refactor(lsp): shouldShowParameterHints config hook replaces provider patching

TypeScriptSupport monkey-patched its client's getParameterHints to veto
signature help inside callback bodies - fragile and invisible to the
framework. registerLanguageServer now accepts an optional
shouldShowParameterHints(editor) callback (same family as
shouldAutoTrigger / documentFilter / filterDiagnostics): returning false
rejects the request, so the provider stays the request owner - the popup
is suppressed/dismissed with no fall-through to lower-priority providers
(a fallback answering would undo the veto; document-level opt-out via
documentFilter still preserves fall-through). The body-scan policy stays
entirely in the TS extension.

Author: abose

src/extensions/default/TypeScriptSupport/main.js

@@ -351,27 +351,6 @@ define(function (require, exports, module) {
         return false;
     }
 
-    // tsserver treats a whole callback argument INCLUDING its body as "inside the call", so the
-    // parent call's signature would pop up (and, via the cursor-activity refresh, never dismiss)
-    // while coding inside a callback. Rejecting in getParameterHints covers every trigger path -
-    // Ctrl-Space, typed "("/",", and the cursor-activity re-show, which then auto-dismisses an
-    // already-visible popup when the caret enters the body. Rejecting (rather than declining in
-    // hasParameterHints) keeps this provider the owner of the request, so the manager dismisses
-    // the popup instead of falling through to the legacy Tern JS provider. This is vtsls-specific
-    // policy, so it wraps OUR provider here instead of living in the shared LSP framework
-    // (intelephense and pyrefly already answer null inside nested bodies on their own).
-    function _installParameterHintBodyGate(client) {
-        const provider = client.parameterHints;
-        const baseGetParameterHints = provider.getParameterHints.bind(provider);
-        provider.getParameterHints = function (explicit, onCursorActivity) {
-            const editor = EditorManager.getActiveEditor();
-            if (editor && _inFunctionBodyInsideArgs(editor)) {
-                return $.Deferred().reject(null);
-            }
-            return baseGetParameterHints(explicit, onCursorActivity);
-        };
-    }
-
     async function start() {
         if (registered || !canRun()) {
             return;
@@ -390,12 +369,17 @@ define(function (require, exports, module) {
             languages: SUPPORTED_LANGUAGES,
             languageIdMap: LANGUAGE_ID_MAP,
             initializationOptions: INITIALIZATION_OPTIONS,
-            filterDiagnostics: filterDiagnostics
+            filterDiagnostics: filterDiagnostics,
+            // tsserver treats a whole callback argument INCLUDING its body as "inside the call" -
+            // veto signature help there so the parent call's hint doesn't show (or stick around)
+            // while coding inside a callback like `on("x", () => { | })`.
+            shouldShowParameterHints: function (editor) {
+                return !_inFunctionBodyInsideArgs(editor);
+            }
         });
         if (client) {
             registered = true;
             _client = client;
-            _installParameterHintBodyGate(client);
         }
     }
 

src/languageTools/DefaultProviders.js

@@ -720,6 +720,19 @@ define(function (require, exports, module) {
             docPath = editor.document.file._path,
             $deferredHints = $.Deferred();
 
+        // A language server may VETO signature help at specific cursor positions by supplying a
+        // `shouldShowParameterHints(editor)` callback (e.g. vtsls suppresses the parent call's
+        // hint inside callback bodies). Rejecting here (rather than declining in
+        // hasParameterHints) keeps this provider the owner of the request, so the manager
+        // dismisses the popup instead of falling through to a lower-priority provider - and the
+        // cursor-activity refresh then auto-dismisses an already-visible popup when the caret
+        // moves into a vetoed position.
+        var config = this.client.config || {};
+        if (typeof config.shouldShowParameterHints === "function" &&
+                !config.shouldShowParameterHints(editor)) {
+            return $deferredHints.reject(null);
+        }
+
         this.client.requestParameterHints({
             filePath: docPath,
             cursorPos: pos

src/languageTools/LSPClient.js

@@ -835,6 +835,12 @@ define(function (require, exports, module) {
      *        treats the default null answer as "all diagnostics off").
      * @param {function(Array):Array} [config.filterDiagnostics] - server-specific post-filter for
      *        published diagnostics
+     * @param {function(Editor):boolean} [config.shouldShowParameterHints] - per-position VETO for
+     *        signature help: return false to reject the request - the popup is suppressed or
+     *        dismissed there and deliberately does NOT fall through to lower-priority providers
+     *        (a fallback answering would undo the veto). For "this document isn't mine, let
+     *        others serve it" use documentFilter instead - that preserves fall-through. E.g.
+     *        vtsls vetoes the parent call's hint inside nested callback bodies.
      * @param {string} [config.suppressStderrPattern] - regex source (string, not RegExp - it
      *        crosses the node connector); stderr lines matching it are dropped from the live
      *        console log. Opt in for servers that narrate every request on stderr (pyrefly uses