Trim Co-authored-by trailers from default PR description (microsoft#8749)

* Initial plan

* Strip Co-authored-by trailers from default PR description

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/common/gitUtils.ts

@@ -7,6 +7,28 @@ import * as vscode from 'vscode';
 import { Repository } from '../api/api';
 import { GitApiImpl } from '../api/api1';
 
+/**
+ * Removes `Co-authored-by:` trailer lines from a commit message body.
+ *
+ * These lines are typically added at the bottom of a commit message (for example by
+ * the Copilot CLI or `git commit --trailer`) and are not useful when the commit body
+ * is reused as the default PR description.
+ */
+export function stripCoAuthoredByTrailers(body: string): string {
+	if (!body) {
+		return body;
+	}
+	const lines = body.split('\n');
+	const filtered = lines.filter(line => !/^\s*Co-authored-by:\s/i.test(line));
+	// Remove any trailing blank lines that may have been left behind once the
+	// trailer block is gone, but preserve internal blank lines / paragraph breaks.
+	let end = filtered.length;
+	while (end > 0 && filtered[end - 1].trim() === '') {
+		end--;
+	}
+	return filtered.slice(0, end).join('\n');
+}
+
 /**
  * Unwraps lines that were wrapped for conventional commit message formatting (typically at 72 characters).
  * Similar to GitHub's behavior when converting commit messages to PR descriptions.

src/github/folderRepositoryManager.ts

@@ -34,7 +34,7 @@ import { AuthProvider, GitHubServerType } from '../common/authentication';
 import { commands, contexts } from '../common/executeCommands';
 import { InMemFileChange, SlimFileChange } from '../common/file';
 import { findLocalRepoRemoteFromGitHubRef } from '../common/githubRef';
-import { unwrapCommitMessageBody } from '../common/gitUtils';
+import { stripCoAuthoredByTrailers, unwrapCommitMessageBody } from '../common/gitUtils';
 import { Disposable, disposeAll } from '../common/lifecycle';
 import Logger from '../common/logger';
 import { Protocol, ProtocolType } from '../common/protocol';
@@ -3213,7 +3213,7 @@ export const titleAndBodyFrom = async (promise: Promise<string | undefined>): Pr
 	}
 	const idxLineBreak = message.indexOf('\n');
 	const hasBody = idxLineBreak !== -1;
-	const rawBody = hasBody ? message.slice(idxLineBreak + 1).trim() : '';
+	const rawBody = hasBody ? stripCoAuthoredByTrailers(message.slice(idxLineBreak + 1)).trim() : '';
 	return {
 		title: hasBody ? message.slice(0, idxLineBreak) : message,
 

src/test/github/folderRepositoryManager.test.ts

@@ -342,4 +342,44 @@ describe('titleAndBodyFrom', function () {
 		assert.strictEqual(result?.title, 'This is a test');
 		assert.strictEqual(result?.body, '- A fslilenfilnf flen felslnf lsefl fnels  Leknef Lkdfnle  lfkenSlefn Lnkef LefnLienf LIfnels\n- B\n- C');
 	});
+
+	it('strips Co-authored-by trailer lines from body', async function () {
+		const message = Promise.resolve('title\n\nSome description.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>');
+
+		const result = await titleAndBodyFrom(message);
+		assert.strictEqual(result?.title, 'title');
+		assert.strictEqual(result?.body, 'Some description.');
+	});
+
+	it('strips multiple Co-authored-by trailer lines', async function () {
+		const message = Promise.resolve('title\n\nSome description.\n\nCo-authored-by: Alice <alice@example.com>\nCo-authored-by: Bob <bob@example.com>');
+
+		const result = await titleAndBodyFrom(message);
+		assert.strictEqual(result?.title, 'title');
+		assert.strictEqual(result?.body, 'Some description.');
+	});
+
+	it('strips Co-authored-by case-insensitively', async function () {
+		const message = Promise.resolve('title\n\nSome description.\n\nco-authored-by: Alice <alice@example.com>');
+
+		const result = await titleAndBodyFrom(message);
+		assert.strictEqual(result?.title, 'title');
+		assert.strictEqual(result?.body, 'Some description.');
+	});
+
+	it('preserves other trailers when stripping Co-authored-by', async function () {
+		const message = Promise.resolve('title\n\nSome description.\n\nSigned-off-by: Alice <alice@example.com>\nCo-authored-by: Bob <bob@example.com>');
+
+		const result = await titleAndBodyFrom(message);
+		assert.strictEqual(result?.title, 'title');
+		assert.strictEqual(result?.body, 'Some description.\n\nSigned-off-by: Alice <alice@example.com>');
+	});
+
+	it('returns empty body when only Co-authored-by trailers are present', async function () {
+		const message = Promise.resolve('title\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>');
+
+		const result = await titleAndBodyFrom(message);
+		assert.strictEqual(result?.title, 'title');
+		assert.strictEqual(result?.body, '');
+	});
 });