Create PR shows error if there has been a previous PR on that branch (#7270)

Fixes #7018

Author: alexr00

src/github/createPRViewProvider.ts

@@ -618,8 +618,13 @@ export class CreatePullRequestViewProvider extends BaseCreatePullRequestViewProv
 	}
 
 	private async existingPRMessage(): Promise<string | undefined> {
-		const existingPR = await PullRequestGitHelper.getMatchingPullRequestMetadataForBranch(this._folderRepositoryManager.repository, this.model.compareBranch);
-		return existingPR ? vscode.l10n.t('A pull request already exists for this branch.') : '';
+		const [existingPR, hasUpstream] = await Promise.all([PullRequestGitHelper.getMatchingPullRequestMetadataForBranch(this._folderRepositoryManager.repository, this.model.compareBranch), this.model.getCompareHasUpstream()]);
+		if (!existingPR || !hasUpstream) {
+			return undefined;
+		}
+
+		const [pr, compareBranch] = await Promise.all([await this._folderRepositoryManager.resolvePullRequest(existingPR.owner, existingPR.repositoryName, existingPR.prNumber), this._folderRepositoryManager.repository.getBranch(this.model.compareBranch)]);
+		return (pr?.head?.sha === compareBranch.commit) ? vscode.l10n.t('A pull request already exists for this branch.') : undefined;
 	}
 
 	public async setDefaultCompareBranch(compareBranch: Branch | undefined) {

src/github/githubRepository.ts

@@ -1114,7 +1114,7 @@ export class GitHubRepository extends Disposable {
 		return buff;
 	}
 
-	async hasBranch(branchName: string): Promise<boolean> {
+	async hasBranch(branchName: string): Promise<string | undefined> {
 		Logger.appendLine(`Fetch branch ${branchName} - enter`, this.id);
 		const { query, remote, schema } = await this.ensure();
 
@@ -1127,7 +1127,7 @@ export class GitHubRepository extends Disposable {
 			}
 		});
 		Logger.appendLine(`Fetch branch ${branchName} - done: ${data.repository?.ref !== null}`, this.id);
-		return data.repository?.ref !== null;
+		return data.repository?.ref?.target.oid;
 	}
 
 	async listBranches(owner: string, repositoryName: string): Promise<string[]> {

src/github/graphql.ts

@@ -576,7 +576,7 @@ export interface GetBranchResponse {
 			target: {
 				oid: string;
 			}
-		}
+		} | null;
 	} | null;
 }
 

src/view/createPullRequestDataModel.ts

@@ -155,6 +155,11 @@ export class CreatePullRequestDataModel extends Disposable {
 	private async updateHasUpstream(branch: string): Promise<boolean> {
 		const compareBranch = await this.folderRepositoryManager.repository.getBranch(branch);
 		this._compareHasUpstream = !!compareBranch.upstream;
+		// Check that the upstream head matches the local head
+		if (this._compareHasUpstream) {
+			const upstream = await this.gitHubRepository?.hasBranch(branch);
+			this._compareHasUpstream = upstream === compareBranch.commit;
+		}
 		return this._compareHasUpstream;
 	}