Repository: rust-lang/rust-analyzer
Pull request #17511 (2024-06-29 10:40:17)

#17497 - Invalid RA diagnostic error: expected 2 arguments, found 1
Fix for #17497

The issue occurs because in some configurations of traits where one of them has `Deref` as a supertrait, RA's type inference algorithm fails to resolve the `Deref::Target` type, and instead uses a `TyKind::BoundVar` (i.e. an unknown type). This "autoderefed" type then incorrectly acts as if it implements all traits in scope.

The fix is to re-apply the same sanity-check that is done in [`iterate_method_candidates_with_autoref()`](https://github.com/rust-lang/rust-analyzer/blob/9463d9eea4b87e651e7d8ed8425a9c92f23b1cdf/crates/hir-ty/src/method_resolution.rs#L1008), that is: don't try to resolve methods on unknown types. This same sanity-check is now done on each autoderefed type for which trait methods are about to be checked. If the autoderefed type is unknown, then the iterating of the trait methods for that type is skipped.

Includes a unit test that only passes after applying the fixes in this commit.

Includes a change to the assertion count in test `syntax_highlighting::tests::benchmark_syntax_highlighting_parser` as suggested by Lukas Wirth during review.

Includes a change to the sanity-check code as suggested by Florian Diebold during review.

lnicola: r? @flodiebold 

Patch:
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index c07bd08be4..8ba8071d36 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -30,8 +30,8 @@ use crate::{
     utils::all_super_traits,
     AdtId, Canonical, CanonicalVarKinds, DebruijnIndex, DynTyExt, ForeignDefId, GenericArgData,
     Goal, Guidance, InEnvironment, Interner, Mutability, Scalar, Solution, Substitution,
-    TraitEnvironment, TraitRef, TraitRefExt, Ty, TyBuilder, TyExt, TyKind, VariableKind,
-    WhereClause,
+    TraitEnvironment, TraitRef, TraitRefExt, Ty, TyBuilder, TyExt, TyKind, TyVariableKind,
+    VariableKind, WhereClause,
 };
 
 /// This is used as a key for indexing impls.
@@ -1083,6 +1083,11 @@ fn iterate_method_candidates_by_receiver(
     table.run_in_snapshot(|table| {
         let mut autoderef = autoderef::Autoderef::new(table, receiver_ty.clone(), true);
         while let Some((self_ty, _)) = autoderef.next() {
+            if matches!(self_ty.kind(Interner), TyKind::InferenceVar(_, TyVariableKind::General)) {
+                // don't try to resolve methods on unknown types
+                return ControlFlow::Continue(());
+            }
+
             iterate_trait_method_candidates(
                 &self_ty,
                 autoderef.table,


Test patch:
diff --git a/crates/hir-ty/src/tests/method_resolution.rs b/crates/hir-ty/src/tests/method_resolution.rs
index 360a129283..14e2e74653 100644
--- a/crates/hir-ty/src/tests/method_resolution.rs
+++ b/crates/hir-ty/src/tests/method_resolution.rs
@@ -2099,3 +2099,42 @@ fn test() {
 "#,
     );
 }
+
+#[test]
+fn mismatched_args_due_to_supertraits_with_deref() {
+    check_no_mismatches(
+        r#"
+//- minicore: deref
+use core::ops::Deref;
+
+trait Trait1 {
+    type Assoc: Deref<Target = String>;
+}
+
+trait Trait2: Trait1 {
+}
+
+trait Trait3 {
+    type T1: Trait1;
+    type T2: Trait2;
+    fn bar(&self, x: bool, y: bool);
+}
+
+struct Foo;
+
+impl Foo {
+    fn bar(&mut self, _: &'static str) {}
+}
+
+impl Deref for Foo {
+    type Target = u32;
+    fn deref(&self) -> &Self::Target { &0 }
+}
+
+fn problem_method<T: Trait3>() {
+    let mut foo = Foo;
+    foo.bar("hello"); // Rustc ok, RA errors (mismatched args)
+}
+"#,
+    );
+}
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 5f711600a2..2070022d41 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -1238,7 +1238,7 @@ fn benchmark_syntax_highlighting_parser() {
             })
             .count()
     };
-    assert_eq!(hash, 1169);
+    assert_eq!(hash, 1167);
 }
 
 #[test]