Don't unify within a reference

If we are expecting a `&Foo` and get a `&something`, when checking the
`something`, we are *expecting* a `Foo`, but we shouldn't try to unify whatever
we get with that expectation, because it could actually be a `&Foo`, and `&&Foo`
coerces to `&Foo`. So this fixes quite a few false type mismatches.

3 files changed, 72 insertions, 11 deletions

diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 1e78f6efd..b8df27706 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -201,7 +201,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
             Expr::Return { expr } => {
                 if let Some(expr) = expr {
-                    self.infer_expr(*expr, &Expectation::has_type(self.return_ty.clone()));
+                    self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
                 }
                 Ty::simple(TypeCtor::Never)
             }
@@ -245,7 +245,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 ty
             }
             Expr::Field { expr, name } => {
-                let receiver_ty = self.infer_expr(*expr, &Expectation::none());
+                let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
                 let ty = autoderef::autoderef(
                     self.db,
@@ -280,7 +280,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 self.normalize_associated_types_in(ty)
             }
             Expr::Await { expr } => {
-                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 let ty = match self.resolve_future_future_output() {
                     Some(future_future_output_alias) => {
                         let ty = self.table.new_type_var();
@@ -299,7 +299,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 ty
             }
             Expr::Try { expr } => {
-                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 let ty = match self.resolve_ops_try_ok() {
                     Some(ops_try_ok_alias) => {
                         let ty = self.table.new_type_var();
@@ -318,7 +318,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 ty
             }
             Expr::Cast { expr, type_ref } => {
-                let _inner_ty = self.infer_expr(*expr, &Expectation::none());
+                let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 let cast_ty = self.make_ty(type_ref);
                 // FIXME check the cast...
                 cast_ty
@@ -334,12 +334,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     } else {
                         Expectation::none()
                     };
-                // FIXME reference coercions etc.
-                let inner_ty = self.infer_expr(*expr, &expectation);
+                let inner_ty = self.infer_expr_inner(*expr, &expectation);
                 Ty::apply_one(TypeCtor::Ref(*mutability), inner_ty)
             }
             Expr::Box { expr } => {
-                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 if let Some(box_) = self.resolve_boxed_box() {
                     Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
                 } else {
@@ -347,7 +346,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
             }
             Expr::UnaryOp { expr, op } => {
-                let inner_ty = self.infer_expr(*expr, &Expectation::none());
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
                 match op {
                     UnaryOp::Deref => match self.resolver.krate() {
                         Some(krate) => {
@@ -417,7 +416,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 _ => Ty::Unknown,
             },
             Expr::Range { lhs, rhs, range_type } => {
-                let lhs_ty = lhs.map(|e| self.infer_expr(e, &Expectation::none()));
+                let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
                 let rhs_expect = lhs_ty
                     .as_ref()
                     .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
@@ -455,7 +454,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
             }
             Expr::Index { base, index } => {
-                let _base_ty = self.infer_expr(*base, &Expectation::none());
+                let _base_ty = self.infer_expr_inner(*base, &Expectation::none());
                 let _index_ty = self.infer_expr(*index, &Expectation::none());
                 // FIXME: use `std::ops::Index::Output` to figure out the real return type
                 Ty::Unknown
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index 9f373a8f4..f1b67555f 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -50,6 +50,10 @@ fn type_at(content: &str) -> String {
 }
 
 fn infer(content: &str) -> String {
+    infer_with_mismatches(content, false)
+}
+
+fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
     let (db, file_id) = TestDB::with_single_file(content);
 
     let mut acc = String::new();
@@ -57,6 +61,7 @@ fn infer(content: &str) -> String {
     let mut infer_def = |inference_result: Arc<InferenceResult>,
                          body_source_map: Arc<BodySourceMap>| {
         let mut types = Vec::new();
+        let mut mismatches = Vec::new();
 
         for (pat, ty) in inference_result.type_of_pat.iter() {
             let syntax_ptr = match body_source_map.pat_syntax(pat) {
@@ -76,6 +81,9 @@ fn infer(content: &str) -> String {
                 None => continue,
             };
             types.push((syntax_ptr, ty));
+            if let Some(mismatch) = inference_result.type_mismatch_for_expr(expr) {
+                mismatches.push((syntax_ptr, mismatch));
+            }
         }
 
         // sort ranges for consistency
@@ -101,6 +109,24 @@ fn infer(content: &str) -> String {
             )
             .unwrap();
         }
+        if include_mismatches {
+            mismatches.sort_by_key(|(src_ptr, _)| {
+                (src_ptr.value.range().start(), src_ptr.value.range().end())
+            });
+            for (src_ptr, mismatch) in &mismatches {
+                let range = src_ptr.value.range();
+                let macro_prefix = if src_ptr.file_id != file_id.into() { "!" } else { "" };
+                write!(
+                    acc,
+                    "{}{}: expected {}, got {}\n",
+                    macro_prefix,
+                    range,
+                    mismatch.expected.display(&db),
+                    mismatch.actual.display(&db),
+                )
+                .unwrap();
+            }
+        }
     };
 
     let module = db.module_for_file(file_id);
diff --git a/crates/ra_hir_ty/src/tests/coercion.rs b/crates/ra_hir_ty/src/tests/coercion.rs
index 1530fcc63..58b22396f 100644
--- a/crates/ra_hir_ty/src/tests/coercion.rs
+++ b/crates/ra_hir_ty/src/tests/coercion.rs
@@ -1,3 +1,4 @@
+use super::infer_with_mismatches;
 use insta::assert_snapshot;
 use test_utils::covers;
 
@@ -367,3 +368,38 @@ fn test() {
     "###
     );
 }
+
+#[test]
+fn coerce_autoderef() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+struct Foo;
+fn takes_ref_foo(x: &Foo) {}
+fn test() {
+    takes_ref_foo(&Foo);
+    takes_ref_foo(&&Foo);
+    takes_ref_foo(&&&Foo);
+}
+"#, true),
+        @r###"
+    [30; 31) 'x': &Foo
+    [39; 41) '{}': ()
+    [52; 133) '{     ...oo); }': ()
+    [58; 71) 'takes_ref_foo': fn takes_ref_foo(&Foo) -> ()
+    [58; 77) 'takes_...(&Foo)': ()
+    [72; 76) '&Foo': &Foo
+    [73; 76) 'Foo': Foo
+    [83; 96) 'takes_ref_foo': fn takes_ref_foo(&Foo) -> ()
+    [83; 103) 'takes_...&&Foo)': ()
+    [97; 102) '&&Foo': &&Foo
+    [98; 102) '&Foo': &Foo
+    [99; 102) 'Foo': Foo
+    [109; 122) 'takes_ref_foo': fn takes_ref_foo(&Foo) -> ()
+    [109; 130) 'takes_...&&Foo)': ()
+    [123; 129) '&&&Foo': &&&Foo
+    [124; 129) '&&Foo': &&Foo
+    [125; 129) '&Foo': &Foo
+    [126; 129) 'Foo': Foo
+    "###
+    );
+}