Fix resolve conflicts button in focus view (#6024)

Fixes #5942

Author: alexr00

src/github/activityBarViewProvider.ts

@@ -11,7 +11,7 @@ import { dispose, formatError } from '../common/utils';
 import { getNonce, IRequestMessage, WebviewViewBase } from '../common/webview';
 import { ReviewManager } from '../view/reviewManager';
 import { FolderRepositoryManager } from './folderRepositoryManager';
-import { GithubItemStateEnum, IAccount, isTeam, reviewerId, ReviewEvent, ReviewState } from './interface';
+import { GithubItemStateEnum, IAccount, isTeam, PullRequestMergeability, reviewerId, ReviewEvent, ReviewState } from './interface';
 import { PullRequestModel } from './pullRequestModel';
 import { getDefaultMergeMethod } from './pullRequestOverview';
 import { PullRequestView } from './pullRequestOverviewCommon';
@@ -75,6 +75,32 @@ export class PullRequestViewProvider extends WebviewViewBase implements vscode.W
 		this.updatePullRequest(this._item);
 	}
 
+	private async updateBranch(message: IRequestMessage<string>): Promise<void> {
+		if (this._folderRepositoryManager.repository.state.workingTreeChanges.length > 0 || this._folderRepositoryManager.repository.state.indexChanges.length > 0) {
+			await vscode.window.showErrorMessage(vscode.l10n.t('The pull request branch cannot be updated when the there changed files in the working tree or index. Stash or commit all change and then try again.'), { modal: true });
+			return this._replyMessage(message, {});
+		}
+		const mergeSucceeded = await this._folderRepositoryManager.tryMergeBaseIntoHead(this._item, true);
+		if (!mergeSucceeded) {
+			this._replyMessage(message, {});
+		}
+		// The mergability of the PR doesn't update immediately. Poll.
+		let mergability = PullRequestMergeability.Unknown;
+		let attemptsRemaining = 5;
+		do {
+			mergability = (await this._item.getMergeability()).mergeability;
+			attemptsRemaining--;
+			await new Promise(c => setTimeout(c, 1000));
+		} while (attemptsRemaining > 0 && mergability === PullRequestMergeability.Unknown);
+
+		const result: Partial<PullRequest> = {
+			events: await this._item.getTimelineEvents(),
+			mergeable: mergability,
+		};
+		await this.refresh();
+		this._replyMessage(message, result);
+	}
+
 	protected async _onDidReceiveMessage(message: IRequestMessage<any>) {
 		const result = await super._onDidReceiveMessage(message);
 		if (result !== this.MESSAGE_UNHANDLED) {
@@ -107,6 +133,8 @@ export class PullRequestViewProvider extends WebviewViewBase implements vscode.W
 				return openPullRequestOnGitHub(this._item, (this._item as any)._telemetry);
 			case 'pr.checkout-default-branch':
 				return this.checkoutDefaultBranch(message);
+			case 'pr.update-branch':
+				return this.updateBranch(message);
 			case 'pr.re-request-review':
 				return this.reRequestReview(message);
 		}