Merge #892

892: Type aliases r=matklad a=flodiebold

This implements type aliases (i.e. `type` definitions).

There's just one snag: handling recursion. E.g. `type Foo = Foo` makes type inference panic with a query cycle. I think the best way to handle this would be if Salsa provided the ability to catch cycle errors? It seems that there's some work underway to support this [here](https://github.com/salsa-rs/salsa/issues/6) and [here](https://github.com/salsa-rs/salsa/pull/147). Should we wait for this? I don't see a good way to handle this without help from Salsa.

Co-authored-by: Florian Diebold <[email protected]>

1 files changed, 23 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/snapshots/tests__infer_type_alias.snap b/crates/ra_hir/src/ty/snapshots/tests__infer_type_alias.snap
new file mode 100644
index 000000000..241c08353
--- /dev/null
+++ b/crates/ra_hir/src/ty/snapshots/tests__infer_type_alias.snap
@@ -0,0 +1,23 @@
+---
+created: "2019-02-24T16:13:47.561870283Z"
+creator: [email protected]
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[117; 118) 'x': A<u32, i128>
+[125; 126) 'y': A<&str, u128>
+[139; 140) 'z': A<u8, i8>
+[155; 212) '{     ...z.y; }': ()
+[161; 162) 'x': A<u32, i128>
+[161; 164) 'x.x': u32
+[170; 171) 'x': A<u32, i128>
+[170; 173) 'x.y': i128
+[179; 180) 'y': A<&str, u128>
+[179; 182) 'y.x': &str
+[188; 189) 'y': A<&str, u128>
+[188; 191) 'y.y': u128
+[197; 198) 'z': A<u8, i8>
+[197; 200) 'z.x': u8
+[206; 207) 'z': A<u8, i8>
+[206; 209) 'z.y': i8
+