feat: trigger signature help after call completion (#1878)

Author: renkun-ken

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Accepting a function or method completion that inserts parentheses now opens signature help, respecting `editor.parameterHints.enabled`.
+
 ## 3.2.0 - 2026-10-15
 
 ### Compatibility and upgrade notes

src/completionMiddleware.ts

@@ -0,0 +1,30 @@
+import { CompletionItemKind, SnippetString, workspace } from 'vscode';
+import type { CompletionMiddleware } from 'vscode-languageclient/node';
+
+export const completionMiddleware: CompletionMiddleware = {
+    provideCompletionItem: async (document, position, context, token, next) => {
+        const result = await next(document, position, context, token);
+        if (!result || token.isCancellationRequested
+            || !workspace.getConfiguration('editor', document).get<boolean>('parameterHints.enabled', true)) {
+            return result;
+        }
+
+        const items = Array.isArray(result) ? result : result.items;
+        for (const item of items) {
+            // languageserver inserts a call with the cursor inside its parentheses.
+            // Snippet insertion does not fire VS Code's signature-help triggers.
+            if (!item.command
+                && (item.kind === CompletionItemKind.Function
+                    || item.kind === CompletionItemKind.Method
+                    || item.kind === CompletionItemKind.Constructor)
+                && item.insertText instanceof SnippetString
+                && item.insertText.value.endsWith('($0)')) {
+                item.command = {
+                    title: 'Trigger parameter hints',
+                    command: 'editor.action.triggerParameterHints'
+                };
+            }
+        }
+        return result;
+    }
+};

src/languageService.ts

@@ -12,6 +12,7 @@ import { extensionContext } from './extension';
 import { CommonOptions } from 'child_process';
 import { boundSessionForDocument, onDidBindSessionDocument, Session } from './session';
 import { SessionSignatureHelpProvider } from './signatureHelp';
+import { completionMiddleware } from './completionMiddleware';
 
 export class LanguageService implements Disposable {
     private readonly clients: Map<string, LanguageClient> = new Map();
@@ -170,6 +171,7 @@ export class LanguageService implements Disposable {
                 fileEvents: workspace.createFileSystemWatcher('**/*.{R,r}'),
             },
             middleware: {
+                ...completionMiddleware,
                 provideSignatureHelp: async (document, position, context, token, next) => {
                     const result = await next(document, position, context, token);
                     // An empty LSP result still suppresses other VS Code providers.

