Sync fork prior to creating reference and handle NotFoundException

[ryfu-msft]

Fixes #287

A NotFoundException occurs when the forked repo is behind by too many commits. This fails even when attempting to sync the forked repo with the upstream which nullifies my previous fix #235

To address this issue, I have added the following changes:

1. Always attempt to sync fork but make it nonblocking if it fails as creating a reference could still possibly succeed. (Example: unable to sync fork because it is a fast-forward update)
2. Add a friendly error message if a NotFoundException is encountered instructing the user to manually sync their fork.

Current tests should verify that submission succeeds as this is a minor edge case that is difficult to replicate due to the requirement of the fork needing to be behind by X amount of commits.

Microsoft Reviewers: Open in CodeFlow

[Trenly]

I'm not sure how winget-create handles the forks and branches, but given that we have the upstream information in order to update the fork, couldn't the commit be applied directly to a detached head which is the latest commit to the default branch of upstream, removing the need to check if the fork is behind at all?

[ryfu-msft]

I'm not sure how winget-create handles the forks and branches, but given that we have the upstream information in order to update the fork, couldn't the commit be applied directly to a detached head which is the latest commit to the default branch of upstream, removing the need to check if the fork is behind at all?

Linking to the source code in case you were curious how it was implemented:

winget-create/src/WingetCreateCore/Common/GitHub.cs

Lines 278 to 378 in 49a1fb4

	private async Task<PullRequest> SubmitPRAsync(string packageId, string version, Dictionary<string, string> contents, bool submitToFork)
	{
	bool createdRepo = false;
	Repository repo;
	if (submitToFork)
	{
	try
	{
	var user = await this.github.User.Current();
	repo = await this.github.Repository.Get(user.Login, this.wingetRepo);
	}
	catch (NotFoundException)
	{
	repo = await this.github.Repository.Forks.Create(this.wingetRepoOwner, this.wingetRepo, new NewRepositoryFork());
	createdRepo = true;
	}
	}
	else
	{
	repo = await this.github.Repository.Get(this.wingetRepoOwner, this.wingetRepo);
	}
	string newBranchName = $"autogenerated/{packageId}/{Guid.NewGuid()}";
	string newBranchNameHeads = $"heads/{newBranchName}";
	string message = $"{packageId} version {version}";
	var upstreamMaster = await this.github.Git.Reference.Get(this.wingetRepoOwner, this.wingetRepo, HeadMasterRef);
	var upstreamMasterSha = upstreamMaster.Object.Sha;
	Reference newBranch = null;
	try
	{
	var retryPolicy = Policy.Handle<ApiException>().WaitAndRetryAsync(3, i => TimeSpan.FromSeconds(i));
	await retryPolicy.ExecuteAsync(async () =>
	{
	try
	{
	await this.github.Git.Reference.Create(repo.Id, new NewReference($"refs/{newBranchNameHeads}", upstreamMasterSha));
	}
	catch (Octokit.NotFoundException)
	{
	// Creating a reference can sometimes fail with a NotFoundException if the fork is not up to date with the upstream repository.
	await this.UpdateForkedRepoWithUpstreamCommits(repo);
	throw;
	}
	});
	// Update from upstream branch master
	newBranch = await this.github.Git.Reference.Update(repo.Id, newBranchNameHeads, new ReferenceUpdate(upstreamMasterSha));
	var updatedSha = newBranch.Object.Sha;
	var nt = new NewTree { BaseTree = updatedSha };
	string appPath = Utils.GetAppManifestDirPath(packageId, version, '/');
	foreach (KeyValuePair<string, string> item in contents)
	{
	string file = $"{appPath}/{item.Key}.yaml";
	nt.Tree.Add(new NewTreeItem { Path = file, Mode = "100644", Type = TreeType.Blob, Content = item.Value });
	}
	var newTree = await this.github.Git.Tree.Create(repo.Id, nt);
	var newCommit = new NewCommit(message, newTree.Sha, updatedSha);
	var commit = await this.github.Git.Commit.Create(repo.Id, newCommit);
	await this.github.Git.Reference.Update(repo.Id, newBranchNameHeads, new ReferenceUpdate(commit.Sha));
	// Get latest description template from repo
	string description = await this.GetFileContentsAsync(PRDescriptionRepoPath);
	string targetBranch = submitToFork ? repo.Parent.DefaultBranch : repo.DefaultBranch;
	var newPullRequest = new NewPullRequest(message, $"{repo.Owner.Login}:{newBranchName}", targetBranch) { Body = description };
	var pullRequest = await this.github.PullRequest.Create(this.wingetRepoOwner, this.wingetRepo, newPullRequest);
	return pullRequest;
	}
	catch (Exception)
	{
	// On error, cleanup created branch/repo before re-throwing
	if (createdRepo)
	{
	try
	{
	await this.github.Repository.Delete(repo.Id);
	}
	catch (ForbiddenException)
	{
	// If we fail to delete the fork, the user did not provide a token with the "delete_repo" permission. Do nothing.
	}
	}
	else if (newBranch != null)
	{
	await this.github.Git.Reference.Delete(repo.Id, newBranch.Ref);
	}
	throw;
	}
	}

We already assign the new reference with the latest SHA1 value directly from the upstream default branch before attempting to create it. Even though we don't interact with the forked repo except when creating the new branch/reference, it seems like an outdated fork unintentionally impacts the Reference.Create() function and causes it to fail.