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).
• Added an explicit test skip due to failure of detection of svn in windows-2025.

Description of how this change was tested

1. Testing against vcs2l old pull requests

• First, clone the codebase:

  git clone [email protected]: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 [email protected]: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 26.86%. Comparing base (3d0f2f9) to head (e4d26d4).

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

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
- Coverage   26.98%   26.86%   -0.13%     
==========================================
  Files          31       31              
  Lines        2238     2248      +10     
  Branches      392      396       +4     
==========================================
  Hits          604      604              
- Misses       1574     1584      +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