Add method resolution deref inference var test

Author: Veykril

crates/hir-ty/src/infer/expr.rs

@@ -312,15 +312,13 @@ impl InferenceContext<'_> {
             Expr::Call { callee, args, .. } => {
                 let callee_ty = self.infer_expr(*callee, &Expectation::none());
                 let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone(), false);
-                let (res, derefed_callee) = 'b: {
-                    // manual loop to be able to access `derefs.table`
-                    while let Some((callee_deref_ty, _)) = derefs.next() {
-                        let res = derefs.table.callable_sig(&callee_deref_ty, args.len());
-                        if res.is_some() {
-                            break 'b (res, callee_deref_ty);
-                        }
+                let (res, derefed_callee) = loop {
+                    let Some((callee_deref_ty, _)) = derefs.next() else {
+                        break (None, callee_ty.clone());
+                    };
+                    if let Some(res) = derefs.table.callable_sig(&callee_deref_ty, args.len()) {
+                        break (Some(res), callee_deref_ty);
                     }
-                    (None, callee_ty.clone())
                 };
                 // if the function is unresolved, we use is_varargs=true to
                 // suppress the arg count diagnostic here

crates/hir-ty/src/infer/unify.rs

@@ -289,14 +289,14 @@ impl<'a> InferenceTable<'a> {
     }
 
     fn fallback_value(&self, iv: InferenceVar, kind: TyVariableKind) -> Ty {
+        let is_diverging = self
+            .type_variable_table
+            .get(iv.index() as usize)
+            .map_or(false, |data| data.contains(TypeVariableFlags::DIVERGING));
+        if is_diverging {
+            return TyKind::Never.intern(Interner);
+        }
         match kind {
-            _ if self
-                .type_variable_table
-                .get(iv.index() as usize)
-                .map_or(false, |data| data.contains(TypeVariableFlags::DIVERGING)) =>
-            {
-                TyKind::Never
-            }
             TyVariableKind::General => TyKind::Error,
             TyVariableKind::Integer => TyKind::Scalar(Scalar::Int(IntTy::I32)),
             TyVariableKind::Float => TyKind::Scalar(Scalar::Float(FloatTy::F64)),
@@ -438,6 +438,7 @@ impl<'a> InferenceTable<'a> {
     where
         T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
     {
+        // TODO check this vec here
         self.resolve_with_fallback_inner(&mut Vec::new(), t, &fallback)
     }
 
@@ -798,7 +799,7 @@ impl<'a> InferenceTable<'a> {
         let trait_data = self.db.trait_data(fn_once_trait);
         let output_assoc_type = trait_data.associated_type_by_name(&name![Output])?;
 
-        let mut arg_tys = vec![];
+        let mut arg_tys = Vec::with_capacity(num_args);
         let arg_ty = TyBuilder::tuple(num_args)
             .fill(|it| {
                 let arg = match it {

crates/hir-ty/src/tests/method_resolution.rs

@@ -1795,6 +1795,21 @@ fn test() {
     );
 }
 
+#[test]
+fn deref_into_inference_var() {
+    check_types(
+        r#"
+//- minicore:deref
+struct A<T>(T);
+impl core::ops::Deref for A<u32> {}
+impl A<i32> { fn foo(&self) {} }
+fn main() {
+    A(0).foo();
+  //^^^^^^^^^^ ()
+}
+"#,
+    );
+}
 #[test]
 fn receiver_adjustment_autoref() {
     check(