 @@ impl VariantData {
         }
     }
 
+    // FIXME: Linear lookup
     pub fn field(&self, name: &Name) -> Option<LocalFieldId> {
         self.fields().iter().find_map(|(id, data)| if &data.name == name { Some(id) } else { None })
     }

crates/hir-def/src/find_path.rs

@@ -37,6 +37,20 @@ pub fn find_path_prefixed(
     find_path_inner(db, item, from, Some(prefix_kind), prefer_no_std)
 }
 
+#[derive(Copy, Clone, Debug)]
+enum Stability {
+    Unstable,
+    Stable,
+}
+use Stability::*;
+
+fn zip_stability(a: Stability, b: Stability) -> Stability {
+    match (a, b) {
+        (Stable, Stable) => Stable,
+        _ => Unstable,
+    }
+}
+
 const MAX_PATH_LEN: usize = 15;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -95,7 +109,8 @@ fn find_path_inner(
             MAX_PATH_LEN,
             prefixed,
             prefer_no_std || db.crate_supports_no_std(crate_root.krate),
-        );
+        )
+        .map(|(item, _)| item);
     }
 
     // - if the item is already in scope, return the name under which it is
@@ -143,6 +158,7 @@ fn find_path_inner(
         prefer_no_std || db.crate_supports_no_std(crate_root.krate),
         scope_name,
     )
+    .map(|(item, _)| item)
 }
 
 fn find_path_for_module(
@@ -155,7 +171,7 @@ fn find_path_for_module(
     max_len: usize,
     prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
-) -> Option<ModPath> {
+) -> Option<(ModPath, Stability)> {
     if max_len == 0 {
         return None;
     }
@@ -165,19 +181,19 @@ fn find_path_for_module(
     let scope_name = find_in_scope(db, def_map, from, ItemInNs::Types(module_id.into()));
     if prefixed.is_none() {
         if let Some(scope_name) = scope_name {
-            return Some(ModPath::from_segments(PathKind::Plain, Some(scope_name)));
+            return Some((ModPath::from_segments(PathKind::Plain, Some(scope_name)), Stable));
         }
     }
 
     // - if the item is the crate root, return `crate`
     if module_id == crate_root {
-        return Some(ModPath::from_segments(PathKind::Crate, None));
+        return Some((ModPath::from_segments(PathKind::Crate, None), Stable));
     }
 
     // - if relative paths are fine, check if we are searching for a parent
     if prefixed.filter(PrefixKind::is_absolute).is_none() {
         if let modpath @ Some(_) = find_self_super(def_map, module_id, from) {
-            return modpath;
+            return modpath.zip(Some(Stable));
         }
     }
 
@@ -201,14 +217,14 @@ fn find_path_for_module(
             } else {
                 PathKind::Plain
             };
-            return Some(ModPath::from_segments(kind, Some(name)));
+            return Some((ModPath::from_segments(kind, Some(name)), Stable));
         }
     }
 
     if let value @ Some(_) =
         find_in_prelude(db, &root_def_map, &def_map, ItemInNs::Types(module_id.into()), from)
     {
-        return value;
+        return value.zip(Some(Stable));
     }
     calculate_best_path(
         db,
@@ -301,11 +317,19 @@ fn calculate_best_path(
     mut prefixed: Option<PrefixKind>,
     prefer_no_std: bool,
     scope_name: Option<Name>,
-) -> Option<ModPath> {
+) -> Option<(ModPath, Stability)> {
     if max_len <= 1 {
         return None;
     }
     let mut best_path = None;
+    let update_best_path =
+        |best_path: &mut Option<_>, new_path: (ModPath, Stability)| match best_path {
+            Some((old_path, old_stability)) => {
+                *old_path = new_path.0;
+                *old_stability = zip_stability(*old_stability, new_path.1);
+            }
+            None => *best_path = Some(new_path),
+        };
     // Recursive case:
     // - otherwise, look for modules containing (reexporting) it and import it from one of those
     if item.krate(db) == Some(from.krate) {
@@ -328,14 +352,14 @@ fn calculate_best_path(
                 prefixed,
                 prefer_no_std,
             ) {
-                path.push_segment(name);
+                path.0.push_segment(name);
 
-                let new_path = match best_path {
+                let new_path = match best_path.take() {
                     Some(best_path) => select_best_path(best_path, path, prefer_no_std),
                     None => path,
                 };
-                best_path_len = new_path.len();
-                best_path = Some(new_path);
+                best_path_len = new_path.0.len();
+                update_best_path(&mut best_path, new_path);
             }
         }
     } else {
@@ -354,7 +378,7 @@ fn calculate_best_path(
 
                 // Determine best path for containing module and append last segment from `info`.
                 // FIXME: we should guide this to look up the path locally, or from the same crate again?
-                let mut path = find_path_for_module(
+                let (mut path, path_stability) = find_path_for_module(
                     db,
                     def_map,
                     visited_modules,
@@ -367,16 +391,19 @@ fn calculate_best_path(
                 )?;
                 cov_mark::hit!(partially_imported);
                 path.push_segment(info.name.clone());
-                Some(path)
+                Some((
+                    path,
+                    zip_stability(path_stability, if info.is_unstable { Unstable } else { Stable }),
+                ))
             })
         });
 
         for path in extern_paths {
-            let new_path = match best_path {
+            let new_path = match best_path.take() {
                 Some(best_path) => select_best_path(best_path, path, prefer_no_std),
                 None => path,
             };
-            best_path = Some(new_path);
+            update_best_path(&mut best_path, new_path);
         }
     }
     if let Some(module) = item.module(db) {
@@ -387,15 +414,24 @@ fn calculate_best_path(
     }
     match prefixed.map(PrefixKind::prefix) {
         Some(prefix) => best_path.or_else(|| {
-            scope_name.map(|scope_name| ModPath::from_segments(prefix, Some(scope_name)))
+            scope_name.map(|scope_name| (ModPath::from_segments(prefix, Some(scope_name)), Stable))
         }),
         None => best_path,
     }
 }
 
-fn select_best_path(old_path: ModPath, new_path: ModPath, prefer_no_std: bool) -> ModPath {
+fn select_best_path(
+    old_path: (ModPath, Stability),
+    new_path: (ModPath, Stability),
+    prefer_no_std: bool,
+) -> (ModPath, Stability) {
+    match (old_path.1, new_path.1) {
+        (Stable, Unstable) => return old_path,
+        (Unstable, Stable) => return new_path,
+        _ => {}
+    }
     const STD_CRATES: [Name; 3] = [known::std, known::core, known::alloc];
-    match (old_path.segments().first(), new_path.segments().first()) {
+    match (old_path.0.segments().first(), new_path.0.segments().first()) {
         (Some(old), Some(new)) if STD_CRATES.contains(old) && STD_CRATES.contains(new) => {
             let rank = match prefer_no_std {
                 false => |name: &Name| match name {
@@ -416,7 +452,7 @@ fn select_best_path(old_path: ModPath, new_path: ModPath, prefer_no_std: bool) -
             match nrank.cmp(&orank) {
                 Ordering::Less => old_path,
                 Ordering::Equal => {
-                    if new_path.len() < old_path.len() {
+                    if new_path.0.len() < old_path.0.len() {
                         new_path
                     } else {
                         old_path
@@ -426,7 +462,7 @@ fn select_best_path(old_path: ModPath, new_path: ModPath, prefer_no_std: bool) -
             }
         }
         _ => {
-            if new_path.len() < old_path.len() {
+            if new_path.0.len() < old_path.0.len() {
                 new_path
             } else {
                 old_path
@@ -1360,4 +1396,29 @@ pub mod ops {
             "std::ops::Deref",
         );
     }
+
+    #[test]
+    fn respect_unstable_modules() {
+        check_found_path(
+            r#"
+//- /main.rs crate:main deps:std,core
+#![no_std]
+extern crate std;
+$0
+//- /longer.rs crate:std deps:core
+pub mod error {
+    pub use core::error::Error;
+}
+//- /core.rs crate:core
+pub mod error {
+    #![unstable(feature = "error_in_core", issue = "103765")]
+    pub trait Error {}
+}
+"#,
+            "std::error::Error",
+            "std::error::Error",
+            "std::error::Error",
+            "std::error::Error",
+        );
+    }
 }

crates/hir-def/src/hir.rs

@@ -13,6 +13,7 @@
 //! See also a neighboring `body` module.
 
