## Summary Stacked on #2940. `snap-build` fails in the `charmcraft` part. The snap builds every dependency from source (`PIP_NO_BINARY: ":all:"`, kept deliberately to work around <https://github.com/canonical/charmcraft/issues/1369>), which pins the build against whatever toolchain the build environment ships. That environment has moved on twice, and both failures are in this one part: 1. pip also builds the Rust build backends from source, and maturin needs a newer rustc than the snap pins: ``` error: rustc 1.85.1 is not supported by the following packages: maturin@1.15.0 requires rustc 1.89 ERROR: Failed to build wheel for maturin ``` 2. protobuf 3.20.3's `setup.py` imports `pkg_resources`, which setuptools removed in 81 (current setuptools is 84), so that sdist cannot build at all: ``` ModuleNotFoundError: No module named 'pkg_resources' ERROR: Failed to build 'protobuf' when getting requirements to build wheel ``` ### Fixes - Pin `cargo`/`rustc` to 1.91 instead of 1.85. 1.91.1 is in the `core22` (jammy) archive for every architecture this snap builds for, and is the same toolchain `hotfix/4.4` pins. - Bump `protobuf` 3.20.3 -> 4.25.8. Both failures are the same class of problem (ancient sdist, modern build tool), so they are fixed together. 4.25.8 is API compatible for this repo's only consumer: `macaroonbakery` requires `protobuf >=3.20.0`, and the 4.x line of that era is a re-versioning of the 3.20 code. Verified locally that the 4.25.8 sdist builds fully on Python 3.10 with setuptools 84. Two alternatives were considered and rejected: - Keeping protobuf 3.20.3 and pinning an older setuptools for the build environment: pip ignores constraints files for build isolation (verified: `--constraint setuptools<81` still installed setuptools 84.0.0 into the isolated env), so this cannot be expressed from the repo. - Keeping protobuf 3.20.3 but allowing its wheel (`PIP_ONLY_BINARY: protobuf`): its only arch-independent wheel is `protobuf-3.20.3-py2.py3-none-any.whl`, i.e. the slower pure-Python implementation, to avoid a version bump. ## Test plan CI: `snap-build` compiles `maturin` and `protobuf` and completes the `charmcraft` part, which also unblocks `snap-tests`. > [!WARNING] > Generated by an automated agent, not a human. 🤖 **BEEP BOOP I'M A TOASTER** _Model:_ `step-5-preview-free` _Harness:_ opencode CLI