Merge #2962

2962: Differentiate underscore alias from named aliases r=matklad a=zombiefungus

pre for Fixing Issue 2736 
edited to avoid autoclosing the issue

Co-authored-by: zombiefungus <divmermarlav@gmail.com>

crates/ra_hir_def/src/nameres/collector.rs

@@ -22,7 +22,7 @@ use crate::{
         diagnostics::DefDiagnostic, mod_resolution::ModDir, path_resolution::ReachedFixedPoint,
         raw, BuiltinShadowMode, CrateDefMap, ModuleData, ModuleOrigin, ResolveMode,
     },
-    path::{ModPath, PathKind},
+    path::{ImportAlias, ModPath, PathKind},
     per_ns::PerNs,
     visibility::Visibility,
     AdtId, AstId, ConstLoc, ContainerId, EnumLoc, EnumVariantId, FunctionLoc, ImplLoc, Intern,
@@ -438,7 +438,11 @@ where
         } else {
             match import.path.segments.last() {
                 Some(last_segment) => {
-                    let name = import.alias.clone().unwrap_or_else(|| last_segment.clone());
+                    let name = match &import.alias {
+                        Some(ImportAlias::Alias(name)) => name.clone(),
+                        Some(ImportAlias::Underscore) => last_segment.clone(), // FIXME rust-analyzer#2736
+                        None => last_segment.clone(),
+                    };
                     log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def);
 
                     // extern crates in the crate root are special-cased to insert entries into the extern prelude: rust-lang/rust#54658

crates/ra_hir_def/src/nameres/raw.rs

@@ -22,8 +22,11 @@ use ra_syntax::{
 use test_utils::tested_by;
 
 use crate::{
-    attr::Attrs, db::DefDatabase, path::ModPath, visibility::RawVisibility, FileAstId, HirFileId,
+    attr::Attrs,
-    InFile,
+    db::DefDatabase,
+    path::{ImportAlias, ModPath},
+    visibility::RawVisibility,
+    FileAstId, HirFileId, InFile,
 };
 
 /// `RawItems` is a set of top-level items in a file (except for impls).
@@ -145,7 +148,7 @@ impl_arena_id!(Import);
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ImportData {
     pub(super) path: ModPath,
-    pub(super) alias: Option<Name>,
+    pub(super) alias: Option<ImportAlias>,
     pub(super) is_glob: bool,
     pub(super) is_prelude: bool,
     pub(super) is_extern_crate: bool,
@@ -353,7 +356,11 @@ impl RawItemsCollector {
             let path = ModPath::from_name_ref(&name_ref);
             let visibility =
                 RawVisibility::from_ast_with_hygiene(extern_crate.visibility(), &self.hygiene);
-            let alias = extern_crate.alias().and_then(|a| a.name()).map(|it| it.as_name());
+            let alias = extern_crate.alias().map(|a| {
+                a.name()
+                    .map(|it| it.as_name())
+                    .map_or(ImportAlias::Underscore, |a| ImportAlias::Alias(a))
+            });
             let attrs = self.parse_attrs(&extern_crate);
             // FIXME: cfg_attr
             let is_macro_use = extern_crate.has_atom_attr("macro_use");

crates/ra_hir_def/src/path.rs

@@ -34,6 +34,14 @@ pub enum PathKind {
     DollarCrate(CrateId),
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ImportAlias {
+    /// Unnamed alias, as in `use Foo as _;`
+    Underscore,
+    /// Named alias
+    Alias(Name),
+}
+
 impl ModPath {
     pub fn from_src(path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
         lower::lower_path(path, hygiene).map(|it| it.mod_path)
@@ -57,7 +65,7 @@ impl ModPath {
     pub(crate) fn expand_use_item(
         item_src: InFile<ast::UseItem>,
         hygiene: &Hygiene,
-        mut cb: impl FnMut(ModPath, &ast::UseTree, /* is_glob */ bool, Option<Name>),
+        mut cb: impl FnMut(ModPath, &ast::UseTree, /* is_glob */ bool, Option<ImportAlias>),
     ) {
         if let Some(tree) = item_src.value.use_tree() {
             lower::lower_use_tree(None, tree, hygiene, &mut cb);

crates/ra_hir_def/src/path/lower/lower_use.rs

@@ -4,20 +4,17 @@
 use std::iter;
 
 use either::Either;
-use hir_expand::{
+use hir_expand::{hygiene::Hygiene, name::AsName};
-    hygiene::Hygiene,
-    name::{AsName, Name},
-};
 use ra_syntax::ast::{self, NameOwner};
 use test_utils::tested_by;
 
-use crate::path::{ModPath, PathKind};
+use crate::path::{ImportAlias, ModPath, PathKind};
 
 pub(crate) fn lower_use_tree(
     prefix: Option<ModPath>,
     tree: ast::UseTree,
     hygiene: &Hygiene,
-    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<Name>),
+    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<ImportAlias>),
 ) {
     if let Some(use_tree_list) = tree.use_tree_list() {
         let prefix = match tree.path() {
@@ -34,7 +31,11 @@ pub(crate) fn lower_use_tree(
             lower_use_tree(prefix.clone(), child_tree, hygiene, cb);
         }
     } else {
-        let alias = tree.alias().and_then(|a| a.name()).map(|a| a.as_name());
+        let alias = tree.alias().map(|a| {
+            a.name()
+                .map(|it| it.as_name())
+                .map_or(ImportAlias::Underscore, |a| ImportAlias::Alias(a))
+        });
         let is_glob = tree.has_star();
         if let Some(ast_path) = tree.path() {
             // Handle self in a path.