 pub mod type_ref;
+pub mod format_args;
 
 use std::fmt;
 
@@ -117,7 +118,6 @@ impl From<ast::LiteralKind> for Literal {
     fn from(ast_lit_kind: ast::LiteralKind) -> Self {
         use ast::LiteralKind;
         match ast_lit_kind {
-            // FIXME: these should have actual values filled in, but unsure on perf impact
             LiteralKind::IntNumber(lit) => {
                 if let builtin @ Some(_) = lit.suffix().and_then(BuiltinFloat::from_suffix) {
                     Literal::Float(
@@ -281,6 +281,19 @@ pub enum Expr {
     Array(Array),
     Literal(Literal),
     Underscore,
+    OffsetOf(OffsetOf),
+    InlineAsm(InlineAsm),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct OffsetOf {
+    pub container: Interned<TypeRef>,
+    pub fields: Box<[Name]>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct InlineAsm {
+    pub e: ExprId,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -341,7 +354,8 @@ impl Expr {
     pub fn walk_child_exprs(&self, mut f: impl FnMut(ExprId)) {
         match self {
             Expr::Missing => {}
-            Expr::Path(_) => {}
+            Expr::Path(_) | Expr::OffsetOf(_) => {}
+            Expr::InlineAsm(it) => f(it.e),
             Expr::If { condition, then_branch, else_branch } => {
                 f(*condition);
                 f(*then_branch);

