fix(cargo-anvil): make stable toolchains deterministic

[martin-kolinek]

🤖 Fixes runner-dependent stable Rust selection in cargo-anvil and adds explicit MSRV testing.

What changed

• resolve stable checks from RUSTUP_TOOLCHAIN, then a selecting root rust-toolchain/rust-toolchain.toml, then the root MSRV
• fail instead of inheriting a runner image's moving stable toolchain
• preserve full toolchain-file behavior, including targets, components, and profile
• validate that MSRV fallback is uniform across workspace packages
• run affected-package unit and integration tests under every declared root MSRV with all features and default features
• execute MSRV tests across the same four GitHub and two ADO platform legs as ordinary PR tests so cfg-gated configurations are covered
• allow internal builds to map the public MSRV to a provisioned toolchain through ANVIL_MSRV_TOOLCHAIN
• apply deterministic selection before compiler/cache setup in GitHub Actions, Azure Pipelines, and container builds
• update design docs, generated artifacts, snapshots, and resolver regression coverage

Adopter migration

Ambient runner stable is no longer accepted. Adopters must provide one of:

• a root [workspace.package].rust-version or [package].rust-version shared by every workspace package
• a selecting root rust-toolchain or rust-toolchain.toml
• a preconfigured RUSTUP_TOOLCHAIN

Workspaces with missing or heterogeneous package MSRVs cannot use MSRV fallback and must select a catalog toolchain explicitly. Internal builds can override public selection with RUSTUP_TOOLCHAIN and map the public MSRV test run to a provisioned compiler with ANVIL_MSRV_TOOLCHAIN.

Motivation

Oxidizer PR #698 passed the legacy Rust 1.96.1 job but failed Anvil on a Windows ARM runner that had inherited Rust 1.98.0 and its new Clippy lints. Stable checks should not change behavior based on runner image rollout timing.

Coverage executes the ordinary test suite on the catalog nightly. The dedicated pr-msrv group runs in parallel and ensures that the same affected unit and integration tests continue to compile and pass on the minimum supported compiler across every supported host configuration.

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.7%. Comparing base (48c5311) to head (e7c4bd3).
⚠️ Report is 1 commits behind head on main.

❌ Your project status has failed because the head coverage (97.7%) is below the target coverage (100.0%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #109      +/-   ##
========================================
- Coverage   99.9%   97.7%    -2.3%     
========================================
  Files        135     286     +151     
  Lines      17470   62174   +44704     
========================================
+ Hits       17469   60753   +43284     
- Misses         1    1421    +1420     

Flag	Coverage Δ
windows	97.8% <100.0%> (?)

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[Copilot]

Pull request overview

This PR makes cargo-anvil’s “stable” toolchain selection deterministic (no longer inheriting whatever stable happens to be on a runner image), adds an explicit PR MSRV test group, and updates generated workflow/container assets plus design docs to reflect the new selection rules.

Changes:

• Introduce a stable-toolchain resolver that prefers RUSTUP_TOOLCHAIN, then a root rust-toolchain{.toml}, then root MSRV from Cargo.toml, and thread that selection through stable cargo/rust invocations.
• Add pr-msrv group (anvil-msrv-test) and wire it into local groups plus GitHub Actions/Azure Pipelines templates.
• Update container identity inputs and design/docs to reflect the new deterministic selection and MSRV behavior.

