Enable commit-specific git fetch for compatibility with external forks.

[leander-dsouza]

Basic Info

Info	Please fill out this column
Ticket(s) this addresses	resolves #8
Primary OS tested on	Ubuntu
Is this a breaking change?	No
Does this PR contain AI generated software?	No

---

Description of contribution in a few bullet points

• Enabled commit-specific fetching of origin on non-shallow clones containing hashes.
• This allows us to clone PRs from repositories not tied to the source branch for history (external forks).

Description of how this change was tested

1. Testing against vcs2l old pull requests

• First, clone the codebase:

  git clone git@github.com:ros-infrastructure/vcs2l.git vcs2l-ext-fork

• Next, use the following repos.yaml to get the commit hash of the following external fork:

  ---
  repositories:
    vcs2l-ext-fork:
      type: git
      url: 'https://github.com/ros-infrastructure/vcs2l.git'
      version: '4ad2dd14b0033c275e5faff7935c4a7d7581fee4'

• Finally, update the existing repository:

  vcs import --input repos.yaml

  This will successfully checkout the repository to the specific hash.
  This step fails without this contribution with the following error message:

  === ./vcs2l-ext-fork (git) ===
  Could not checkout ref '4ad2dd14b0033c275e5faff7935c4a7d7581fee4': fatal: reference is not a tree:    4ad2dd14b0033c275e5faff7935c4a7d7581fee4

2. Test against the reproduction step in the parent issue - dirk-thomas/vcstool#258

• Reproduction measures specified by @timor-raiman

  git clone git@github.com:timor-raiman/action-ros-ci.git -b vcs-issue && cd action-ros-ci
  git fetch origin +refs/pull/3/*:refs/remotes/origin/pr/3/*
  export PRMERGE_SHA=`git rev-parse origin/pr/3/merge`
  rm -rf new-path/ && mkdir -p new-path/
  cat test-vcs-issue.repo | envsubst | vcs import --force --recursive new-path/

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 26.84%. Comparing base (af4acfd) to head (9d6d6bc).

Files with missing lines	Patch %	Lines
vcs2l/clients/git.py	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
- Coverage   26.96%   26.84%   -0.12%     
==========================================
  Files          31       31              
  Lines        2240     2250      +10     
  Branches      393      397       +4     
==========================================
  Hits          604      604              
- Misses       1576     1586      +10     
  Partials       60       60              

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[Copilot]

Pull Request Overview

This pull request adds support for fetching specific commit hashes in non-shallow Git import mode, and improves test skipping for VCS tools that may not be installed.

• Refactored version type determination to work for both shallow and non-shallow modes
• Added explicit fetch of commit hashes for non-shallow repository imports
• Added test skipping when SVN or Mercurial tools are not available

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
vcs2l/clients/git.py	Refactored to determine version type earlier and fetch specific commit hashes in non-shallow mode for both existing and new repositories
test/test_commands.py	Added utility variables and skip decorator for tests requiring SVN and Mercurial
test/reimport_force.txt	Updated expected output to include fetch messages for commit hash imports
test/import.txt	Updated expected output to include fetch messages for commit hash imports

[cottsay]

The checks added here are part of the fixture setup in __init__.py. What's the motivation to duplicate them here?

[leander-dsouza]

They were initially duplicated as Subversion, and Mercurial ignores were flaky in Windows 2025 in previous workflow runs.

However, they currently work as expected, so I have dropped the additional commit.