多依赖项目从SVN迁移至Git（单仓库）的svn2git实施咨询

Great choice going with a monorepo for your inter-dependent projects—it’ll make cross-project changes way smoother. Let’s break down exactly how to pull this off with svn2git, keeping every project’s full commit history intact.

Prerequisites First #

Make sure you have these tools installed locally:

• Git
• Subversion command-line client (svn)
• svn2git (install via your package manager, e.g., brew install svn2git on macOS, or build from source if needed)
• A text editor to create an author mapping file (critical for preserving commit author info)

Step 1: Create an Author Mapping File #

SVN uses plain usernames, while Git expects the Name <email> format. Collect all unique usernames from all your SVN repos, then create a file (e.g., authors.txt) with entries like:

svn_user1 = Jane Doe <jane.doe@company.com>
svn_user2 = John Smith <john.smith@company.com>

Place this file somewhere accessible (e.g., the parent directory of your new Git repo).

Step 2: Initialize Your Unified Git Repo #

Start with a clean local Git repo to hold all your projects:

mkdir unified-monorepo
cd unified-monorepo
git init

Step 3: Migrate Each SVN Project to a Subdirectory (With Full History) #

For each SVN project, we’ll import its entire history into a dedicated subdirectory in the Git repo. The key here is using --prefix to scope the project to its subfolder, and handling branches/tags to avoid conflicts.

Option A: Migrate to a Branch (Recommended for Control)

This method keeps each project’s migration isolated, making it easier to resolve conflicts if they arise:

1. Create a temporary branch for the project:

   git checkout -b migrate-proj1
   

2. Migrate the SVN project to this branch, scoping it to proj1/ (adjust the SVN URL and prefix to match your project):

   • If your SVN repo uses the standard trunk/branches/tags layout:

     svn2git https://your-svn-server/svn/proj1 \
       --prefix=proj1/ \
       --branch-prefix=proj1/ \
       --tag-prefix=proj1/ \
       --authors ../authors.txt
     

   • If your SVN repo doesn’t use the standard layout (e.g., code lives directly at the root):

     svn2git https://your-svn-server/svn/proj1 \
       --trunk . \
       --prefix=proj1/ \
       --branch-prefix=proj1/ \
       --tag-prefix=proj1/ \
       --authors ../authors.txt
     

   The --branch-prefix and --tag-prefix ensure project-specific branches/tags don’t clash with others (e.g., proj1/feature-login instead of just feature-login).

3. Switch back to your main branch and merge the migrated project (use --allow-unrelated-histories since the SVN history is independent of Git’s initial state):

   git checkout main
   git merge migrate-proj1 --allow-unrelated-histories
   

4. Delete the temporary branch (optional but clean):

   git branch -d migrate-proj1
   

Repeat this process for every SVN project, adjusting the prefix and SVN URL each time.

Option B: Migrate Directly to Main Branch

If you’re confident no conflicts will occur (e.g., all projects have unique root files), you can migrate directly to the main branch for each project:

svn2git https://your-svn-server/svn/proj2 \
  --prefix=proj2/ \
  --branch-prefix=proj2/ \
  --tag-prefix=proj2/ \
  --authors ../authors.txt \
  --no-rebase

The --no-rebase flag prevents svn2git from trying to rebase onto existing commits, which would cause issues with unrelated histories.

Step 4: Validate the Migration #

Before pushing to a remote repo, verify everything is intact:

• Check the file structure: ls -la should show all your projects as subdirectories.
• Verify project history: Use git log --oneline -- proj1/ to see all commits specific to proj1—they should match your SVN history.
• Check tags/branches: Run git tag and git branch -a to ensure project-specific tags/branches were imported correctly.

Step 5: Push to Remote Git Repo #

Once you’re satisfied with the local migration, push everything to your remote Git host:

# Add the remote repo
git remote add origin git@your-git-server:your-team/unified-monorepo.git

# Push the main branch
git push -u origin main

# Push all tags
git push --tags

# Push project-specific branches (if you have any)
git push origin proj1/feature-new-ui
git push origin proj2/bugfix-payment

Key Tips to Avoid Headaches #

• Test first: Do a full dry run migration locally before touching any production repos.
• Resolve conflicts early: If two projects have overlapping files (e.g., root-level README.md), merge conflicts will pop up—resolve them manually and commit the fix.
• Keep SVN around temporarily: Don’t delete your SVN repos immediately. Wait a few weeks to ensure the Git repo is fully adopted and no critical history was missed.
• Update dependencies: Since your projects are now in a monorepo, update any internal dependency paths to use relative paths (e.g., ../proj2/lib instead of the old SVN URL).

内容的提问来源于stack exchange，提问作者Nikhil Khurana