crates/hir-def/src/hir/format_args.rs

@@ -0,0 +1,502 @@
+//! Parses `format_args` input.
+use std::mem;
+
+use hir_expand::name::Name;
+use rustc_parse_format as parse;
+use syntax::{
+    ast::{self, IsString},
+    AstToken, SmolStr, TextRange,
+};
+
+use crate::hir::ExprId;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FormatArgs {
+    pub template: Box<[FormatArgsPiece]>,
+    pub arguments: FormatArguments,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FormatArguments {
+    pub arguments: Box<[FormatArgument]>,
+    pub num_unnamed_args: usize,
+    pub num_explicit_args: usize,
+    pub names: Box<[(Name, usize)]>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum FormatArgsPiece {
+    Literal(Box<str>),
+    Placeholder(FormatPlaceholder),
+}
+
+#[derive(Copy, Debug, Clone, PartialEq, Eq)]
+pub struct FormatPlaceholder {
+    /// Index into [`FormatArgs::arguments`].
+    pub argument: FormatArgPosition,
+    /// The span inside the format string for the full `{…}` placeholder.
+    pub span: Option<TextRange>,
+    /// `{}`, `{:?}`, or `{:x}`, etc.
+    pub format_trait: FormatTrait,
+    /// `{}` or `{:.5}` or `{:-^20}`, etc.
+    pub format_options: FormatOptions,
+}
+
+#[derive(Copy, Debug, Clone, PartialEq, Eq)]
+pub struct FormatArgPosition {
+    /// Which argument this position refers to (Ok),
+    /// or would've referred to if it existed (Err).
+    pub index: Result<usize, usize>,
+    /// What kind of position this is. See [`FormatArgPositionKind`].
+    pub kind: FormatArgPositionKind,
+    /// The span of the name or number.
+    pub span: Option<TextRange>,
+}
+
+#[derive(Copy, Debug, Clone, PartialEq, Eq)]
+pub enum FormatArgPositionKind {
+    /// `{}` or `{:.*}`
+    Implicit,
+    /// `{1}` or `{:1$}` or `{:.1$}`
+    Number,
+    /// `{a}` or `{:a$}` or `{:.a$}`
+    Named,
+}
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+pub enum FormatTrait {
+    /// `{}`
+    Display,
+    /// `{:?}`
+    Debug,
+    /// `{:e}`
+    LowerExp,
+    /// `{:E}`
+    UpperExp,
+    /// `{:o}`
+    Octal,
+    /// `{:p}`
+    Pointer,
+    /// `{:b}`
+    Binary,
+    /// `{:x}`
+    LowerHex,
+    /// `{:X}`
+    UpperHex,
+}
+
+#[derive(Copy, Clone, Default, Debug, PartialEq, Eq)]
+pub struct FormatOptions {
+    /// The width. E.g. `{:5}` or `{:width$}`.
+    pub width: Option<FormatCount>,
+    /// The precision. E.g. `{:.5}` or `{:.precision$}`.
+    pub precision: Option<FormatCount>,
+    /// The alignment. E.g. `{:>}` or `{:<}` or `{:^}`.
+    pub alignment: Option<FormatAlignment>,
+    /// The fill character. E.g. the `.` in `{:.>10}`.
+    pub fill: Option<char>,
+    /// The `+` or `-` flag.
+    pub sign: Option<FormatSign>,
+    /// The `#` flag.
+    pub alternate: bool,
+    /// The `0` flag. E.g. the `0` in `{:02x}`.
+    pub zero_pad: bool,
+    /// The `x` or `X` flag (for `Debug` only). E.g. the `x` in `{:x?}`.
+    pub debug_hex: Option<FormatDebugHex>,
+}
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum FormatSign {
+    /// The `+` flag.
+    Plus,
+    /// The `-` flag.
+    Minus,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum FormatDebugHex {
+    /// The `x` flag in `{:x?}`.
+    Lower,
+    /// The `X` flag in `{:X?}`.
+    Upper,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum FormatAlignment {
+    /// `{:<}`
+    Left,
+    /// `{:>}`
+    Right,
+    /// `{:^}`
+    Center,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum FormatCount {
+    /// `{:5}` or `{:.5}`
+    Literal(usize),
+    /// `{:.*}`, `{:.5$}`, or `{:a$}`, etc.
+    Argument(FormatArgPosition),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FormatArgument {
+    pub kind: FormatArgumentKind,
+    pub expr: ExprId,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum FormatArgumentKind {
+    /// `format_args(…, arg)`
+    Normal,
+    /// `format_args(…, arg = 1)`
+    Named(Name),
+    /// `format_args("… {arg} …")`
+    Captured(Name),
+}
+
+// Only used in parse_args and report_invalid_references,
+// to indicate how a referred argument was used.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum PositionUsedAs {
+    Placeholder(Option<TextRange>),
+    Precision,
+    Width,
+}
+use PositionUsedAs::*;
+
+pub(crate) fn parse(
+    s: &ast::String,
+    fmt_snippet: Option<String>,
+    mut args: FormatArgumentsCollector,
+    is_direct_literal: bool,
+    mut synth: impl FnMut(Name) -> ExprId,
+) -> FormatArgs {
+    let text = s.text();
+    let str_style = match s.quote_offsets() {
+        Some(offsets) => {
+            let raw = u32::from(offsets.quotes.0.len()) - 1;
+            (raw != 0).then_some(raw as usize)
+        }
+        None => None,
+    };
+    let mut parser =
+        parse::Parser::new(text, str_style, fmt_snippet, false, parse::ParseMode::Format);
+
+    let mut pieces = Vec::new();
+    while let Some(piece) = parser.next() {
+        if !parser.errors.is_empty() {
+            break;
+        } else {
+            pieces.push(piece);
+        }
+    }
+    let is_source_literal = parser.is_source_literal;
+    if !parser.errors.is_empty() {
+        // FIXME: Diagnose
+        return FormatArgs { template: Default::default(), arguments: args.finish() };
+    }
+
+    let to_span = |inner_span: parse::InnerSpan| {
+        is_source_literal.then(|| {
+            TextRange::new(inner_span.start.try_into().unwrap(), inner_span.end.try_into().unwrap())
+        })
+    };
+
+    let mut used = vec![false; args.explicit_args().len()];
+    let mut invalid_refs = Vec::new();
+    let mut numeric_refences_to_named_arg = Vec::new();
+
+    enum ArgRef<'a> {
+        Index(usize),
+        Name(&'a str, Option<TextRange>),
+    }
+    let mut lookup_arg = |arg: ArgRef<'_>,
+                          span: Option<TextRange>,
+                          used_as: PositionUsedAs,
+                          kind: FormatArgPositionKind|
+     -> FormatArgPosition {
+        let index = match arg {
+            ArgRef::Index(index) => {
+                if let Some(arg) = args.by_index(index) {
+                    used[index] = true;
+                    if arg.kind.ident().is_some() {
+                        // This was a named argument, but it was used as a positional argument.
+                        numeric_refences_to_named_arg.push((index, span, used_as));
+                    }
+                    Ok(index)
+                } else {
+                    // Doesn't exist as an explicit argument.
+                    invalid_refs.push((index, span, used_as, kind));
+                    Err(index)
+                }
+            }
+            ArgRef::Name(name, _span) => {
+                let name = Name::new_text_dont_use(SmolStr::new(name));
+                if let Some((index, _)) = args.by_name(&name) {
+                    // Name found in `args`, so we resolve it to its index.
+                    if index < args.explicit_args().len() {
+                        // Mark it as used, if it was an explicit argument.
+                        used[index] = true;
+                    }
+                    Ok(index)
+                } else {
+                    // Name not found in `args`, so we add it as an implicitly captured argument.
+                    if !is_direct_literal {
+                        // For the moment capturing variables from format strings expanded from macros is
+                        // disabled (see RFC #2795)
+                        // FIXME: Diagnose
+                    }
+                    Ok(args.add(FormatArgument {
+                        kind: FormatArgumentKind::Captured(name.clone()),
+                        // FIXME: This is problematic, we might want to synthesize a dummy
+                        // expression proper and/or desugar these.
+                        expr: synth(name),
+                    }))
+                }
+            }
+        };
+        FormatArgPosition { index, kind, span }
+    };
+
+    let mut template = Vec::new();
+    let mut unfinished_literal = String::new();
+    let mut placeholder_index = 0;
+
+    for piece in pieces {
+        match piece {
+            parse::Piece::String(s) => {
+                unfinished_literal.push_str(s);
+            }
+            parse::Piece::NextArgument(arg) => {
+                let parse::Argument { position, position_span, format } = *arg;
+                if !unfinished_literal.is_empty() {
+                    template.push(FormatArgsPiece::Literal(
+                        mem::take(&mut unfinished_literal).into_boxed_str(),
+                    ));
+                }
+
+                let span = parser.arg_places.get(placeholder_index).and_then(|&s| to_span(s));
+                placeholder_index += 1;
+
+                let position_span = to_span(position_span);
+                let argument = match position {
+                    parse::ArgumentImplicitlyIs(i) => lookup_arg(
+                        ArgRef::Index(i),
+                        position_span,
+                        Placeholder(span),
+                        FormatArgPositionKind::Implicit,
+                    ),
+                    parse::ArgumentIs(i) => lookup_arg(
+                        ArgRef::Index(i),
+                        position_span,
+                        Placeholder(span),
+                        FormatArgPositionKind::Number,
+                    ),
+                    parse::ArgumentNamed(name) => lookup_arg(
+                        ArgRef::Name(name, position_span),
+                        position_span,
+                        Placeholder(span),
+                        FormatArgPositionKind::Named,
+                    ),
+                };
+
+                let alignment = match format.align {
+                    parse::AlignUnknown => None,
+                    parse::AlignLeft => Some(FormatAlignment::Left),
+                    parse::AlignRight => Some(FormatAlignment::Right),
+                    parse::AlignCenter => Some(FormatAlignment::Center),
+                };
+
+                let format_trait = match format.ty {
+                    "" => FormatTrait::Display,
+                    "?" => FormatTrait::Debug,
+                    "e" => FormatTrait::LowerExp,
+                    "E" => FormatTrait::UpperExp,
+                    "o" => FormatTrait::Octal,
+                    "p" => FormatTrait::Pointer,
+                    "b" => FormatTrait::Binary,
+                    "x" => FormatTrait::LowerHex,
+                    "X" => FormatTrait::UpperHex,
+                    _ => {
+                        // FIXME: Diagnose
+                        FormatTrait::Display
+                    }
+                };
+
+                let precision_span = format.precision_span.and_then(to_span);
+                let precision = match format.precision {
+                    parse::CountIs(n) => Some(FormatCount::Literal(n)),
+                    parse::CountIsName(name, name_span) => Some(FormatCount::Argument(lookup_arg(
+                        ArgRef::Name(name, to_span(name_span)),
+                        precision_span,
+                        Precision,
+                        FormatArgPositionKind::Named,
+                    ))),
+                    parse::CountIsParam(i) => Some(FormatCount::Argument(lookup_arg(
+                        ArgRef::Index(i),
+                        precision_span,
+                        Precision,
+                        FormatArgPositionKind::Number,
+                    ))),
+                    parse::CountIsStar(i) => Some(FormatCount::Argument(lookup_arg(
+                        ArgRef::Index(i),
+                        precision_span,
+                        Precision,
+                        FormatArgPositionKind::Implicit,
+                    ))),
+                    parse::CountImplied => None,
+                };
+
+                let width_span = format.width_span.and_then(to_span);
+                let width = match format.width {
+                    parse::CountIs(n) => Some(FormatCount::Literal(n)),
+                    parse::CountIsName(name, name_span) => Some(FormatCount::Argument(lookup_arg(
+                        ArgRef::Name(name, to_span(name_span)),
+                        width_span,
+                        Width,
+                        FormatArgPositionKind::Named,
+                    ))),
+                    parse::CountIsParam(i) => Some(FormatCount::Argument(lookup_arg(
+                        ArgRef::Index(i),
+                        width_span,
+                        Width,
+                        FormatArgPositionKind::Number,
+                    ))),
+                    parse::CountIsStar(_) => unreachable!(),
+                    parse::CountImplied => None,
+                };
+
+                template.push(FormatArgsPiece::Placeholder(FormatPlaceholder {
+                    argument,
+                    span,
+                    format_trait,
+                    format_options: FormatOptions {
+                        fill: format.fill,
+                        alignment,
+                        sign: format.sign.map(|s| match s {
+                            parse::Sign::Plus => FormatSign::Plus,
+                            parse::Sign::Minus => FormatSign::Minus,
+                        }),
+                        alternate: format.alternate,
+                        zero_pad: format.zero_pad,
+                        debug_hex: format.debug_hex.map(|s| match s {
+                            parse::DebugHex::Lower => FormatDebugHex::Lower,
+                            parse::DebugHex::Upper => FormatDebugHex::Upper,
+                        }),
+                        precision,
+                        width,
+                    },
+                }));
+            }
+        }
+    }
+
+    if !unfinished_literal.is_empty() {
+        template.push(FormatArgsPiece::Literal(unfinished_literal.into_boxed_str()));
+    }
+
+    if !invalid_refs.is_empty() {
+        // FIXME: Diagnose
+    }
+
+    let unused = used
+        .iter()
+        .enumerate()
+        .filter(|&(_, used)| !used)
+        .map(|(i, _)| {
+            let named = matches!(args.explicit_args()[i].kind, FormatArgumentKind::Named(_));
+            (args.explicit_args()[i].expr, named)
+        })
+        .collect::<Vec<_>>();
+
+    if !unused.is_empty() {
+        // FIXME: Diagnose
+    }
+
+    FormatArgs { template: template.into_boxed_slice(), arguments: args.finish() }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FormatArgumentsCollector {
+    arguments: Vec<FormatArgument>,
+    num_unnamed_args: usize,
+    num_explicit_args: usize,
+    names: Vec<(Name, usize)>,
+}
+
+impl FormatArgumentsCollector {
+    pub(crate) fn finish(self) -> FormatArguments {
+        FormatArguments {
+            arguments: self.arguments.into_boxed_slice(),
+            num_unnamed_args: self.num_unnamed_args,
+            num_explicit_args: self.num_explicit_args,
+            names: self.names.into_boxed_slice(),
+        }
+    }
+
+    pub fn new() -> Self {
+        Self { arguments: vec![], names: vec![], num_unnamed_args: 0, num_explicit_args: 0 }
+    }
+
+    pub fn add(&mut self, arg: FormatArgument) -> usize {
+        let index = self.arguments.len();
+        if let Some(name) = arg.kind.ident() {
+            self.names.push((name.clone(), index));
+        } else if self.names.is_empty() {
+            // Only count the unnamed args before the first named arg.
+            // (Any later ones are errors.)
+            self.num_unnamed_args += 1;
+        }
+        if !matches!(arg.kind, FormatArgumentKind::Captured(..)) {
+            // This is an explicit argument.
+            // Make sure that all arguments so far are explicit.
+            assert_eq!(
+                self.num_explicit_args,
+                self.arguments.len(),
+                "captured arguments must be added last"
+            );
+            self.num_explicit_args += 1;
+        }
+        self.arguments.push(arg);
+        index
+    }
+
+    pub fn by_name(&self, name: &Name) -> Option<(usize, &FormatArgument)> {
+        let &(_, i) = self.names.iter().find(|(n, _)| n == name)?;
+        Some((i, &self.arguments[i]))
+    }
+
+    pub fn by_index(&self, i: usize) -> Option<&FormatArgument> {
+        (i < self.num_explicit_args).then(|| &self.arguments[i])
+    }
+
+    pub fn unnamed_args(&self) -> &[FormatArgument] {
+        &self.arguments[..self.num_unnamed_args]
+    }
+
+    pub fn named_args(&self) -> &[FormatArgument] {
+        &self.arguments[self.num_unnamed_args..self.num_explicit_args]
+    }
+
+    pub fn explicit_args(&self) -> &[FormatArgument] {
+        &self.arguments[..self.num_explicit_args]
+    }
+
+    pub fn all_args(&self) -> &[FormatArgument] {
+        &self.arguments[..]
+    }
+
+    pub fn all_args_mut(&mut self) -> &mut Vec<FormatArgument> {
+        &mut self.arguments
+    }
+}
+
+impl FormatArgumentKind {
+    pub fn ident(&self) -> Option<&Name> {
+        match self {
+            Self::Normal => None,
+            Self::Named(id) => Some(id),
+            Self::Captured(id) => Some(id),
+        }
+    }
+}

