fix(lsp): Correct use argument label code_action with inferred funcs (#2283)

Author: spotandjake

compiler/src/language_server/code_action.re

@@ -96,16 +96,16 @@ let rec process_explicit_type_annotation =
 
 let rec process_named_arg_label = (uri, results: list(Sourcetree.node)) => {
   switch (results) {
-  | [Argument({arg_label, label_specified, loc}), ..._] when !label_specified =>
+  | [
+      Argument({
+        arg_label: Labeled({txt}) | Default({txt}),
+        label_specified: false,
+        loc,
+      }),
+      ..._,
+    ] =>
     let loc = {...loc, loc_end: loc.loc_start};
-    let arg_label =
-      switch (arg_label) {
-      | Unlabeled =>
-        failwith("Impossible: unlabeled argument after typechecking")
-      | Labeled({txt})
-      | Default({txt}) => txt
-      };
-    Some(named_arg_label(Utils.loc_to_range(loc), uri, arg_label));
+    Some(named_arg_label(Utils.loc_to_range(loc), uri, txt));
   | [_, ...rest] => process_named_arg_label(uri, rest)
   | _ => None
   };

compiler/test/suites/grainlsp.re

@@ -351,6 +351,41 @@ f(x="x")
     `Null,
   );
 
+  assertLspOutput(
+    "code_action_add_function_label_pattern",
+    "file:///a.gr",
+    {|module A
+let f = ((a, b)) => a + b
+f((1, 2))
+    |},
+    lsp_input(
+      "textDocument/codeAction",
+      `Assoc([
+        ("textDocument", `Assoc([("uri", `String("file:///a.gr"))])),
+        ("range", lsp_range((2, 2), (2, 2))),
+        ("context", `Assoc([("diagnostics", `List([]))])),
+      ]),
+    ),
+    `Null,
+  );
+
+  assertLspOutput(
+    "code_action_add_function_inferred",
+    "file:///a.gr",
+    {|module A
+a => {a(1); void}
+    |},
+    lsp_input(
+      "textDocument/codeAction",
+      `Assoc([
+        ("textDocument", `Assoc([("uri", `String("file:///a.gr"))])),
+        ("range", lsp_range((1, 8), (1, 8))),
+        ("context", `Assoc([("diagnostics", `List([]))])),
+      ]),
+    ),
+    `Null,
+  );
+
   assertLspOutput(
     "code_action_remove_function_block_braces_1",
     "file:///a.gr",