Project variables with curly braces are rejected in app commands: ```yaml apps: my-app: command: bin/${SNAPCRAFT_PROJECT_NAME} ``` ``` App commands must consist of only alphanumeric characters, spaces, and the following characters: / . _ # : $ - ``` This is a regression from #5183, which widened the `bus_name` validator to also cover `command`, `stop_command`, `post_stop_command` and `reload_command`. The character class it uses is taken from snapd's `appContentWhitelist`, and that class is right for snapd — but snapd only ever sees these fields *after* Snapcraft has expanded them, so `{` and `}` never reach it. The model validates while the reference is still literal, so the braces are rejected. Fixes #5500 ## Approach Well-formed `${VAR}` references are removed before snapd's character class is applied. Simply adding `{` and `}` to the class would also fix the reported case, but it would let genuinely malformed values through to snapd, which rejects them later with a less helpful error. Stripping only the variable references keeps the original guard intact: `bin/mkbird{5}`, `bin/${}` and `bin/${SNAPCRAFT PROJECT NAME}` are all still rejected here. `command-chain` has a similar validator, but it predates #5183 and isn't part of this regression, so I've left it alone — happy to include it if you'd prefer. ## Tests - `test_app_command_lexicon_project_variable` covers all five validated fields against a braced reference, a leading reference, two references in one value, and the brace-less `$VAR` form. - `test_app_command_lexicon_bad` gains the three malformed-brace cases above, so the narrowing can't silently regress into "braces are always fine". I didn't add a release-note entry since there's no unreleased notes file on `main` — glad to add one wherever you'd like it. --- - [x] I've followed the [contribution guidelines](https://github.com/canonical/snapcraft/blob/main/CONTRIBUTING.md). - [x] I've signed the [CLA](http://www.ubuntu.com/legal/contributors/). - [ ] I've successfully run `make lint && make test`. - [ ] 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. On the unchecked boxes, to be precise about what I did run: `ruff check` and `ruff format` are clean on both files, and `tests/unit/models/test_projects.py` passes. I haven't completed a full `make lint && make test` locally — `make setup` doesn't finish on my machine because it installs `shfmt` via snap. No documentation changes seemed warranted for a validator fix, so the last three boxes are untouched rather than skipped; say the word if you'd like any of them addressed.