crates/hir-def/src/import_map.rs

@@ -32,6 +32,8 @@ pub struct ImportInfo {
     pub is_trait_assoc_item: bool,
     /// Whether this item is annotated with `#[doc(hidden)]`.
     pub is_doc_hidden: bool,
+    /// Whether this item is annotated with `#[unstable(..)]`.
+    pub is_unstable: bool,
 }
 
 /// A map from publicly exported items to its name.
@@ -108,12 +110,15 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
 
         let visible_items = mod_data.scope.entries().filter_map(|(name, per_ns)| {
             let per_ns = per_ns.filter_visibility(|vis| vis == Visibility::Public);
-            if per_ns.is_none() { None } else { Some((name, per_ns)) }
+            if per_ns.is_none() {
+                None
+            } else {
+                Some((name, per_ns))
+            }
         });
 
         for (name, per_ns) in visible_items {
             for (item, import) in per_ns.iter_items() {
-                // FIXME: Not yet used, but will be once we handle doc(hidden) import sources
                 let attr_id = if let Some(import) = import {
                     match import {
                         ImportOrExternCrate::ExternCrate(id) => Some(id.into()),
@@ -125,28 +130,59 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
                         ItemInNs::Macros(id) => Some(id.into()),
                     }
                 };
-                let is_doc_hidden =
-                    attr_id.map_or(false, |attr_id| db.attrs(attr_id).has_doc_hidden());
+                let status @ (is_doc_hidden, is_unstable) =
+                    attr_id.map_or((false, false), |attr_id| {
+                        let attrs = db.attrs(attr_id);
+                        (attrs.has_doc_hidden(), attrs.is_unstable())
+                    });
 
                 let import_info = ImportInfo {
                     name: name.clone(),
                     container: module,
                     is_trait_assoc_item: false,
                     is_doc_hidden,
+                    is_unstable,
                 };
 
                 match depth_map.entry(item) {
-                    Entry::Vacant(entry) => _ = entry.insert((depth, is_doc_hidden)),
+                    Entry::Vacant(entry) => _ = entry.insert((depth, status)),
                     Entry::Occupied(mut entry) => {
-                        let &(occ_depth, occ_is_doc_hidden) = entry.get();
-                        // Prefer the one that is not doc(hidden),
-                        // Otherwise, if both have the same doc(hidden)-ness and the new path is shorter, prefer that one.
-                        let overwrite_entry = occ_is_doc_hidden && !is_doc_hidden
-                            || occ_is_doc_hidden == is_doc_hidden && depth < occ_depth;
-                        if !overwrite_entry {
+                        let &(occ_depth, (occ_is_doc_hidden, occ_is_unstable)) = entry.get();
+                        (depth, occ_depth);
+                        let overwrite = match (
+                            is_doc_hidden,
+                            occ_is_doc_hidden,
+                            is_unstable,
+                            occ_is_unstable,
+                        ) {
+                            // no change of hiddeness or unstableness
+                            (true, true, true, true)
+                            | (true, true, false, false)
+                            | (false, false, true, true)
+                            | (false, false, false, false) => depth < occ_depth,
+
+                            // either less hidden or less unstable, accept
+                            (true, true, false, true)
+                            | (false, true, true, true)
+                            | (false, true, false, true)
+                            | (false, true, false, false)
+                            | (false, false, false, true) => true,
+                            // more hidden or unstable, discard
+                            (true, true, true, false)
+                            | (true, false, true, true)
+                            | (true, false, true, false)
+                            | (true, false, false, false)
+                            | (false, false, true, false) => false,
+
+                            // exchanges doc(hidden) for unstable (and vice-versa),
+                            (true, false, false, true) | (false, true, true, false) => {
+                                depth < occ_depth
+                            }
+                        };
+                        if !overwrite {
                             continue;
                         }
-                        entry.insert((depth, is_doc_hidden));
+                        entry.insert((depth, status));
                     }
                 }
 
@@ -171,7 +207,7 @@ fn collect_import_map(db: &dyn DefDatabase, krate: CrateId) -> FxIndexMap<ItemIn
             }
         }
     }
-
+    map.shrink_to_fit();
     map
 }
 
@@ -200,11 +236,13 @@ fn collect_trait_assoc_items(
             ItemInNs::Values(module_def_id)
         };
 
+        let attrs = &db.attrs(item.into());
         let assoc_item_info = ImportInfo {
             container: trait_import_info.container,
             name: assoc_item_name.clone(),
             is_trait_assoc_item: true,
-            is_doc_hidden: db.attrs(item.into()).has_doc_hidden(),
+            is_doc_hidden: attrs.has_doc_hidden(),
+            is_unstable: attrs.is_unstable(),
         };
         map.insert(assoc_item, assoc_item_info);
     }

crates/hir-def/src/item_tree.rs

@@ -177,7 +177,7 @@ impl ItemTree {
     }
 
     pub fn pretty_print(&self, db: &dyn DefDatabase) -> String {
-        pretty::print_item_tree(db.upcast(), self)
+        pretty::print_item_tree(db, self)
     }
 
     fn data(&self) -> &ItemTreeData {

crates/hir-def/src/item_tree/pretty.rs

@@ -2,8 +2,6 @@
 
 use std::fmt::{self, Write};
 
-use hir_expand::db::ExpandDatabase;
-
 use crate::{
     generics::{TypeOrConstParamData, WherePredicate, WherePredicateTypeTarget},
     pretty::{print_path, print_type_bounds, print_type_ref},
@@ -12,7 +10,7 @@ use crate::{
 
 use super::*;
 