Reviewed changes

Copilot reviewed 96 out of 97 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
justfiles/anvil/versions.just	Add _anvil_stable_toolchain_args selector used by stable commands.
justfiles/anvil/tools.just	Add stable resolver/install primitive; route stable cargo invocations through selected toolchain; add MSRV validation support.
justfiles/anvil/mod.just	Import new MSRV check/group.
justfiles/anvil/impact.just	Ensure impact snapshots/metadata run under the same selected stable toolchain.
justfiles/anvil/groups/pr-slow.just	Include pr-msrv in the local slow umbrella and setup/validate graphs.
justfiles/anvil/groups/pr-msrv.just	New group: runs MSRV tests.
justfiles/anvil/checks/spellcheck.just	Run spellcheck via selected stable toolchain.
justfiles/anvil/checks/semver-check.just	Run cargo metadata/semver-checks via selected stable toolchain.
justfiles/anvil/checks/readme-check.just	Run metadata/doc2readme via selected stable toolchain.
justfiles/anvil/checks/mutants-full.just	Run mutants via selected stable toolchain.
justfiles/anvil/checks/mutants-diff.just	Run mutants via selected stable toolchain.
justfiles/anvil/checks/msrv-test.just	New check: affected-package tests under declared MSRV.
justfiles/anvil/checks/loom.just	Run metadata/tests via selected stable toolchain; setup depends on stable provisioning.
justfiles/anvil/checks/llvm-cov.just	Run metadata/coverage-gate via selected stable toolchain.
justfiles/anvil/checks/license-headers.just	Run heather via selected stable toolchain.
justfiles/anvil/checks/external-types.just	Run metadata via selected stable toolchain.
justfiles/anvil/checks/examples.just	Run examples build via selected stable toolchain; setup depends on stable provisioning.
justfiles/anvil/checks/ensure-no-default-features.just	Run ensure-no-default-features via selected stable toolchain.
justfiles/anvil/checks/ensure-no-cyclic-deps.just	Run ensure-no-cyclic-deps via selected stable toolchain.
justfiles/anvil/checks/doc-test.just	Run doctests via selected stable toolchain; setup depends on stable provisioning.
justfiles/anvil/checks/doc-build.just	Run doc build via selected stable toolchain; setup depends on stable provisioning.
justfiles/anvil/checks/deny.just	Run deny via selected stable toolchain.
justfiles/anvil/checks/clippy.just	Run clippy via selected stable toolchain.
justfiles/anvil/checks/cargo-sort.just	Run cargo-sort via selected stable toolchain.
justfiles/anvil/checks/cargo-hack.just	Run cargo-hack via selected stable toolchain.
justfiles/anvil/checks/careful.just	Use explicit nightly toolchain for cargo clean in careful flow.
justfiles/anvil/checks/bolero.just	Run metadata via selected stable toolchain.
justfiles/anvil/checks/bench.just	Run benches via selected stable toolchain; setup depends on stable provisioning.
justfiles/anvil/checks/audit.just	Run audit via selected stable toolchain.
justfiles/anvil/checks/aprz.just	Run aprz via selected stable toolchain.
crates/cargo-anvil/tests/schemas.rs	Expect new anvil-pr-msrv recipe in emitted recipe list.
crates/cargo-anvil/tests/recipe_contracts.rs	Adjust fixtures/shelling to support stable-toolchain arg arrays and new resolver behavior.
crates/cargo-anvil/tests/impact.rs	Update impact tests for stable toolchain selection and add MSRV test coverage.
crates/cargo-anvil/tests/container_upgrade.rs	Ensure upgrade removes retired legacy resolver artifact.
crates/cargo-anvil/tests/container_customization.rs	Stabilize container customization tests by pinning RUSTUP_TOOLCHAIN in invocations.
crates/cargo-anvil/templates/justfiles/anvil/versions.just	Template mirror of stable toolchain selector.
crates/cargo-anvil/templates/justfiles/anvil/tools.just	Template mirror of stable resolver/provisioning changes.
crates/cargo-anvil/templates/justfiles/anvil/mod.just	Template mirror of new imports.
crates/cargo-anvil/templates/justfiles/anvil/impact.just	Template mirror of deterministic toolchain usage in impact.
crates/cargo-anvil/templates/justfiles/anvil/groups/pr-slow.just	Template mirror of pr-msrv wiring.
crates/cargo-anvil/templates/justfiles/anvil/groups/pr-msrv.just	New template group for MSRV tests.
crates/cargo-anvil/templates/justfiles/anvil/checks/spellcheck.just	Template mirror: stable toolchain for spellcheck.
crates/cargo-anvil/templates/justfiles/anvil/checks/semver-check.just	Template mirror: stable toolchain for semver-check.
crates/cargo-anvil/templates/justfiles/anvil/checks/readme-check.just	Template mirror: stable toolchain for readme check.
crates/cargo-anvil/templates/justfiles/anvil/checks/mutants-full.just	Template mirror: stable toolchain for mutants-full.
crates/cargo-anvil/templates/justfiles/anvil/checks/mutants-diff.just	Template mirror: stable toolchain for mutants-diff.
crates/cargo-anvil/templates/justfiles/anvil/checks/msrv-test.just	New template check for MSRV tests.
crates/cargo-anvil/templates/justfiles/anvil/checks/loom.just	Template mirror: stable toolchain for loom + setup dependency update.
crates/cargo-anvil/templates/justfiles/anvil/checks/llvm-cov.just	Template mirror: stable toolchain for llvm-cov metadata/gate.
crates/cargo-anvil/templates/justfiles/anvil/checks/license-headers.just	Template mirror: stable toolchain for heather.
crates/cargo-anvil/templates/justfiles/anvil/checks/external-types.just	Template mirror: stable toolchain for metadata.
