Use correct substs for super trait assoc types

When referring to an associated type of a super trait, we used the substs of the
subtrait. That led to the #4931 crash if the subtrait had less parameters, but
it could also lead to other incorrectness if just the order was different.

Fixes #4931.

1 files changed, 28 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/tests/regression.rs b/crates/ra_hir_ty/src/tests/regression.rs
index ed43df484..8dc5603b7 100644
--- a/crates/ra_hir_ty/src/tests/regression.rs
+++ b/crates/ra_hir_ty/src/tests/regression.rs
@@ -665,3 +665,31 @@ impl Foo<i64> {
     "###
     );
 }
+
+#[test]
+fn issue_4931() {
+    assert_snapshot!(
+        infer(r#"
+trait Div<T> {
+    type Output;
+}
+
+trait CheckedDiv: Div<()> {}
+
+trait PrimInt: CheckedDiv<Output = ()> {
+    fn pow(self);
+}
+
+fn check<T: PrimInt>(i: T) {
+    i.pow();
+}
+"#),
+        @r###"
+    118..122 'self': Self
+    149..150 'i': T
+    155..171 '{     ...w(); }': ()
+    161..162 'i': T
+    161..168 'i.pow()': ()
+    "###
+    );
+}