Implement LUB coercion of array elements

Author: jonas-schievink

crates/hir_ty/src/infer/expr.rs

@@ -729,7 +729,7 @@ impl<'a> InferenceContext<'a> {
                 TyKind::Tuple(tys.len(), Substitution::from_iter(&Interner, tys)).intern(&Interner)
             }
             Expr::Array(array) => {
-                let elem_ty =
+                let mut elem_ty =
                     match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(&Interner)) {
                         Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
                         _ => self.table.new_type_var(),
@@ -738,8 +738,8 @@ impl<'a> InferenceContext<'a> {
                 let len = match array {
                     Array::ElementList(items) => {
                         for expr in items.iter() {
-                            // FIXME: use CoerceMany (coerce_merge_branch)
-                            self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
+                            let cur_elem_ty = self.infer_expr_inner(*expr, expected);
+                            elem_ty = self.coerce_merge_branch(Some(*expr), &elem_ty, &cur_elem_ty);
                         }
                         Some(items.len() as u64)
                     }

crates/hir_ty/src/tests/coercion.rs

@@ -507,3 +507,17 @@ fn main() {
         "#,
     );
 }
+
+#[test]
+fn coerce_array_elems_lub() {
+    check_no_mismatches(
+        r#"
+fn f() {}
+fn g() {}
+
+fn test() {
+    [f, g];
+}
+        "#,
+    );
+}

crates/hir_ty/src/tests/regression.rs

@@ -117,19 +117,19 @@ fn recursive_vars_2() {
         "#,
         expect![[r#"
             10..79 '{     ...x)]; }': ()
-            20..21 'x': &{unknown}
-            24..31 'unknown': &{unknown}
+            20..21 'x': {unknown}
+            24..31 'unknown': {unknown}
             41..42 'y': {unknown}
             45..52 'unknown': {unknown}
-            58..76 '[(x, y..., &x)]': [(&{unknown}, {unknown}); 2]
-            59..65 '(x, y)': (&{unknown}, {unknown})
-            60..61 'x': &{unknown}
+            58..76 '[(x, y..., &x)]': [({unknown}, {unknown}); 2]
+            59..65 '(x, y)': ({unknown}, {unknown})
+            60..61 'x': {unknown}
             63..64 'y': {unknown}
-            67..75 '(&y, &x)': (&{unknown}, {unknown})
+            67..75 '(&y, &x)': (&{unknown}, &{unknown})
             68..70 '&y': &{unknown}
             69..70 'y': {unknown}
-            72..74 '&x': &&{unknown}
-            73..74 'x': &{unknown}
+            72..74 '&x': &{unknown}
+            73..74 'x': {unknown}
         "#]],
     );
 }