Implement type variables

This will really become necessary when we implement generics, but even now, it
allows us to reason 'backwards' to infer types of expressions that we didn't
understand for some reason.

We use ena, the union-find implementation extracted from rustc, to keep track of
type variables.

1 files changed, 21 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index a76925b58..93bf431c4 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -113,6 +113,27 @@ fn test(a: &u32, b: &mut u32, c: *const u32, d: *mut u32) {
     );
 }
 
+#[test]
+fn infer_backwards() {
+    check_inference(
+        r#"
+fn takes_u32(x: u32) {}
+
+struct S { i32_field: i32 }
+
+fn test() -> &mut &f64 {
+    let a = unknown_function();
+    takes_u32(a);
+    let b = unknown_function();
+    S { i32_field: b };
+    let c = unknown_function();
+    &mut &c
+}
+"#,
+        "0006_backwards.txt",
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.source_file(file_id);