implement initial type inference for index expressions

2 files changed, 20 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index 33bfd0952..cca59538a 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -1279,6 +1279,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
                 _ => Ty::Unknown,
             },
+            Expr::Index { base, index } => {
+                let _base_ty = self.infer_expr(*base, &Expectation::none());
+                let _index_ty = self.infer_expr(*index, &Expectation::none());
+                // FIXME: use `std::ops::Index::Output` to figure out the real return type
+                Ty::Unknown
+            }
             Expr::Tuple { exprs } => {
                 let mut ty_vec = Vec::with_capacity(exprs.len());
                 for arg in exprs.iter() {
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 28727bb18..6c2d857bc 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -2656,6 +2656,20 @@ fn test() -> u64 {
 }
 
 #[test]
+fn indexing_arrays() {
+    assert_snapshot_matches!(
+        infer("fn main() { &mut [9][2]; }"),
+        @r###"
+[10; 26) '{ &mut...[2]; }': ()
+[12; 23) '&mut [9][2]': &mut {unknown}
+[17; 20) '[9]': [i32;_]
+[17; 23) '[9][2]': {unknown}
+[18; 19) '9': i32
+[21; 22) '2': i32"###
+    )
+}
+
+#[test]
 fn infer_macros_expanded() {
     assert_snapshot_matches!(
         infer(r#"