## Summary Switch the 12-factor app extensions (Flask, Django, FastAPI, Go, Spring Boot, and the shared `_AppBase`) from the `charm` plugin to the `uv` plugin for building Python charms. ## What changed **`charmcraft/extensions/app.py`** - `_AppBase._get_charm_part()` — replaces `plugin: charm` with `plugin: uv` and swaps `build-snaps: [rustup]` + the `override-build` rustup-init script for `build-snaps: [astral-uv, rustup]`. The `astral-uv` snap provides the `uv` tool that the `uv` plugin expects; `rustup` remains to satisfy pydantic compilation. - `_AppBase.get_supported_bases()` — now returns both `ubuntu@22.04` and `ubuntu@24.04`. Previously only 22.04 was listed, but the `charmcraft init` templates generate `base: ubuntu@24.04`. This caused CI to reject the extension with "does not support base(s): ubuntu@24.04" after PR #2713 made base validation strict. - `SpringBootFramework.is_experimental()` — adds an explicit `is_experimental` override that returns `False`, making it clear this extension is production-ready and consistent with the other frameworks. **`tests/extensions/test_app.py`** Updated all expected `charm` part fixtures to match the new `uv` plugin shape (no `override-build`, both snaps listed). ## Why The `uv` plugin is the recommended way to install Python dependencies in modern charms. It: - Reads `pyproject.toml` or `requirements.txt` and installs deps via `uv sync` / `uv pip install` - Is faster and more reproducible than pip-based installs done in `override-build` - Avoids the bespoke `rustup default stable && craftctl default` override-build script The `charm` plugin is a legacy build path. Switching to `uv` aligns 12-factor charms with the current recommended charm development workflow. ## Testing - Unit tests: `make test` (all 2539 pass) - Snap tests: covered by CI via `charmcraft init --profile django-framework` + `charmcraft fetch-libs` on Ubuntu 20.04 and 22.04 spread nodes ## Related - Depends on PR #2713 (`feat(extensions): make extensions work with base`) which is now merged to main. - Trivy security scan failure (Django 5.1.4 in `docs/tutorial/code/django/requirements.txt`) is pre-existing and unrelated to this change. --- - [x] I've followed the [contribution guidelines](https://github.com/canonical/charmcraft/blob/main/CONTRIBUTING.md). - [x] I've signed the [CLA](http://www.ubuntu.com/legal/contributors/). - [x] I've successfully run `make lint && make test`. - [x] I've added or updated any relevant documentation. - [ ] In documents I changed, I [added a meta description](https://canonical-starflow.readthedocs-hosted.com/how-to/add-a-page-meta-description/) if one was missing. - [ ] I've updated the relevant release notes.