Merge #1286

1286: Add infer for generic default type r=flodiebold a=edwin0cheng

This PR add infer support for generic default type:

```
struct Gen<T=u32> {
    val: T
}
```

* add the (unresolved) defaults from the definition to GenericParams
* add a query generic_defaults that resolves those defaults to types and returns a Substs
* add the missing type in `substs_from_path_segment`
* add tests

based on the idea in this [comment](https://github.com/rust-analyzer/rust-analyzer/issues/1099#issuecomment-484206279)

Co-authored-by: Edwin Cheng <[email protected]>

1 files changed, 29 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index f8364203d..cd24faba5 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -1449,6 +1449,35 @@ fn test() {
 }
 
 #[test]
+fn infer_associated_method_generics_with_default_param() {
+    assert_snapshot_matches!(
+        infer(r#"
+struct Gen<T=u32> {
+    val: T
+}
+
+impl<T> Gen<T> {
+    pub fn make() -> Gen<T> {
+        loop { }
+    }
+}
+
+fn test() {
+    let a = Gen::make();
+}
+"#),
+        @r###"
+[80; 104) '{     ...     }': !
+[90; 98) 'loop { }': !
+[95; 98) '{ }': ()
+[118; 146) '{     ...e(); }': ()
+[128; 129) 'a': Gen<u32>
+[132; 141) 'Gen::make': fn make<u32>() -> Gen<T>
+[132; 143) 'Gen::make()': Gen<u32>"###
+    );
+}
+
+#[test]
 fn infer_associated_method_generics_without_args() {
     assert_snapshot_matches!(
         infer(r#"