Switch from a detached head to a branch not working

[fcollonval]

If the repository is in detached head (for example after switching to a tag), then switching to a branch will fail.

Error message:

fatal: ambiguous argument '(HEAD detached at v0.20.0)': unknown revision or path not in the working tree. Use '--' to separate paths from revisions, like this: 'git <command> [<revision>...] -- [<file>...]' 

[Bl4ck-h00d]

Hi! I would like to work on this, can you help me how to get started?!

[fcollonval]

Hey @Bl4ck-h00d

Thanks for kicking in.

The extension has two parts: a front-end in Typescript and a back-end in Python. Whenever you trigger an action from the front-end, it will call a git command in the back-end.

In this case, to switch branch, the command call is done there:

jupyterlab-git/jupyterlab_git/git.py

Line 880 in 02c6d9a

async def checkout_branch(self, branchname, path):

The action is triggered in the frontend with that callback:

jupyterlab-git/src/components/BranchMenu.tsx

Line 402 in 02c6d9a

async function onClick(): Promise<void> {

The workflow is the following:

1. onClick is triggered with the branch name
2. it calls the model.checkout method

   jupyterlab-git/src/model.ts

   Line 426 in 02c6d9a

   async checkout(options?: Git.ICheckoutOptions): Promise<Git.ICheckoutResult> {

The model is handling the repository state and the call to the backend

3. That trigger a call to the backend

   jupyterlab-git/src/model.ts

   Line 469 in 02c6d9a

   const d = await requestAPI<Git.ICheckoutResult>(

4. The call is catch by a Python handler:

   jupyterlab-git/jupyterlab_git/handlers.py

   Line 443 in 02c6d9a

   async def post(self, path: str = ""):

5. That handler calls the git command mentioned above:

   jupyterlab-git/jupyterlab_git/handlers.py

   Line 456 in 02c6d9a

   body = await self.git.checkout_branch(data["branchname"], local_path)

The troubles is in the front-end because we want to deal with files that are different between two branches at

jupyterlab-git/src/model.ts

Line 458 in 02c6d9a

changes = await this._changedFiles(

This calls:

with

{"base":"(HEAD detached at v0.21.0)","remote":"master"}

base is not a valid ref; hence the error seen.

I'll update the description with an animation.

Let me know if you need more information and don't hesitate to open a PR early to discuss your fix.

[fcollonval]

Transforming the fake branch name (HEAD detached at #####) to ##### before calling model.checkout should solve this issue.

Transforming the fake branch name (HEAD detached at #####) to ##### before calling this._changedFiles at:

jupyterlab-git/src/model.ts

Line 459 in 02c6d9a

this._currentBranch.name,

should solve this issue.

[fcollonval]

Fixed by #1218