Disable redundant type annotation

CHANGES.md

@@ -3,6 +3,9 @@
 ## Fixes
 
 - Fix a document syncing issue when utf-16 is the position encoding (#1004)
+- Disable "Type-annotate" action for code that is already annotated.
+  ([#1037](https://github.com/ocaml/ocaml-lsp/pull/1037)), fixes
+  [#1036](https://github.com/ocaml/ocaml-lsp/issues/1036)
 
 # 1.15.1
 

ocaml-lsp-server/src/code_actions/action_type_annotate.ml

@@ -7,8 +7,22 @@ let check_typeable_context pipeline pos_start =
   let pos_start = Mpipeline.get_lexing_pos pipeline pos_start in
   let typer = Mpipeline.typer_result pipeline in
   let browse = Mbrowse.of_typedtree (Mtyper.get_typedtree typer) in
+  let is_exp_constrained = function
+    | ((Typedtree.Texp_constraint _), _, _) -> true
+    | _ -> false in
+  let is_pat_constrained = function
+    | ((Typedtree.Tpat_constraint _), _, _) -> true
+    | _ -> false in
+  let is_valid p extras =
+    if List.exists ~f:p extras then `Invalid else `Valid in
   match Mbrowse.enclosing pos_start [ browse ] with
-  | (_, (Expression _ | Pattern _)) :: _ -> `Valid
+  | (_, (Expression e)) :: _ ->
+    is_valid is_exp_constrained e.exp_extra
+  | (_, (Pattern { pat_desc = Typedtree.Tpat_any; _ })) ::
+    (_, (Pattern { pat_desc = Typedtree.Tpat_alias _ ; pat_extra; _ })) :: _ ->
+    is_valid is_pat_constrained pat_extra
+  | (_, (Pattern p)) :: _ ->
+    is_valid is_pat_constrained p.pat_extra
   | _ :: _ | [] -> `Invalid
 
 let get_source_text doc (loc : Loc.t) =

ocaml-lsp-server/test/e2e/__tests__/textDocument-codeAction.test.ts

@@ -478,6 +478,76 @@ let f (x : t) = x
     `);
   });
 
+  it("does not type-annotate already annotated argument", async () => {
+    openDocument(
+      outdent`
+let f (x : int) = 1
+`,
+      "file:///test.ml",
+    );
+    let start = Types.Position.create(1, 7);
+    let end = Types.Position.create(1, 8);
+    let actions = await codeAction("file:///test.ml", start, end);
+    expect(actions).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "command": Object {
+            "arguments": Array [
+              "file:///test.mli",
+            ],
+            "command": "ocamllsp/open-related-source",
+            "title": "Create test.mli",
+          },
+          "edit": Object {
+            "documentChanges": Array [
+              Object {
+                "kind": "create",
+                "uri": "file:///test.mli",
+              },
+            ],
+          },
+          "kind": "switch",
+          "title": "Create test.mli",
+        },
+      ]
+    `);
+  });
+
+  it("does not type-annotate already annotated value", async () => {
+    openDocument(
+      outdent`
+let f x = (1 : int)
+`,
+      "file:///test.ml",
+    );
+    let start = Types.Position.create(1, 11);
+    let end = Types.Position.create(1, 12);
+    let actions = await codeAction("file:///test.ml", start, end);
+    expect(actions).toMatchInlineSnapshot(`
+      Array [
+        Object {
+          "command": Object {
+            "arguments": Array [
+              "file:///test.mli",
+            ],
+            "command": "ocamllsp/open-related-source",
+            "title": "Create test.mli",
+          },
+          "edit": Object {
+            "documentChanges": Array [
+              Object {
+                "kind": "create",
+                "uri": "file:///test.mli",
+              },
+            ],
+          },
+          "kind": "switch",
+          "title": "Create test.mli",
+        },
+      ]
+    `);
+  });
+
   it("does not type-annotate in a non expression context", async () => {
     openDocument(
       outdent`