-pub(super) fn print_item_tree(db: &dyn ExpandDatabase, tree: &ItemTree) -> String {
+pub(super) fn print_item_tree(db: &dyn DefDatabase, tree: &ItemTree) -> String {
     let mut p = Printer { db, tree, buf: String::new(), indent_level: 0, needs_indent: true };
 
     if let Some(attrs) = tree.attrs.get(&AttrOwner::TopLevel) {
@@ -45,7 +43,7 @@ macro_rules! wln {
 }
 
 struct Printer<'a> {
-    db: &'a dyn ExpandDatabase,
+    db: &'a dyn DefDatabase,
     tree: &'a ItemTree,
     buf: String,
     indent_level: usize,
@@ -91,7 +89,7 @@ impl Printer<'_> {
                 self,
                 "#{}[{}{}]{}",
                 inner,
-                attr.path.display(self.db),
+                attr.path.display(self.db.upcast()),
                 attr.input.as_ref().map(|it| it.to_string()).unwrap_or_default(),
                 separated_by,
             );
@@ -106,7 +104,7 @@ impl Printer<'_> {
 
     fn print_visibility(&mut self, vis: RawVisibilityId) {
         match &self.tree[vis] {
-            RawVisibility::Module(path) => w!(self, "pub({}) ", path.display(self.db)),
+            RawVisibility::Module(path) => w!(self, "pub({}) ", path.display(self.db.upcast())),
             RawVisibility::Public => w!(self, "pub "),
         };
     }
@@ -121,7 +119,7 @@ impl Printer<'_> {
                         let Field { visibility, name, type_ref, ast_id: _ } = &this.tree[field];
                         this.print_attrs_of(field, "\n");
                         this.print_visibility(*visibility);
-                        w!(this, "{}: ", name.display(self.db));
+                        w!(this, "{}: ", name.display(self.db.upcast()));
                         this.print_type_ref(type_ref);
                         wln!(this, ",");
                     }
@@ -135,7 +133,7 @@ impl Printer<'_> {
                         let Field { visibility, name, type_ref, ast_id: _ } = &this.tree[field];
                         this.print_attrs_of(field, "\n");
                         this.print_visibility(*visibility);
-                        w!(this, "{}: ", name.display(self.db));
+                        w!(this, "{}: ", name.display(self.db.upcast()));
                         this.print_type_ref(type_ref);
                         wln!(this, ",");
                     }
@@ -168,20 +166,20 @@ impl Printer<'_> {
     fn print_use_tree(&mut self, use_tree: &UseTree) {
         match &use_tree.kind {
             UseTreeKind::Single { path, alias } => {
-                w!(self, "{}", path.display(self.db));
+                w!(self, "{}", path.display(self.db.upcast()));
                 if let Some(alias) = alias {
                     w!(self, " as {}", alias);
                 }
             }
             UseTreeKind::Glob { path } => {
                 if let Some(path) = path {
-                    w!(self, "{}::", path.display(self.db));
+                    w!(self, "{}::", path.display(self.db.upcast()));
                 }
                 w!(self, "*");
             }
             UseTreeKind::Prefixed { prefix, list } => {
                 if let Some(prefix) = prefix {
-                    w!(self, "{}::", prefix.display(self.db));
+                    w!(self, "{}::", prefix.display(self.db.upcast()));
                 }
                 w!(self, "{{");
                 for (i, tree) in list.iter().enumerate() {
@@ -209,7 +207,7 @@ impl Printer<'_> {
             ModItem::ExternCrate(it) => {
                 let ExternCrate { name, alias, visibility, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "extern crate {}", name.display(self.db));
+                w!(self, "extern crate {}", name.display(self.db.upcast()));
                 if let Some(alias) = alias {
                     w!(self, " as {}", alias);
                 }
@@ -256,7 +254,7 @@ impl Printer<'_> {
                 if let Some(abi) = abi {
                     w!(self, "extern \"{}\" ", abi);
                 }
-                w!(self, "fn {}", name.display(self.db));
+                w!(self, "fn {}", name.display(self.db.upcast()));
                 self.print_generic_params(explicit_generic_params);
                 w!(self, "(");
                 if !params.is_empty() {
@@ -290,7 +288,7 @@ impl Printer<'_> {
             ModItem::Struct(it) => {
                 let Struct { visibility, name, fields, generic_params, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "struct {}", name.display(self.db));
+                w!(self, "struct {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 self.print_fields_and_where_clause(fields, generic_params);
                 if matches!(fields, Fields::Record(_)) {
@@ -302,7 +300,7 @@ impl Printer<'_> {
             ModItem::Union(it) => {
                 let Union { name, visibility, fields, generic_params, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "union {}", name.display(self.db));
+                w!(self, "union {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 self.print_fields_and_where_clause(fields, generic_params);
                 if matches!(fields, Fields::Record(_)) {
@@ -314,14 +312,14 @@ impl Printer<'_> {
             ModItem::Enum(it) => {
                 let Enum { name, visibility, variants, generic_params, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "enum {}", name.display(self.db));
+                w!(self, "enum {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 self.print_where_clause_and_opening_brace(generic_params);
                 self.indented(|this| {
                     for variant in variants.clone() {
                         let Variant { name, fields, ast_id: _ } = &this.tree[variant];
                         this.print_attrs_of(variant, "\n");
-                        w!(this, "{}", name.display(self.db));
+                        w!(this, "{}", name.display(self.db.upcast()));
                         this.print_fields(fields);
                         wln!(this, ",");
                     }
@@ -333,7 +331,7 @@ impl Printer<'_> {
                 self.print_visibility(*visibility);
                 w!(self, "const ");
                 match name {
-                    Some(name) => w!(self, "{}", name.display(self.db)),
+                    Some(name) => w!(self, "{}", name.display(self.db.upcast())),
                     None => w!(self, "_"),
                 }
                 w!(self, ": ");
@@ -347,7 +345,7 @@ impl Printer<'_> {
                 if *mutable {
                     w!(self, "mut ");
                 }
-                w!(self, "{}: ", name.display(self.db));
+                w!(self, "{}: ", name.display(self.db.upcast()));
                 self.print_type_ref(type_ref);
                 w!(self, " = _;");
                 wln!(self);
@@ -369,7 +367,7 @@ impl Printer<'_> {
                 if *is_auto {
                     w!(self, "auto ");
                 }
-                w!(self, "trait {}", name.display(self.db));
+                w!(self, "trait {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 self.print_where_clause_and_opening_brace(generic_params);
                 self.indented(|this| {
@@ -382,7 +380,7 @@ impl Printer<'_> {
             ModItem::TraitAlias(it) => {
                 let TraitAlias { name, visibility, generic_params, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "trait {}", name.display(self.db));
+                w!(self, "trait {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 w!(self, " = ");
                 self.print_where_clause(generic_params);
@@ -415,7 +413,7 @@ impl Printer<'_> {
                 let TypeAlias { name, visibility, bounds, type_ref, generic_params, ast_id: _ } =
                     &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "type {}", name.display(self.db));
+                w!(self, "type {}", name.display(self.db.upcast()));
                 self.print_generic_params(generic_params);
                 if !bounds.is_empty() {
                     w!(self, ": ");
@@ -432,7 +430,7 @@ impl Printer<'_> {
             ModItem::Mod(it) => {
                 let Mod { name, visibility, kind, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                w!(self, "mod {}", name.display(self.db));
+                w!(self, "mod {}", name.display(self.db.upcast()));
                 match kind {
                     ModKind::Inline { items } => {
                         w!(self, " {{");
@@ -450,16 +448,16 @@ impl Printer<'_> {
             }
             ModItem::MacroCall(it) => {
                 let MacroCall { path, ast_id: _, expand_to: _ } = &self.tree[it];
-                wln!(self, "{}!(...);", path.display(self.db));
+                wln!(self, "{}!(...);", path.display(self.db.upcast()));
             }
             ModItem::MacroRules(it) => {
                 let MacroRules { name, ast_id: _ } = &self.tree[it];
-                wln!(self, "macro_rules! {} {{ ... }}", name.display(self.db));
+                wln!(self, "macro_rules! {} {{ ... }}", name.display(self.db.upcast()));
             }
             ModItem::MacroDef(it) => {
                 let MacroDef { name, visibility, ast_id: _ } = &self.tree[it];
                 self.print_visibility(*visibility);
-                wln!(self, "macro {} {{ ... }}", name.display(self.db));
+                wln!(self, "macro {} {{ ... }}", name.display(self.db.upcast()));
             }
         }
 
