Existing repositories are no longer updated if Git tag is changed

[mliebischer]

I am coming from v2 and have recently started with v4. I have noticed that updating the Git tag within the branch option no longer update existing repositories correctly.

Steps to reproduce:

1. Create a simple configuration file with the branch option set to an existing Git tag, e.g. 8.0.0 for plone.restapi.

[plone.restapi]
url = https://github.com/plone/plone.restapi.git
branch = 8.0.0

3. Run mxdev -c mxdev.ini to fetch the package initially.
4. Change the branch option to 9.0.0.

[plone.restapi]
url = https://github.com/plone/plone.restapi.git
branch = 9.0.0

6. Run mxdev -c mxdev.ini again to update your existing repo.
7. Check the Git tag of the currently checked out repository. You can use git describe --tags for this.

Actual result:
You will see that the repository remains on the old tag 8.0.0.

Expected result:
The repository should be updated to 9.0.0.

Affected versions:

pip install mxdev==4.0.3 # broken
pip install mxdev==2.1.0 # works

I suspect this is related to the recent VCS code change, but I have not checked this further, see https://github.com/mxstack/mxdev/blob/main/CHANGES.md#300b1-2022-11-21

Side note:
Changing branch = main to branch = portlets works fine. It seems that only tag does not work anymore.

[jensens]

Root Cause Analysis

Location: src/mxdev/vcs/git.py - git_update() method (lines 234-280)

The Bug:

When updating an existing repository, Git tags (stored in the branch configuration) are incorrectly treated as if they were branches, which causes tag switching to fail.

How it Fails:

In git_update() at lines 249-251:

elif "branch" in self.source:
    stdout, stderr = self.git_switch_branch(stdout, stderr)
    stdout, stderr = self.git_merge_rbranch(stdout, stderr)

This code assumes the value in branch is an actual Git branch, so it:

1. Calls git_switch_branch() to switch to the branch
2. Calls git_merge_rbranch() to merge the remote branch

However, when branch = 9.0.0 (a tag), git_switch_branch() (lines 189-232) tries to find "9.0.0" in the output of git branch -a.

The problem: Tags don't appear in branch listings - they appear in git tag -l output instead.

Why Initial Checkout Works but Update Doesn't:

• Initial checkout: git clone -b 8.0.0 works because Git recognizes 8.0.0 as a tag and checks it out in detached HEAD state
• Update: The code tries to treat the tag as a branch:
  1. git fetch runs successfully (fetches all tags including the new one)
  2. git_switch_branch() looks for the tag name in the branch list
  3. Doesn't find it (tags ≠ branches)
  4. Either errors out or falls through without switching to the new tag

Expected Flow for Tags:

When the branch value is actually a tag, the update logic should:

1. Run git fetch to get all remote updates (including new tags)
2. Detect that the value is a tag, not a branch
3. Run git checkout <tag> directly (no merge needed - tags are immutable pointers)
4. Skip the git_merge_rbranch() call (you can't merge a tag)

Why This is a Regression:

The comment in the issue mentions this worked in v2.x but broke around v3.0.0b1. The VCS code was likely refactored during that time and the tag vs branch distinction was lost.

The Fix:

Need to add tag detection in git_update():

1. After git fetch, check if the branch value is actually a tag using git tag -l <name>
2. If it's a tag: git checkout <tag> directly
3. If it's a branch: use existing git_switch_branch() + git_merge_rbranch() logic