Support both main and master as default branches

[xt0rted]

Recently GitHub announced they were going to be renaming their default branches to main and that this should become the default for new repos too. Other repos have already made the switch.

There's a few spots where the code assumes master as the default.

OctoLinker/packages/plugin-go/index.js

Lines 20 to 35 in 9e606a9

	if (!path.length) {
	return [
	`{BASE_URL}/${user}/${repo}/blob/master/${repo}.go`,
	`{BASE_URL}/${user}/${repo}`,
	];
	}
	const fullPath = path.join('/');
	const last = path.slice(-1);
	return [
	`{BASE_URL}/${user}/${repo}/blob/master/${fullPath}/${last}.go`,
	`{BASE_URL}/${user}/${repo}/tree/master/${fullPath}`,
	`{BASE_URL}/${user}/${repo}`,
	];
	}

OctoLinker/packages/plugin-homebrew-manifest/index.js

Lines 10 to 13 in 9e606a9

	return [
	relativeFile({ path, target }),
	`https://github.com/Homebrew/homebrew-core/blob/master/Formula/${target}`,
	];

The remaining spots all look to be related to tests.

The GitHub Actions plugin is already handling this but might need to be changed depending on how this is handled going forward.

OctoLinker/packages/plugin-github-actions/index.js

Lines 21 to 24 in 9e606a9

	return [
	`{BASE_URL}/${join(org, repo, 'tree', 'main', ...folder)}`,
	`{BASE_URL}/${join(org, repo, 'tree', 'master', ...folder)}`,
	];

[xt0rted]

We might not need to make any changes here. Recently GitHub made an update so links to branches that don't exist redirect to the default branch.

Revisiting the changes in #943, removing the main option from the returned urls and clicking on the link in the test file brings you to the correct url. I'm not sure how the tests will resolve & handle this though.

[jimeh]

The redirect from deleted to main branch thing doesn't solve things for new repos which never had a master branch, but instead was created with a main branch.

Also some repos use custom default branches, I'd suggest that OctoLinker should actually lookup what the default branch is for a repo, and use that.

[stefanbuck]

I agree that looking up what the actual default branch for a repo is would be the ideal solution. However, I'm less sure how to implement this given this requires an API call that needs to be resolved before anything else. Also, for users without a token it could eat up the rate limit quickly. I think we should do a best effort here given that either master or main the default branch in most repositories.

[jimeh]

Ah, true, requiring an API for that would be annoying. Maybe it could be somewhat cleaver and look it up if an API key is available, otherwise try master, and if that fails try main? And I assume default branch info could probably be cached rather safely.

[silverwind]

There is a trick to get the default branch without any guessing involved: Specify HEAD instead of the branch name. For example, this triggers a branch redirection message:

https://github.com/facebook/jest/tree/master/packages/jest-environment-jsdom

But this doesn't:

https://github.com/facebook/jest/tree/HEAD/packages/jest-environment-jsdom