A Short Exploration of Github URLs

Github urls look like:

https://github.com/$user/$repo/blob/$commit/$path

A fun & interesting fact is that $commit can contain slashes.

So how do you deal with the possible ambiguities? First, it looks like git does not allow you to have commit IDs (like branches or tags) that are both root and leaf paths:

~/src/github-url-parsing$ git checkout -b release
Switched to a new branch 'release'
~/src/github-url-parsing$ git checkout -b release/README
error: unable to resolve reference refs/heads/release/README: Not a directory
fatal: Failed to lock ref for update: Not a directory

~/src/github-url-parsing$ git checkout -b test/1.5 
Switched to a new branch 'test/1.5'
~/src/github-url-parsing$ git checkout -b test
error: there are still refs under 'refs/heads/test'
fatal: Failed to lock ref for update: Is a directory

which means you can’t have both release/README (branch + path) and release/README (branch). The same holds true for tags:

~/src/github-url-parsing$ git tag foo
~/src/github-url-parsing$ git tag foo/bar
error: unable to resolve reference refs/tags/foo/bar: Not a directory
fatal: refs/tags/foo/bar: cannot lock the ref
~/src/github-url-parsing$ git tag bar/baz
~/src/github-url-parsing$ git tag bar
error: there are still refs under 'refs/tags/bar'
fatal: refs/tags/bar: cannot lock the ref

this appears to be reliably enforced by github, even though they use a non-standard git implementation:

~/src/gup2$ git tag root/branch
~/src/gup2$ git push origin root/branch
Total 0 (delta 0), reused 0 (delta 0)
To [email protected]:krakensden/github-url-parsing.git
 * [new tag]         root/branch -> root/branch

~/src/github-url-parsing$ git tag root
~/src/github-url-parsing$ git push origin root
Total 0 (delta 0), reused 0 (delta 0)
To [email protected]:krakensden/github-url-parsing.git
 ! [remote rejected] root -> root (cannot lock ref 'refs/tags/root': 'refs/tags/root/branch' exists; cannot create 'refs/tags/root')
 error: failed to push some refs to '[email protected]:krakensden/github-url-parsing.git'