ENH: Add update-third-party Agent Skill for VS Code Copilot

.github/skills/update-third-party/SKILL.md

@@ -0,0 +1,142 @@
+---
+name: update-third-party
+description: 'Update an ITK third-party library to a new version. Use when: bumping a vendored dependency version, updating ThirdParty module, running UpdateFromUpstream.sh. Creates a new branch with the tag-update commit and runs the extraction script.'
+argument-hint: 'Which third-party library to update and the new version/tag'
+---
+
+# Update ITK Third-Party Library
+
+Creates a new git branch with the commits needed to update a vendored third-party library in `Modules/ThirdParty/`.
+
+## When to Use
+
+- Updating a third-party library (e.g., JPEG, ZLIB, HDF5, GoogleTest) to a new upstream version
+- User says "update <library> to <version>"
+
+## Inputs
+
+Gather these from the user before starting:
+
+| Input | Example | Required |
+|-------|---------|----------|
+| Library name | `JPEG`, `ZLIB`, `GoogleTest` | Yes |
+| New version/tag | `3.1.0`, `v1.18.0`, commit hash | Yes |
+| Branch name | `update_jpeg` | No (auto-generated) |
+
+## Procedure
+
+### 1. Locate the Update Script
+
+Find the module's update script in `Modules/ThirdParty/<NAME>/`. The script name varies:
+- Most modules: `UpdateFromUpstream.sh`
+- DoubleConversion: `UpdateDoubleConversionFromGoogle.sh`
+
+If there is no update script it is an error! STOP.
+
+Read the script to understand the module's configuration (`name`, `tag`, `repo`, `paths`, `extract_source` function).
+
+### 2. Create a New Branch
+
+```bash
+git fetch origin
+git checkout -b update_<lowercase_name> origin/main
+```
+
+Replace `<lowercase_name>` with a short snake_case identifier (e.g., `update_jpeg`, `update_zlib`, `update_hdf5`). If the user specifies a branch name, use that instead.
+
+### 3. Update the Tag in the Update Script
+
+Edit the `readonly tag="..."` line in the update script to the new version. Only change the `tag` value — nothing else.
+
+Commit this change:
+
+```bash
+git add Modules/ThirdParty/<NAME>/<UpdateScript>.sh
+git commit -m "ENH: Update <library-name> to <version>"
+```
+
+The commit message body may optionally include links to upstream release notes or changelog.
+
+### 4. Run the Update Script
+
+```bash
+./Modules/ThirdParty/<NAME>/<UpdateScript>.sh
+```
+
+This script (powered by `Utilities/Maintenance/update-third-party.bash`):
+1. Clones the upstream repository
+2. Checks out the specified tag
+3. Runs `extract_source()` to prepare a clean subtree
+4. Finds the previous import commit via git history
+5. Merges the upstream changes into `Modules/ThirdParty/<NAME>/src/`
+6. Creates a merge commit.
+
+
+### 5. Resolve Any Merge Conflicts
+
+If there are merge conflicts during the extraction step, the script will pause and prompt you to resolve them in the `work/` directory.
+
+Inspect the git history for local changes, and determine ITK's local changes, and the upstream changes. Use your judgment to resolve the conflicts, then stage and commit the resolved files.
+
+```bash
+git add <resolved-files>
+git commit
+```
+
+
+### 6. Handle Post-Update Steps (if needed)
+
+Some modules require additional work after extraction:
+
+- **Mangling**: If the module uses symbol mangling, you may need to regenerate the mangled headers. This is common for C libraries like JPEG and ZLIB. Follow the instructions in the module's `src/` directory (e.g., `src/itkjpeg/src/itk_jpeg_mangle.h.in`).
+- **Build fixes**: If the upstream CMake changed significantly, the module's outer `CMakeLists.txt` may need updates. Commit these as separate `COMP:` or `ENH:` commits.
+
+
+### 7. Verify the Result
+
+Verify the commit history:
+
+```bash
+git log --oneline -3
+git diff HEAD~2..HEAD --stat
+```
+
+### 8. Build and Test the changes locally
+
+Build ITK with the updated module to ensure there are no build errors.
+### 9. Push and Create PR
+
+The branch is ready for pushing and PR creation. The PR should target `main`.
+
+Determine which remote is the user's fork:
+
+```bash
+git remote -v
+```
+
+Push the branch to the user's fork:
+
+```bash
+git push <remote-name> update_<lowercase_name>
+```
+
+Use the GitHub MCP to create a PR for `main` with a title like "ENH: Update <library> to <version>". The PR description should include:
+- A summary of the update
+- Links to upstream release notes or changelog
+- Any relevant notes about the update (e.g., if there were significant merge conflicts or build
+fixes needed)
+- That the commit was generated by the `update-third-party` skill
+
+
+
+## Troubleshooting
+
+| Problem | Solution |
+|---------|----------|
+| `No previous import commit found` | The module may use `exact_tree_match=false`; check the script |
+| Merge conflicts during extraction | Resolve conflicts under the ThridParty directory
+## Reference
+
+- Official documentation: [Updating Third Party Projects](../../../Documentation/docs/contributing/updating_third_party.md)
+- Master update script: [Utilities/Maintenance/update-third-party.bash](../../../Utilities/Maintenance/update-third-party.bash)
+- All third-party modules: [Modules/ThirdParty/](../../../Modules/ThirdParty/)

Documentation/docs/contributing/updating_third_party.md

@@ -45,6 +45,43 @@ git checkout -b update_doubleconversion
 
 Now you can review the change and make a merge request from the branch as normal.
 
+Using the Automated Skill (VS Code with GitHub Copilot)
+--------------------------------------------------------
+
+For VS Code users with GitHub Copilot, an automated [update-third-party skill]
+streamlines the update process. The skill automates the workflow described above:
+creating a branch, updating the tag, running the extraction script, resolving
+conflicts, and creating a pull request. To create a pull request, the GitHub MCP is recommended.
+
+To use the skill, invoke it via Copilot by providing the library name and
+version tag:
+
+```
+@workspace /update-third-party <library-name> <version-tag>
+```
+
+For example:
+
+```
+@workspace /update-third-party PNG v1.6.54
+```
+
+See the skill for details of the steps.
+
+The steps may involve resolving conflicts and updating name mangling. These steps should be carefully reviewed and verified.
+
+This is particularly useful for routine updates where the upstream changes are
+straightforward. The skill follows ITK's conventions for commit messages,
+branch naming, and PR descriptions.
+
+**When to use the skill:**
+- Updating to a new tagged release of an existing third-party library
+- The library already has a working `UpdateFromUpstream.sh` script
+- You want to automate the mechanical aspects of the update process
+
+
+See the [update-third-party skill] documentation for complete details.
+
 Porting a Project
 -----------------
 
@@ -117,3 +154,4 @@ if necessary.
 
 
 [update-third-party.bash]: https://github.com/InsightSoftwareConsortium/ITK/blob/main/Utilities/Maintenance/update-third-party.bash
+[update-third-party skill]: https://github.com/InsightSoftwareConsortium/ITK/blob/main/.github/skills/update-third-party/SKILL.md