Merge #815

815: Fix another crash r=matklad a=flodiebold

Found while typechecking rustc with better name resolution...

`walk_mut` doing a preorder walk can lead to an infinite recursion when substituting type parameters; postorder is actually what we want.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>

crates/ra_hir/src/ty.rs

@@ -450,7 +450,6 @@ impl Ty {
     }
 
     pub fn walk(&self, f: &mut impl FnMut(&Ty)) {
-        f(self);
         match self {
             Ty::Slice(t) | Ty::Array(t) => t.walk(f),
             Ty::RawPtr(t, _) => t.walk(f),
@@ -490,10 +489,10 @@ impl Ty {
             | Ty::Infer(_)
             | Ty::Unknown => {}
         }
+        f(self);
     }
 
     fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) {
-        f(self);
         match self {
             Ty::Slice(t) | Ty::Array(t) => Arc::make_mut(t).walk_mut(f),
             Ty::RawPtr(t, _) => Arc::make_mut(t).walk_mut(f),
@@ -544,6 +543,7 @@ impl Ty {
             | Ty::Infer(_)
             | Ty::Unknown => {}
         }
+        f(self);
     }
 
     fn fold(mut self, f: &mut impl FnMut(Ty) -> Ty) -> Ty {

crates/ra_hir/src/ty/snapshots/tests__infer_nested_generics_crash.snap

@@ -0,0 +1,12 @@
+---
+created: "2019-02-11T21:59:04.302375838Z"
+creator: insta@0.6.1
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[92; 106) 'query_response': Canonical<QueryResponse<R>>
+[137; 167) '{     ...lue; }': ()
+[143; 164) '&query....value': &QueryResponse<R>
+[144; 158) 'query_response': Canonical<QueryResponse<R>>
+[144; 164) 'query_....value': QueryResponse<R>
+

crates/ra_hir/src/ty/tests.rs

@@ -719,6 +719,25 @@ fn extra_compiler_flags() {
     );
 }
 
+#[test]
+fn infer_nested_generics_crash() {
+    // another crash found typechecking rustc
+    check_inference(
+        "infer_nested_generics_crash",
+        r#"
+struct Canonical<V> {
+    value: V,
+}
+struct QueryResponse<V> {
+    value: V,
+}
+fn test<R>(query_response: Canonical<QueryResponse<R>>) {
+    &query_response.value;
+}
+"#,
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.parse(file_id);