Deduplicate tuple indices for completion

Author: lowr

crates/ide-completion/src/completions/dot.rs

@@ -113,8 +113,12 @@ fn complete_fields(
             }
         }
         for (i, ty) in receiver.tuple_fields(ctx.db).into_iter().enumerate() {
-            // Tuple fields are always public (tuple struct fields are handled above).
-            tuple_index(acc, i, ty);
+            // Tuples are always the last type in a deref chain, so just check if the name is
+            // already seen without inserting into the hashset.
+            if !seen_names.contains(&hir::Name::new_tuple_field(i)) {
+                // Tuple fields are always public (tuple struct fields are handled above).
+                tuple_index(acc, i, ty);
+            }
         }
     }
 }
@@ -720,6 +724,28 @@ fn test(a: A) {
         );
     }
 
+    #[test]
+    fn test_tuple_struct_deref_to_tuple_no_same_index() {
+        check(
+            r#"
+//- minicore: deref
+struct A(u8);
+impl core::ops::Deref for A {
+    type Target = (u16, u32);
+    fn deref(&self) -> &Self::Target { loop {} }
+}
+fn test(a: A) {
+    a.$0
+}
+"#,
+            expect![[r#"
+                fd 0                      u8
+                fd 1                      u32
+                me deref() (use core::ops::Deref) fn(&self) -> &<Self as Deref>::Target
+            "#]],
+        );
+    }
+
     #[test]
     fn test_completion_works_in_consts() {
         check(