@@ -491,7 +489,7 @@ impl Printer<'_> {
             }
             first = false;
             self.print_attrs_of(idx, " ");
-            w!(self, "{}", lt.name.display(self.db));
+            w!(self, "{}", lt.name.display(self.db.upcast()));
         }
         for (idx, x) in params.type_or_consts.iter() {
             if !first {
@@ -501,11 +499,11 @@ impl Printer<'_> {
             self.print_attrs_of(idx, " ");
             match x {
                 TypeOrConstParamData::TypeParamData(ty) => match &ty.name {
-                    Some(name) => w!(self, "{}", name.display(self.db)),
+                    Some(name) => w!(self, "{}", name.display(self.db.upcast())),
                     None => w!(self, "_anon_{}", idx.into_raw()),
                 },
                 TypeOrConstParamData::ConstParamData(konst) => {
-                    w!(self, "const {}: ", konst.name.display(self.db));
+                    w!(self, "const {}: ", konst.name.display(self.db.upcast()));
                     self.print_type_ref(&konst.ty);
                 }
             }
@@ -540,8 +538,8 @@ impl Printer<'_> {
                         wln!(
                             this,
                             "{}: {},",
-                            target.name.display(self.db),
-                            bound.name.display(self.db)
+                            target.name.display(self.db.upcast()),
+                            bound.name.display(self.db.upcast())
                         );
                         continue;
                     }
@@ -551,7 +549,7 @@ impl Printer<'_> {
                             if i != 0 {
                                 w!(this, ", ");
                             }
-                            w!(this, "{}", lt.display(self.db));
+                            w!(this, "{}", lt.display(self.db.upcast()));
                         }
                         w!(this, "> ");
                         (target, bound)
@@ -562,7 +560,7 @@ impl Printer<'_> {
                     WherePredicateTypeTarget::TypeRef(ty) => this.print_type_ref(ty),
                     WherePredicateTypeTarget::TypeOrConstParam(id) => {
                         match &params.type_or_consts[*id].name() {
-                            Some(name) => w!(this, "{}", name.display(self.db)),
+                            Some(name) => w!(this, "{}", name.display(self.db.upcast())),
                             None => w!(this, "_anon_{}", id.into_raw()),
                         }
                     }

crates/hir-def/src/lang_item.rs

@@ -2,6 +2,7 @@
 //!
 //! This attribute to tell the compiler about semi built-in std library
 //! features, such as Fn family of traits.
+use hir_expand::name::Name;
 use rustc_hash::FxHashMap;
 use syntax::SmolStr;
 use triomphe::Arc;
@@ -238,7 +239,17 @@ impl LangItem {
 
     pub fn path(&self, db: &dyn DefDatabase, start_crate: CrateId) -> Option<Path> {
         let t = db.lang_item(start_crate, *self)?;
-        Some(Path::LangItem(t))
+        Some(Path::LangItem(t, None))
+    }
+
+    pub fn ty_rel_path(
+        &self,
+        db: &dyn DefDatabase,
+        start_crate: CrateId,
+        seg: Name,
+    ) -> Option<Path> {
+        let t = db.lang_item(start_crate, *self)?;
+        Some(Path::LangItem(t, Some(seg)))
     }
 }
 

crates/hir-def/src/lower.rs

@@ -1,10 +1,11 @@
 //! Context for lowering paths.
+use std::cell::OnceCell;
+
 use hir_expand::{
     ast_id_map::{AstIdMap, AstIdNode},
     hygiene::Hygiene,
     AstId, HirFileId, InFile,
 };
-use once_cell::unsync::OnceCell;
 use syntax::ast;
 use triomphe::Arc;
 

crates/hir-def/src/macro_expansion_tests/builtin_fn_macro.rs

@@ -22,6 +22,45 @@ fn main() { 0 as u32; }
     );
 }
 
+#[test]
+fn test_asm_expand() {
+    check(
+        r#"
+#[rustc_builtin_macro]
+macro_rules! asm {() => {}}
+
+fn main() {
+    let i: u64 = 3;
+    let o: u64;
+    unsafe {
+        asm!(
+            "mov {0}, {1}",
+            "add {0}, 5",
+            out(reg) o,
+            in(reg) i,
+        );
+    }
+}
+"#,
+        expect![[r##"
+#[rustc_builtin_macro]
+macro_rules! asm {() => {}}
+
+fn main() {
+    let i: u64 = 3;
+    let o: u64;
+    unsafe {
+        builtin #asm ( {
+            $crate::format_args!("mov {0}, {1}");
+            $crate::format_args!("add {0}, 5");
+        }
+        );
+    }
+}
+"##]],
+    );
+}
+
 #[test]
 fn test_line_expand() {
     check(
@@ -201,7 +240,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    ::core::fmt::Arguments::new_v1(&["", " ", ], &[::core::fmt::ArgumentV1::new(&(arg1(a, b, c)), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(arg2), ::core::fmt::Debug::fmt), ]);
+    builtin #format_args ("{} {:?}", arg1(a, b, c), arg2);
 }
 "##]],
     );
@@ -219,10 +258,10 @@ macro_rules! format_args {
 
 fn main() {
     format_args!(x = 2);
-    format_args!(x =);
-    format_args!(x =, x = 2);
-    format_args!("{}", x =);
-    format_args!(=, "{}", x =);
+    format_args!/*+errors*/(x =);
+    format_args!/*+errors*/(x =, x = 2);
+    format_args!/*+errors*/("{}", x =);
+    format_args!/*+errors*/(=, "{}", x =);
     format_args!(x = 2, "{}", 5);
 }
 "#,
@@ -234,12 +273,19 @@ macro_rules! format_args {
 }
 
 fn main() {
-    /* error: no rule matches input tokens */;
-    /* error: expected expression */;
-    /* error: expected expression, expected COMMA */;
-    /* error: expected expression */::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::ArgumentV1::new(&(), ::core::fmt::Display::fmt), ]);
-    /* error: expected expression, expected R_PAREN */;
-    ::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::ArgumentV1::new(&(5), ::core::fmt::Display::fmt), ]);
+    builtin #format_args (x = 2);
+    /* parse error: expected expression */
+builtin #format_args (x = );
+    /* parse error: expected expression */
+/* parse error: expected R_PAREN */
+/* parse error: expected expression, item or let statement */
+builtin #format_args (x = , x = 2);
+    /* parse error: expected expression */
+builtin #format_args ("{}", x = );
+    /* parse error: expected expression */
+/* parse error: expected expression */
+builtin #format_args ( = , "{}", x = );
+    builtin #format_args (x = 2, "{}", 5);
 }
 "##]],
     );
@@ -267,7 +313,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    ::core::fmt::Arguments::new_v1(&["", " ", ], &[::core::fmt::ArgumentV1::new(&(a::<A, B>()), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(b), ::core::fmt::Debug::fmt), ]);
+    builtin #format_args ("{} {:?}", a::<A, B>(), b);
 }
 "##]],
     );
@@ -300,7 +346,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    ::core::fmt::Arguments::new_v1(&[r#""#, r#",mismatch,""#, r#"",""#, r#"""#, ], &[::core::fmt::ArgumentV1::new(&(location_csv_pat(db, &analysis, vfs, &sm, pat_id)), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(mismatch.expected.display(db)), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(mismatch.actual.display(db)), ::core::fmt::Display::fmt), ]);
+    builtin #format_args (r#"{},mismatch,"{}","{}""#, location_csv_pat(db, &analysis, vfs, &sm, pat_id), mismatch.expected.display(db), mismatch.actual.display(db));
 }
 "##]],
     );
@@ -334,7 +380,7 @@ macro_rules! format_args {
 }
 
 fn main() {
-    ::core::fmt::Arguments::new_v1(&["xxx", "y", "zzz", ], &[::core::fmt::ArgumentV1::new(&(2), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(b), ::core::fmt::Debug::fmt), ]);
+    builtin #format_args (concat!("xxx{}y", "{:?}zzz"), 2, b);
 }
 "##]],
     );
@@ -364,8 +410,8 @@ macro_rules! format_args {
 
 fn main() {
     let _ =
-        /* error: expected field name or number *//* parse error: expected field name or number */
-::core::fmt::Arguments::new_v1(&["", " ", ], &[::core::fmt::ArgumentV1::new(&(a.), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(), ::core::fmt::Debug::fmt), ]);
+        /* parse error: expected field name or number */
+builtin #format_args ("{} {:?}", a.);
 }
 "##]],
     );

crates/hir-def/src/macro_expansion_tests/mbe.rs

@@ -117,7 +117,7 @@ fn main(foo: ()) {
 macro_rules! format_args {}
 
 fn main(foo: ()) {
-    /* error: unresolved macro identity */::core::fmt::Arguments::new_v1(&["", " ", " ", ], &[::core::fmt::ArgumentV1::new(&(::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::ArgumentV1::new(&(0), ::core::fmt::Display::fmt), ])), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(foo), ::core::fmt::Display::fmt), ::core::fmt::ArgumentV1::new(&(identity!(10)), ::core::fmt::Display::fmt), ])
+    builtin #format_args ("{} {} {}", format_args!("{}", 0), foo, identity!(10), "bar")
 }
 "##]],
     );
@@ -150,8 +150,8 @@ macro_rules! identity {
 }
 
