Add comment and mark

crates/ra_hir/src/marks.rs

@@ -3,4 +3,5 @@ test_utils::marks!(
     item_map_enum_importing
     type_var_cycles_resolve_completely
     type_var_cycles_resolve_as_possible
+    type_var_resolves_to_int_var
 );

crates/ra_hir/src/ty.rs

@@ -1003,8 +1003,13 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     /// otherwise, return ty.
     fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
         let mut ty = Cow::Borrowed(ty);
-        for _ in 0..3 {
-            // the type variable could resolve to a int/float variable
+        // The type variable could resolve to a int/float variable. Hence try
+        // resolving up to three times; each type of variable shouldn't occur
+        // more than once
+        for i in 0..3 {
+            if i > 0 {
+                tested_by!(type_var_resolves_to_int_var);
+            }
             match &*ty {
                 Ty::Infer(tv) => {
                     let inner = tv.to_inner();
@@ -1019,6 +1024,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 _ => return ty,
             }
         }
+        log::error!("Inference variable still not resolved: {:?}", ty);
         ty
     }
 

crates/ra_hir/src/ty/tests.rs

@@ -652,6 +652,7 @@ fn write() {
 
 #[test]
 fn infer_std_crash_2() {
+    covers!(type_var_resolves_to_int_var);
     // caused "equating two type variables, ...", taken from std
     check_inference(
         "infer_std_crash_2",