src/test/suite/completionMiddleware.test.ts

@@ -0,0 +1,212 @@
+import * as assert from 'assert';
+import * as sinon from 'sinon';
+import { PassThrough } from 'stream';
+import * as vscode from 'vscode';
+import * as lsp from 'vscode-languageclient/node';
+import { completionMiddleware } from '../../completionMiddleware';
+
+suite('Completion signature help', () => {
+    let sandbox: sinon.SinonSandbox;
+    let document: vscode.TextDocument;
+    let cancellation: vscode.CancellationTokenSource;
+    let configuration: sinon.SinonStub;
+    let enabled: sinon.SinonStub;
+    const position = new vscode.Position(0, 3);
+    const context = { triggerKind: vscode.CompletionTriggerKind.Invoke, triggerCharacter: undefined };
+    const provide = completionMiddleware.provideCompletionItem!;
+
+    function callItem(label = 'fun1', kind = vscode.CompletionItemKind.Function): vscode.CompletionItem {
+        const item = new vscode.CompletionItem(label, kind);
+        item.insertText = new vscode.SnippetString(`${label}($0)`);
+        return item;
+    }
+
+    setup(async () => {
+        document = await vscode.workspace.openTextDocument({ language: 'r', content: 'fun' });
+        cancellation = new vscode.CancellationTokenSource();
+        sandbox = sinon.createSandbox();
+        enabled = sandbox.stub().returns(true);
+        configuration = sandbox.stub(vscode.workspace, 'getConfiguration').callThrough();
+        configuration.withArgs('editor', document).returns({ get: enabled } as unknown as vscode.WorkspaceConfiguration);
+    });
+
+    teardown(() => {
+        sandbox.restore();
+        cancellation.dispose();
+    });
+
+    test('adds a command to function, package, method, and constructor call snippets', async () => {
+        const items = [callItem(), callItem('pkg::fun1'), callItem('`run task`', vscode.CompletionItemKind.Method),
+            callItem('new', vscode.CompletionItemKind.Constructor)];
+        const next = sandbox.stub().resolves(items);
+        const result = await provide(document, position, context, cancellation.token, next);
+
+        assert.strictEqual(result, items);
+        sinon.assert.calledOnceWithExactly(next, document, position, context, cancellation.token);
+        sinon.assert.calledWithExactly(configuration, 'editor', document);
+        sinon.assert.calledOnceWithExactly(enabled, 'parameterHints.enabled', true);
+        for (const item of items) {
+            assert.strictEqual(item.command?.command, 'editor.action.triggerParameterHints');
+        }
+    });
+
+    test('preserves completion-list metadata and uses the document setting on each request', async () => {
+        enabled.returns(false);
+        const item = callItem();
+        const list = new vscode.CompletionList([item], true);
+        const next = () => list;
+        assert.strictEqual(await provide(document, position, context, cancellation.token, next), list);
+        assert.strictEqual(item.command, undefined);
+        enabled.returns(true);
+        assert.strictEqual(await provide(document, position, context, cancellation.token, next), list);
+        assert.strictEqual(list.items[0].command?.command, 'editor.action.triggerParameterHints');
+        assert.strictEqual(list.isIncomplete, true);
+    });
+
+    test('leaves name-only completions, non-call snippets, fields, and existing commands alone', async () => {
+        const nameOnly = callItem();
+        nameOnly.insertText = 'fun1';
+        const plainText = callItem();
+        plainText.insertText = 'fun1($0)';
+        const snippetName = callItem();
+        snippetName.insertText = new vscode.SnippetString('fun1');
+        const afterCall = callItem();
+        afterCall.insertText = new vscode.SnippetString('fun1()$0');
+        const hasCommand = callItem();
+        const command = { title: 'Existing command', command: 'existing.command', arguments: ['original'] };
+        hasCommand.command = command;
+        const items = [nameOnly, plainText, snippetName, afterCall, callItem('field', vscode.CompletionItemKind.Field),
+            new vscode.CompletionItem('fun1', vscode.CompletionItemKind.Function)];
+
+        await provide(document, position, context, cancellation.token, () => [...items, hasCommand]);
+        assert.ok(items.every(item => item.command === undefined));
+        assert.strictEqual(hasCommand.command, command);
+    });
+
+    test('passes through empty and cancelled results', async () => {
+        for (const result of [undefined, null, [], new vscode.CompletionList()]) {
+            assert.strictEqual(await provide(document, position, context, cancellation.token, () => result), result);
+        }
+        const item = callItem();
+        const result = await provide(document, position, context, cancellation.token, () => {
+            cancellation.cancel();
+            return [item];
+        });
+        assert.deepStrictEqual(result, [item]);
+        assert.strictEqual(item.command, undefined);
+    });
+
+    test('handles LSP insert text, text edits, insert/replace edits, and completion-list defaults', async () => {
+        const client = new lsp.LanguageClient('completion-converter-test', 'Completion converter test',
+            { command: 'unused' }, { documentSelector: [] });
+        const range = lsp.Range.create(0, 0, 0, 3);
+        const base = { label: 'fun1', kind: lsp.CompletionItemKind.Function, insertTextFormat: lsp.InsertTextFormat.Snippet };
+        const responses: Array<lsp.CompletionItem[] | lsp.CompletionList> = [
+            [{ ...base, insertText: 'fun1($0)' }],
+            [{ ...base, insertText: 'ignored', textEdit: { range, newText: 'fun1($0)' } }],
+            [{ ...base, textEdit: { insert: range, replace: range, newText: 'fun1($0)' } }],
+            { isIncomplete: true, itemDefaults: { editRange: range, insertTextFormat: lsp.InsertTextFormat.Snippet },