 fn main(foo: ()) {
-    // format_args/*+tokenids*/!("{} {} {}"#1,#3 format_args!("{}", 0#10),#12 foo#13,#14 identity!(10#18),#21 "bar"#22)
-::core#4294967295::fmt#4294967295::Arguments#4294967295::new_v1#4294967295(&#4294967295[#4294967295""#4294967295,#4294967295 " "#4294967295,#4294967295 " "#4294967295,#4294967295 ]#4294967295,#4294967295 &#4294967295[::core#4294967295::fmt#4294967295::ArgumentV1#4294967295::new#4294967295(&#4294967295(::core#4294967295::fmt#4294967295::Arguments#4294967295::new_v1#4294967295(&#4294967295[#4294967295""#4294967295,#4294967295 ]#4294967295,#4294967295 &#4294967295[::core#4294967295::fmt#4294967295::ArgumentV1#4294967295::new#4294967295(&#4294967295(#42949672950#10)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::Display#4294967295::fmt#4294967295)#4294967295,#4294967295 ]#4294967295)#4294967295)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::Display#4294967295::fmt#4294967295)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::ArgumentV1#4294967295::new#4294967295(&#4294967295(#4294967295foo#13)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::Display#4294967295::fmt#4294967295)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::ArgumentV1#4294967295::new#4294967295(&#4294967295(#429496729510#18)#4294967295,#4294967295 ::core#4294967295::fmt#4294967295::Display#4294967295::fmt#4294967295)#4294967295,#4294967295 ]#4294967295)#4294967295
+    // format_args/*+tokenids*/!("{} {} {}"#1,#2 format_args#3!#4("{}"#6,#7 0#8),#9 foo#10,#11 identity#12!#13(10#15),#16 "bar"#17)
+builtin#4294967295 ##4294967295format_args#4294967295 (#0"{} {} {}"#1,#2 format_args#3!#4(#5"{}"#6,#7 0#8)#5,#9 foo#10,#11 identity#12!#13(#1410#15)#14,#16 "bar"#17)#0
 }
 
 "##]],

crates/hir-def/src/macro_expansion_tests/mbe/regression.rs

@@ -929,8 +929,8 @@ fn main() {
 macro_rules! format_args {}
 
 fn main() {
-    /* error: expected field name or number *//* parse error: expected field name or number */
-::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::ArgumentV1::new(&(line.1.), ::core::fmt::Display::fmt), ]);
+    /* parse error: expected field name or number */
+builtin #format_args ("{}", line.1.);
 }
 
 "##]],
@@ -956,19 +956,15 @@ fn main() {
 macro_rules! format_args {}
 
 fn main() {
-    /* error: expected COMMA, expected R_BRACK, expected COMMA, expected COMMA, expected expression, expected R_PAREN *//* parse error: expected COMMA */
+    /* parse error: expected COMMA */
 /* parse error: expected R_BRACK */
 /* parse error: expected COMMA */
 /* parse error: expected COMMA */
 /* parse error: expected expression */
 /* parse error: expected R_PAREN */
-/* parse error: expected R_PAREN */
 /* parse error: expected expression, item or let statement */
 /* parse error: expected expression, item or let statement */
-/* parse error: expected expression, item or let statement */
-/* parse error: expected expression, item or let statement */
-/* parse error: expected expression, item or let statement */
-::core::fmt::Arguments::new_v1(&["", ], &[::core::fmt::ArgumentV1::new(&(&[0 2]), ::core::fmt::Display::fmt), ]);
+builtin #format_args ("{}", &[0 2]);
 }
 
 "##]],

crates/hir-def/src/nameres.rs

@@ -93,7 +93,7 @@ use crate::{
 #[derive(Debug, PartialEq, Eq)]
 pub struct DefMap {
     _c: Count<Self>,
-    /// When this is a block def map, this will hold the block id of the the block and module that
+    /// When this is a block def map, this will hold the block id of the block and module that
     /// contains this block.
     block: Option<BlockInfo>,
     /// The modules and their data declared in this crate.

crates/hir-def/src/nameres/collector.rs

@@ -1828,7 +1828,11 @@ impl ModCollector<'_, '_> {
             let Some(paths) = attr.parse_path_comma_token_tree(db.upcast(), &hygiene) else {
                 // `#[macro_use]` (without any paths) found, forget collected names and just import
                 // all visible macros.
-                self.def_collector.import_macros_from_extern_crate(target_crate, None, Some(extern_crate_id));
+                self.def_collector.import_macros_from_extern_crate(
+                    target_crate,
+                    None,
+                    Some(extern_crate_id),
+                );
                 return;
             };
             for path in paths {

crates/hir-def/src/path.rs

@@ -47,7 +47,7 @@ pub enum Path {
     },
     /// A link to a lang item. It is used in desugaring of things like `it?`. We can show these
     /// links via a normal path since they might be private and not accessible in the usage place.
-    LangItem(LangItemTarget),
+    LangItem(LangItemTarget, Option<Name>),
 }
 
 /// Generic arguments to a path segment (e.g. the `i32` in `Option<i32>`). This
@@ -122,33 +122,40 @@ impl Path {
     pub fn kind(&self) -> &PathKind {
         match self {
             Path::Normal { mod_path, .. } => &mod_path.kind,
-            Path::LangItem(_) => &PathKind::Abs,
+            Path::LangItem(..) => &PathKind::Abs,
         }
     }
 
     pub fn type_anchor(&self) -> Option<&TypeRef> {
         match self {
             Path::Normal { type_anchor, .. } => type_anchor.as_deref(),
-            Path::LangItem(_) => None,
+            Path::LangItem(..) => None,
         }
     }
 
     pub fn segments(&self) -> PathSegments<'_> {
-        let Path::Normal { mod_path, generic_args, .. } = self else {
-            return PathSegments { segments: &[], generic_args: None };
-        };
-        let s =
-            PathSegments { segments: mod_path.segments(), generic_args: generic_args.as_deref() };
-        if let Some(generic_args) = s.generic_args {
-            assert_eq!(s.segments.len(), generic_args.len());
+        match self {
+            Path::Normal { mod_path, generic_args, .. } => {
+                let s = PathSegments {
+                    segments: mod_path.segments(),
+                    generic_args: generic_args.as_deref(),
+                };
+                if let Some(generic_args) = s.generic_args {
+                    assert_eq!(s.segments.len(), generic_args.len());
+                }
+                s
+            }
+            Path::LangItem(_, seg) => PathSegments {
+                segments: seg.as_ref().map_or(&[], |seg| std::slice::from_ref(seg)),
+                generic_args: None,
+            },
         }
-        s
     }
 
     pub fn mod_path(&self) -> Option<&ModPath> {
         match self {
             Path::Normal { mod_path, .. } => Some(&mod_path),
-            Path::LangItem(_) => None,
+            Path::LangItem(..) => None,
         }
     }
 

crates/hir-def/src/pretty.rs

@@ -2,18 +2,54 @@
 
 use std::fmt::{self, Write};
 
-use hir_expand::{db::ExpandDatabase, mod_path::PathKind};
+use hir_expand::mod_path::PathKind;
 use intern::Interned;
 use itertools::Itertools;
 
 use crate::{
+    db::DefDatabase,
+    lang_item::LangItemTarget,
     path::{GenericArg, GenericArgs, Path},
     type_ref::{Mutability, TraitBoundModifier, TypeBound, TypeRef},
 };
 
