Merge #11444

11444: feat: Fix up syntax errors in attribute macro inputs to make completion work more often r=flodiebold a=flodiebold

This implements the "fix up syntax nodes" workaround mentioned in #11014. It isn't much more than a proof of concept; I have only implemented a few cases, but it already helps quite a bit.

Some notes:
 - I'm not super happy about how much the fixup procedure needs to interact with the syntax node -> token tree conversion code (e.g. needing to share the token map). This could maybe be simplified with some refactoring of that code.
 - It would maybe be nice to have the fixup procedure reuse or share information with the parser, though I'm not really sure how much that would actually help.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>

crates/hir_def/src/macro_expansion_tests.rs

@@ -14,10 +14,10 @@ mod builtin_fn_macro;
 mod builtin_derive_macro;
 mod proc_macros;
 
-use std::{iter, ops::Range};
+use std::{iter, ops::Range, sync::Arc};
 
 use ::mbe::TokenMap;
-use base_db::{fixture::WithFixture, SourceDatabase};
+use base_db::{fixture::WithFixture, ProcMacro, SourceDatabase};
 use expect_test::Expect;
 use hir_expand::{
     db::{AstDatabase, TokenExpander},
@@ -39,7 +39,21 @@ use crate::{
 
 #[track_caller]
 fn check(ra_fixture: &str, mut expect: Expect) {
-    let db = TestDB::with_files(ra_fixture);
+    let extra_proc_macros = vec![(
+        r#"
+#[proc_macro_attribute]
+pub fn identity_when_valid(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    item
+}
+"#
+        .into(),
+        ProcMacro {
+            name: "identity_when_valid".into(),
+            kind: base_db::ProcMacroKind::Attr,
+            expander: Arc::new(IdentityWhenValidProcMacroExpander),
+        },
+    )];
+    let db = TestDB::with_files_extra_proc_macros(ra_fixture, extra_proc_macros);
     let krate = db.crate_graph().iter().next().unwrap();
     let def_map = db.crate_def_map(krate);
     let local_id = def_map.root();
@@ -172,7 +186,7 @@ fn check(ra_fixture: &str, mut expect: Expect) {
         let range: Range<usize> = range.into();
 
         if show_token_ids {
-            if let Some((tree, map)) = arg.as_deref() {
+            if let Some((tree, map, _)) = arg.as_deref() {
                 let tt_range = call.token_tree().unwrap().syntax().text_range();
                 let mut ranges = Vec::new();
                 extract_id_ranges(&mut ranges, &map, &tree);
@@ -201,10 +215,19 @@ fn check(ra_fixture: &str, mut expect: Expect) {
     }
 
     for decl_id in def_map[local_id].scope.declarations() {
-        if let ModuleDefId::AdtId(AdtId::StructId(struct_id)) = decl_id {
-            let src = struct_id.lookup(&db).source(&db);
+        // FIXME: I'm sure there's already better way to do this
+        let src = match decl_id {
+            ModuleDefId::AdtId(AdtId::StructId(struct_id)) => {
+                Some(struct_id.lookup(&db).source(&db).syntax().cloned())
+            }
+            ModuleDefId::FunctionId(function_id) => {
+                Some(function_id.lookup(&db).source(&db).syntax().cloned())
+            }
+            _ => None,
+        };
+        if let Some(src) = src {
             if src.file_id.is_attr_macro(&db) || src.file_id.is_custom_derive(&db) {
-                let pp = pretty_print_macro_expansion(src.value.syntax().clone(), None);
+                let pp = pretty_print_macro_expansion(src.value, None);
                 format_to!(expanded_text, "\n{}", pp)
             }
         }
@@ -304,3 +327,25 @@ fn pretty_print_macro_expansion(expn: SyntaxNode, map: Option<&TokenMap>) -> Str
     }
     res
 }
+
+// Identity mapping, but only works when the input is syntactically valid. This
+// simulates common proc macros that unnecessarily parse their input and return
+// compile errors.
+#[derive(Debug)]
+struct IdentityWhenValidProcMacroExpander;
+impl base_db::ProcMacroExpander for IdentityWhenValidProcMacroExpander {
+    fn expand(
+        &self,
+        subtree: &Subtree,
+        _: Option<&Subtree>,
+        _: &base_db::Env,
+    ) -> Result<Subtree, base_db::ProcMacroExpansionError> {
+        let (parse, _) =
+            ::mbe::token_tree_to_syntax_node(subtree, ::mbe::TopEntryPoint::MacroItems);
+        if parse.errors().is_empty() {
+            Ok(subtree.clone())
+        } else {
+            panic!("got invalid macro input: {:?}", parse.errors());
+        }
+    }
+}

crates/hir_def/src/macro_expansion_tests/proc_macros.rs

@@ -52,3 +52,43 @@ struct S;
 #[attr2] struct S;"##]],
     );
 }
+
+#[test]
+fn attribute_macro_syntax_completion_1() {
+    // this is just the case where the input is actually valid
+    check(
+        r#"
+//- proc_macros: identity_when_valid
+#[proc_macros::identity_when_valid]
+fn foo() { bar.baz(); blub }
+"#,
+        expect![[r##"
+#[proc_macros::identity_when_valid]
+fn foo() { bar.baz(); blub }
+
+fn foo() {
+    bar.baz();
+    blub
+}"##]],
+    );
+}
+
+#[test]
+fn attribute_macro_syntax_completion_2() {
+    // common case of dot completion while typing
+    check(
+        r#"
+//- proc_macros: identity_when_valid
+#[proc_macros::identity_when_valid]
+fn foo() { bar.; blub }
+"#,
+        expect![[r##"
+#[proc_macros::identity_when_valid]
+fn foo() { bar.; blub }
+
+fn foo() {
+    bar. ;
+    blub
+}"##]],
+    );
+}