+                items: [{ label: 'fun1', kind: lsp.CompletionItemKind.Function, textEditText: 'fun1($0)' }] }
+        ];
+        try {
+            for (const response of responses) {
+                const converted = await client.protocol2CodeConverter.asCompletionResult(response);
+                const result = await provide(document, position, context, cancellation.token, () => converted);
+                assert.ok(result);
+                const item = (Array.isArray(result) ? result : result.items)[0];
+                assert.strictEqual(item.command?.command, 'editor.action.triggerParameterHints');
+                // languageserver resolves documentation on the supplied item and
+                // returns it, including its command, through these converters.
+                const resolved = client.protocol2CodeConverter.asCompletionItem({
+                    ...client.code2ProtocolConverter.asCompletionItem(item), documentation: 'Function documentation'
+                });
+                assert.strictEqual(resolved.command?.command, 'editor.action.triggerParameterHints');
+                assert.strictEqual(resolved.documentation, 'Function documentation');
+            }
+        } finally {
+            await client.dispose();
+        }
+    });
+});
+
+suite('Completion signature help acceptance', () => {
+    const settings = () => vscode.workspace.getConfiguration('editor', { languageId: 'r' });
+    let previousHints: boolean | undefined;
+
+    async function until(predicate: () => boolean): Promise<void> {
+        const deadline = Date.now() + 5000;
+        while (!predicate()) {
+            assert.ok(Date.now() < deadline, 'Timed out waiting for completion or signature help');
+            await new Promise(resolve => setTimeout(resolve, 10));
+        }
+    }
+
+    suiteSetup(() => {
+        previousHints = settings().inspect<boolean>('parameterHints.enabled')?.globalLanguageValue;
+    });
+
+    suiteTeardown(async () => {
+        await settings().update('parameterHints.enabled', previousHints, vscode.ConfigurationTarget.Global, true);
+    });
+
+    for (const enabled of [true, false]) {
+        test(`accepting a resolved call snippet ${enabled ? 'requests' : 'does not request'} signature help when hints are ${enabled ? 'enabled' : 'disabled'}`, async () => {
+            await settings().update('parameterHints.enabled', enabled, vscode.ConfigurationTarget.Global, true);
+            const toServer = new PassThrough();
+            const toClient = new PassThrough();
+            const server = lsp.createProtocolConnection(toServer, toClient);
+            const signatures: lsp.SignatureHelpParams[] = [];
+            let resolutions = 0;
+            server.onRequest(lsp.InitializeRequest.type, (): lsp.InitializeResult => ({ capabilities: {
+                textDocumentSync: lsp.TextDocumentSyncKind.Full,
+                completionProvider: { resolveProvider: true },
+                signatureHelpProvider: { triggerCharacters: ['(', ','] }
+            } }));
+            server.onRequest(lsp.CompletionRequest.type, () => [{
+                label: 'fun1', kind: lsp.CompletionItemKind.Function,
+                insertTextFormat: lsp.InsertTextFormat.Snippet, insertText: 'fun1($0)'
+            }]);
+            server.onRequest(lsp.CompletionResolveRequest.type, item => {
+                resolutions++;
+                return { ...item, documentation: 'Adds 1 to its input.' };
+            });
+            server.onRequest(lsp.SignatureHelpRequest.type, params => {
+                signatures.push(params);
+                return { signatures: [{ label: 'fun1(x)', parameters: [{ label: 'x' }] }], activeSignature: 0, activeParameter: 0 };
+            });
+            server.onRequest(lsp.ShutdownRequest.type, () => undefined);
+            server.listen();
+            const client = new lsp.LanguageClient('completion-acceptance-test', 'Completion acceptance test',
+                () => Promise.resolve({ reader: toClient, writer: toServer }),
+                { documentSelector: [{ scheme: 'untitled', language: 'r' }], middleware: completionMiddleware });
+            try {
+                await client.start();
+                const document = await vscode.workspace.openTextDocument({ language: 'r', content: 'fun' });
+                const editor = await vscode.window.showTextDocument(document);
+                editor.selection = new vscode.Selection(0, 3, 0, 3);
+                await vscode.commands.executeCommand('editor.action.triggerSuggest');
+                await until(() => resolutions > 0);
+                assert.strictEqual(signatures.length, 0, 'Browsing completions must not request signature help');
+                await vscode.commands.executeCommand('acceptSelectedSuggestion');
+                await until(() => document.getText() === 'fun1()');
+                if (enabled) {
+                    await until(() => signatures.length > 0);
+                    assert.deepStrictEqual(signatures[0].position, { line: 0, character: 5 });
+                    assert.strictEqual(signatures[0].textDocument.uri, document.uri.toString());
+                } else {
+                    await new Promise(resolve => setTimeout(resolve, 100));
+                    assert.strictEqual(signatures.length, 0);
+                }
+                assert.strictEqual(editor.selection.active.character, 5);
+            } finally {
+                await vscode.commands.executeCommand('closeParameterHints');
+                await vscode.commands.executeCommand('hideSuggestWidget');
+                await vscode.commands.executeCommand('workbench.action.revertAndCloseActiveEditor');
+                await client.dispose();
+                server.dispose();
+                toServer.destroy();
+                toClient.destroy();
+            }
+        });
+    }
+});