-pub(crate) fn print_path(db: &dyn ExpandDatabase, path: &Path, buf: &mut dyn Write) -> fmt::Result {
-    if let Path::LangItem(it) = path {
-        return write!(buf, "$lang_item::{it:?}");
+pub(crate) fn print_path(db: &dyn DefDatabase, path: &Path, buf: &mut dyn Write) -> fmt::Result {
+    if let Path::LangItem(it, s) = path {
+        write!(buf, "builtin#lang(")?;
+        match *it {
+            LangItemTarget::ImplDef(it) => write!(buf, "{it:?}")?,
+            LangItemTarget::EnumId(it) => {
+                write!(buf, "{}", db.enum_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::Function(it) => {
+                write!(buf, "{}", db.function_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::Static(it) => {
+                write!(buf, "{}", db.static_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::Struct(it) => {
+                write!(buf, "{}", db.struct_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::Union(it) => {
+                write!(buf, "{}", db.union_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::TypeAlias(it) => {
+                write!(buf, "{}", db.type_alias_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::Trait(it) => {
+                write!(buf, "{}", db.trait_data(it).name.display(db.upcast()))?
+            }
+            LangItemTarget::EnumVariant(it) => write!(
+                buf,
+                "{}",
+                db.enum_data(it.parent).variants[it.local_id].name.display(db.upcast())
+            )?,
+        }
+
+        if let Some(s) = s {
+            write!(buf, "::{}", s.display(db.upcast()))?;
+        }
+        return write!(buf, ")");
     }
     match path.type_anchor() {
         Some(anchor) => {
@@ -44,7 +80,7 @@ pub(crate) fn print_path(db: &dyn ExpandDatabase, path: &Path, buf: &mut dyn Wri
             write!(buf, "::")?;
         }
 
-        write!(buf, "{}", segment.name.display(db))?;
+        write!(buf, "{}", segment.name.display(db.upcast()))?;
         if let Some(generics) = segment.args_and_bindings {
             write!(buf, "::<")?;
             print_generic_args(db, generics, buf)?;
@@ -57,7 +93,7 @@ pub(crate) fn print_path(db: &dyn ExpandDatabase, path: &Path, buf: &mut dyn Wri
 }
 
 pub(crate) fn print_generic_args(
-    db: &dyn ExpandDatabase,
+    db: &dyn DefDatabase,
     generics: &GenericArgs,
     buf: &mut dyn Write,
 ) -> fmt::Result {
@@ -83,7 +119,7 @@ pub(crate) fn print_generic_args(
             write!(buf, ", ")?;
         }
         first = false;
-        write!(buf, "{}", binding.name.display(db))?;
+        write!(buf, "{}", binding.name.display(db.upcast()))?;
         if !binding.bounds.is_empty() {
             write!(buf, ": ")?;
             print_type_bounds(db, &binding.bounds, buf)?;
@@ -97,19 +133,19 @@ pub(crate) fn print_generic_args(
 }
 
 pub(crate) fn print_generic_arg(
-    db: &dyn ExpandDatabase,
+    db: &dyn DefDatabase,
     arg: &GenericArg,
     buf: &mut dyn Write,
 ) -> fmt::Result {
     match arg {
         GenericArg::Type(ty) => print_type_ref(db, ty, buf),
-        GenericArg::Const(c) => write!(buf, "{}", c.display(db)),
-        GenericArg::Lifetime(lt) => write!(buf, "{}", lt.name.display(db)),
+        GenericArg::Const(c) => write!(buf, "{}", c.display(db.upcast())),
+        GenericArg::Lifetime(lt) => write!(buf, "{}", lt.name.display(db.upcast())),
     }
 }
 
 pub(crate) fn print_type_ref(
-    db: &dyn ExpandDatabase,
+    db: &dyn DefDatabase,
     type_ref: &TypeRef,
     buf: &mut dyn Write,
 ) -> fmt::Result {
@@ -143,7 +179,7 @@ pub(crate) fn print_type_ref(
             };
             write!(buf, "&")?;
             if let Some(lt) = lt {
-                write!(buf, "{} ", lt.name.display(db))?;
+                write!(buf, "{} ", lt.name.display(db.upcast()))?;
             }
             write!(buf, "{mtbl}")?;
             print_type_ref(db, pointee, buf)?;
@@ -151,7 +187,7 @@ pub(crate) fn print_type_ref(
         TypeRef::Array(elem, len) => {
             write!(buf, "[")?;
             print_type_ref(db, elem, buf)?;
-            write!(buf, "; {}]", len.display(db))?;
+            write!(buf, "; {}]", len.display(db.upcast()))?;
         }
         TypeRef::Slice(elem) => {
             write!(buf, "[")?;
@@ -198,7 +234,7 @@ pub(crate) fn print_type_ref(
 }
 
 pub(crate) fn print_type_bounds(
-    db: &dyn ExpandDatabase,
+    db: &dyn DefDatabase,
     bounds: &[Interned<TypeBound>],
     buf: &mut dyn Write,
 ) -> fmt::Result {
@@ -216,10 +252,14 @@ pub(crate) fn print_type_bounds(
                 print_path(db, path, buf)?;
             }
             TypeBound::ForLifetime(lifetimes, path) => {
-                write!(buf, "for<{}> ", lifetimes.iter().map(|it| it.display(db)).format(", "))?;
+                write!(
+                    buf,
+                    "for<{}> ",
+                    lifetimes.iter().map(|it| it.display(db.upcast())).format(", ")
+                )?;
                 print_path(db, path, buf)?;
             }
-            TypeBound::Lifetime(lt) => write!(buf, "{}", lt.name.display(db))?,
+            TypeBound::Lifetime(lt) => write!(buf, "{}", lt.name.display(db.upcast()))?,
             TypeBound::Error => write!(buf, "{{unknown}}")?,
         }
     }

crates/hir-def/src/resolver.rs

@@ -156,22 +156,19 @@ impl Resolver {
     ) -> Option<(TypeNs, Option<usize>, Option<ImportOrExternCrate>)> {
         let path = match path {
             Path::Normal { mod_path, .. } => mod_path,
-            Path::LangItem(l) => {
-                return Some((
-                    match *l {
-                        LangItemTarget::Union(it) => TypeNs::AdtId(it.into()),
-                        LangItemTarget::TypeAlias(it) => TypeNs::TypeAliasId(it),
-                        LangItemTarget::Struct(it) => TypeNs::AdtId(it.into()),
-                        LangItemTarget::EnumVariant(it) => TypeNs::EnumVariantId(it),
-                        LangItemTarget::EnumId(it) => TypeNs::AdtId(it.into()),
-                        LangItemTarget::Trait(it) => TypeNs::TraitId(it),
-                        LangItemTarget::Function(_)
-                        | LangItemTarget::ImplDef(_)
-                        | LangItemTarget::Static(_) => return None,
-                    },
-                    None,
-                    None,
-                ))
+            Path::LangItem(l, seg) => {
+                let type_ns = match *l {
+                    LangItemTarget::Union(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::TypeAlias(it) => TypeNs::TypeAliasId(it),
+                    LangItemTarget::Struct(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::EnumVariant(it) => TypeNs::EnumVariantId(it),
+                    LangItemTarget::EnumId(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::Trait(it) => TypeNs::TraitId(it),
+                    LangItemTarget::Function(_)
+                    | LangItemTarget::ImplDef(_)
+                    | LangItemTarget::Static(_) => return None,
+                };
+                return Some((type_ns, seg.as_ref().map(|_| 1), None));
             }
         };
         let first_name = path.segments().first()?;
@@ -256,7 +253,7 @@ impl Resolver {
     ) -> Option<ResolveValueResult> {
         let path = match path {
             Path::Normal { mod_path, .. } => mod_path,
-            Path::LangItem(l) => {
+            Path::LangItem(l, None) => {
                 return Some(ResolveValueResult::ValueNs(
                     match *l {
                         LangItemTarget::Function(it) => ValueNs::FunctionId(it),
@@ -272,6 +269,20 @@ impl Resolver {
                     None,
                 ))
             }
+            Path::LangItem(l, Some(_)) => {
+                let type_ns = match *l {
+                    LangItemTarget::Union(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::TypeAlias(it) => TypeNs::TypeAliasId(it),
+                    LangItemTarget::Struct(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::EnumVariant(it) => TypeNs::EnumVariantId(it),
+                    LangItemTarget::EnumId(it) => TypeNs::AdtId(it.into()),
+                    LangItemTarget::Trait(it) => TypeNs::TraitId(it),
+                    LangItemTarget::Function(_)
+                    | LangItemTarget::ImplDef(_)
+                    | LangItemTarget::Static(_) => return None,
+                };
+                return Some(ResolveValueResult::Partial(type_ns, 1, None));
+            }
         };
         let n_segments = path.segments().len();
         let tmp = name![self];