Fix false positive type mismatch in const reference patterns

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

@@ -262,7 +262,7 @@ impl InferenceContext<'_> {
     fn infer_pat(&mut self, pat: PatId, expected: &Ty, mut default_bm: BindingMode) -> Ty {
         let mut expected = self.resolve_ty_shallow(expected);
 
-        if is_non_ref_pat(self.body, pat) {
+        if self.is_non_ref_pat(self.body, pat) {
             let mut pat_adjustments = Vec::new();
             while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
                 pat_adjustments.push(expected.clone());
@@ -496,24 +496,28 @@ impl InferenceContext<'_> {
 
         self.infer_expr(expr, &Expectation::has_type(expected.clone()))
     }
-}
 
-fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
-    match &body[pat] {
-        Pat::Tuple { .. }
-        | Pat::TupleStruct { .. }
-        | Pat::Record { .. }
-        | Pat::Range { .. }
-        | Pat::Slice { .. } => true,
-        Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
-        // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
-        Pat::Path(..) => true,
-        Pat::ConstBlock(..) => true,
-        Pat::Lit(expr) => !matches!(
-            body[*expr],
-            Expr::Literal(Literal::String(..) | Literal::CString(..) | Literal::ByteString(..))
-        ),
-        Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
+    fn is_non_ref_pat(&mut self, body: &hir_def::body::Body, pat: PatId) -> bool {
+        match &body[pat] {
+            Pat::Tuple { .. }
+            | Pat::TupleStruct { .. }
+            | Pat::Record { .. }
+            | Pat::Range { .. }
+            | Pat::Slice { .. } => true,
+            Pat::Or(pats) => pats.iter().all(|p| self.is_non_ref_pat(body, *p)),
+            Pat::Path(p) => {
+                let v = self.resolve_value_path_inner(p, pat.into());
+                v.is_some_and(|x| !matches!(x.0, hir_def::resolver::ValueNs::ConstId(_)))
+            }
+            Pat::ConstBlock(..) => false,
+            Pat::Lit(expr) => !matches!(
+                body[*expr],
+                Expr::Literal(Literal::String(..) | Literal::CString(..) | Literal::ByteString(..))
+            ),
+            Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => {
+                false
+            }
+        }
     }
 }
 

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

@@ -40,33 +40,7 @@ impl InferenceContext<'_> {
     }
 
     fn resolve_value_path(&mut self, path: &Path, id: ExprOrPatId) -> Option<ValuePathResolution> {
-        let (value, self_subst) = if let Some(type_ref) = path.type_anchor() {
-            let last = path.segments().last()?;
-
-            // Don't use `self.make_ty()` here as we need `orig_ns`.
-            let ctx =
-                crate::lower::TyLoweringContext::new(self.db, &self.resolver, self.owner.into());
-            let (ty, orig_ns) = ctx.lower_ty_ext(type_ref);
-            let ty = self.table.insert_type_vars(ty);
-            let ty = self.table.normalize_associated_types_in(ty);
-
-            let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
-            let (ty, _) = ctx.lower_ty_relative_path(ty, orig_ns, remaining_segments_for_ty);
-            let ty = self.table.insert_type_vars(ty);
-            let ty = self.table.normalize_associated_types_in(ty);
-            self.resolve_ty_assoc_item(ty, last.name, id).map(|(it, substs)| (it, Some(substs)))?
-        } else {
-            // FIXME: report error, unresolved first path segment
-            let value_or_partial =
-                self.resolver.resolve_path_in_value_ns(self.db.upcast(), path)?;
-
-            match value_or_partial {
-                ResolveValueResult::ValueNs(it, _) => (it, None),
-                ResolveValueResult::Partial(def, remaining_index, _) => self
-                    .resolve_assoc_item(def, path, remaining_index, id)
-                    .map(|(it, substs)| (it, Some(substs)))?,
-            }
-        };
+        let (value, self_subst) = self.resolve_value_path_inner(path, id)?;
 
         let value_def = match value {
             ValueNs::LocalBinding(pat) => match self.result.type_of_binding.get(pat) {
@@ -144,6 +118,41 @@ impl InferenceContext<'_> {
         Some(ValuePathResolution::GenericDef(value_def, generic_def, substs))
     }
 
+    pub(super) fn resolve_value_path_inner(
+        &mut self,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<chalk_ir::Substitution<Interner>>)> {
+        let (value, self_subst) = if let Some(type_ref) = path.type_anchor() {
+            let last = path.segments().last()?;
+
+            // Don't use `self.make_ty()` here as we need `orig_ns`.
+            let ctx =
+                crate::lower::TyLoweringContext::new(self.db, &self.resolver, self.owner.into());
+            let (ty, orig_ns) = ctx.lower_ty_ext(type_ref);
+            let ty = self.table.insert_type_vars(ty);
+            let ty = self.table.normalize_associated_types_in(ty);
+
+            let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
+            let (ty, _) = ctx.lower_ty_relative_path(ty, orig_ns, remaining_segments_for_ty);
+            let ty = self.table.insert_type_vars(ty);
+            let ty = self.table.normalize_associated_types_in(ty);
+            self.resolve_ty_assoc_item(ty, last.name, id).map(|(it, substs)| (it, Some(substs)))?
+        } else {
+            // FIXME: report error, unresolved first path segment
+            let value_or_partial =
+                self.resolver.resolve_path_in_value_ns(self.db.upcast(), path)?;
+
+            match value_or_partial {
+                ResolveValueResult::ValueNs(it, _) => (it, None),
+                ResolveValueResult::Partial(def, remaining_index, _) => self
+                    .resolve_assoc_item(def, path, remaining_index, id)
+                    .map(|(it, substs)| (it, Some(substs)))?,
+            }
+        };
+        Some((value, self_subst))
+    }
+
     fn add_required_obligations_for_value_path(&mut self, def: GenericDefId, subst: &Substitution) {
         let predicates = self.db.generic_predicates(def);
         for predicate in predicates.iter() {

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

@@ -1153,3 +1153,41 @@ fn main() {
 "#,
     );
 }
+
+#[test]
+fn type_mismatch_pat_const_reference() {
+    check_no_mismatches(
+        r#"
+const TEST_STR: &'static str = "abcd";
+
+fn main() {
+    let s = "abcd";
+    match s {
+        TEST_STR => (),
+        _ => (),
+    }
+}
+
+            "#,
+    );
+    check(
+        r#"
+struct Foo<T>(T);
+
+impl<T> Foo<T> {
+    const TEST_I32_REF: &'static i32 = &3;
+    const TEST_I32: i32 = 3;
+}
+
+fn main() {
+    match &6 {
+        Foo::<i32>::TEST_I32_REF => (),
+        Foo::<i32>::TEST_I32 => (),
+      //^^^^^^^^^^^^^^^^^^^^ expected &i32, got i32
+        _ => (),
+    }
+}
+
+            "#,
+    );
+}