Reliability fixes for `default-branch-button` (#6629)

1 files changed, 32 insertions, 0 deletions

diff --git a/source/github-helpers/get-current-git-ref.ts b/source/github-helpers/get-current-git-ref.ts
new file mode 100644
index 00000000..4eefbabb
--- /dev/null
+++ b/source/github-helpers/get-current-git-ref.ts
@@ -0,0 +1,32 @@
+import {getCurrentBranchFromFeed} from './index.js';
+
+const typesWithGitRef = new Set(['tree', 'blob', 'blame', 'edit', 'commit', 'commits', 'compare']);
+const titleWithGitRef = / at (?<branch>[.\w-/]+)( · [\w-]+\/[\w-]+)?$/i;
+
+/** This only works with URL and page title. Must not be async because it's used by GitHubURL */
+export default function getCurrentGitRef(pathname = location.pathname, title = document.title): string | undefined {
+	if (!pathname.startsWith('/')) {
+		throw new TypeError(`Expected pathname starting with /, got "${pathname}"`);
+	}
+
+	const [type, gitRefIfNonSlashed] = pathname.split('/').slice(3);
+	if (!type || !typesWithGitRef.has(type)) {
+		// Root; or piece of information not applicable to the page
+		return;
+	}
+
+	// Slashed branches on `commits`
+	if (type === 'commits') {
+		return getCurrentBranchFromFeed()!;
+	}
+
+	// Slashed branches on `blob` and `tree`
+	const parsedTitle = titleWithGitRef.exec(title);
+	if (parsedTitle) {
+		return parsedTitle.groups!.branch;
+	}
+
+	// Couldn't ensure it's not slashed, so we'll return the first piece whether correct or not
+	// TODO: extract from `ref-selector` if available https://github.com/refined-github/refined-github/issues/6557
+	return gitRefIfNonSlashed;
+}