crates/cargo-anvil/templates/justfiles/anvil/checks/examples.just	Template mirror: stable toolchain for examples + setup dependency update.
crates/cargo-anvil/templates/justfiles/anvil/checks/ensure-no-default-features.just	Template mirror: stable toolchain for ensure-no-default-features.
crates/cargo-anvil/templates/justfiles/anvil/checks/ensure-no-cyclic-deps.just	Template mirror: stable toolchain for ensure-no-cyclic-deps.
crates/cargo-anvil/templates/justfiles/anvil/checks/doc-test.just	Template mirror: stable toolchain for doc-test + setup dependency update.
crates/cargo-anvil/templates/justfiles/anvil/checks/doc-build.just	Template mirror: stable toolchain for doc-build + setup dependency update.
crates/cargo-anvil/templates/justfiles/anvil/checks/deny.just	Template mirror: stable toolchain for deny.
crates/cargo-anvil/templates/justfiles/anvil/checks/clippy.just	Template mirror: stable toolchain for clippy.
crates/cargo-anvil/templates/justfiles/anvil/checks/cargo-sort.just	Template mirror: stable toolchain for cargo-sort.
crates/cargo-anvil/templates/justfiles/anvil/checks/cargo-hack.just	Template mirror: stable toolchain for cargo-hack.
crates/cargo-anvil/templates/justfiles/anvil/checks/careful.just	Template mirror: explicit nightly toolchain for careful clean.
crates/cargo-anvil/templates/justfiles/anvil/checks/bolero.just	Template mirror: stable toolchain for metadata.
crates/cargo-anvil/templates/justfiles/anvil/checks/bench.just	Template mirror: stable toolchain for bench + setup dependency update.
crates/cargo-anvil/templates/justfiles/anvil/checks/audit.just	Template mirror: stable toolchain for audit.
crates/cargo-anvil/templates/justfiles/anvil/checks/aprz.just	Template mirror: stable toolchain for aprz.
crates/cargo-anvil/templates/github/setup-action.yml	Bootstrap just before resolving stable rustc version; update cache key inputs.
crates/cargo-anvil/templates/github/pr-impl-workflow.yml	Add pr-msrv job matrix to reusable PR workflow.
crates/cargo-anvil/templates/anvil/container/image-id.sh	Include Cargo.toml + optional toolchain files as image identity inputs.
crates/cargo-anvil/templates/anvil/container/image-id.ps1	Same as above for PowerShell.
crates/cargo-anvil/templates/anvil/container/Containerfile.dockerignore	Allow-list Cargo.toml and rust-toolchain.
crates/cargo-anvil/templates/anvil/container/Containerfile	Remove hard requirement for rust-toolchain.toml.
crates/cargo-anvil/templates/ado/steps/setup.yml	Bootstrap just + stable provisioning before capturing version; update cache key inputs.
crates/cargo-anvil/templates/ado/pr-stages.yml	Add pr_msrv stage parallel to other PR slow stages.
crates/cargo-anvil/src/run.rs	Register new pr-msrv ADO step in generated artifact list.
crates/cargo-anvil/src/lib.rs	Update crate docs for new toolchain/MSRV requirements and PR group topology.
crates/cargo-anvil/src/anvil/artifacts/mod.rs	Classify pr-msrv as impact-consuming.
crates/cargo-anvil/src/anvil/artifacts/github.rs	Add pr-msrv group; assert setup now uses stable version capture helper.
crates/cargo-anvil/src/anvil/artifacts/container.rs	Update container image-id fixtures/inputs and assertions for new contract.
crates/cargo-anvil/src/anvil/artifacts/ado.rs	Add pr-msrv group/stage wiring and setup ordering assertions.
crates/cargo-anvil/README.md	Regenerated README reflecting new requirements and group topology.
crates/cargo-anvil/docs/design/README.md	Update design overview: toolchain ownership/selection and group list.
crates/cargo-anvil/docs/design/local.md	Document deterministic stable selection, setup graph changes, and new pr-msrv.
crates/cargo-anvil/docs/design/github.md	Document GitHub workflow changes and deterministic stable provisioning.
crates/cargo-anvil/docs/design/containers.md	Update container contract and identity inputs for MSRV/toolchain selection.
crates/cargo-anvil/docs/design/checks.md	Add pr-msrv group + msrv-test check and document stable selection semantics.
crates/cargo-anvil/docs/design/ado.md	Document ADO stage topology including pr_msrv and stable provisioning behavior.
.github/workflows/anvil-pr-impl.yml	Add pr-msrv job to this repo’s workflow.
.github/actions/anvil-setup/action.yml	Bootstrap just before stable version capture; update cache key inputs.
.anvil/container/image-id.sh	Repo’s generated container identity script updated for new inputs.
.anvil/container/image-id.ps1	Repo’s generated container identity script updated for new inputs.
.anvil/container/Containerfile.dockerignore	Repo’s generated dockerignore allow-list updated.
.anvil/container/Containerfile	Repo’s generated containerfile updated to remove toolchain.toml requirement.
.anvil.lock	Update catalog checksum + tracked file checksums after regeneration.

Suppressed comments (2)

justfiles/anvil/tools.just:614

• _install-component always runs rustup component add --toolchain $selectedStableToolchain ... for the default toolchain. If _anvil_stable_toolchain_args ever evaluates to an empty/multi-element array, $selectedStableToolchain stays $null and this invocation becomes invalid (--toolchain with a missing value).
  crates/cargo-anvil/templates/justfiles/anvil/tools.just:614
• _install-component always runs rustup component add --toolchain $selectedStableToolchain ... for the default toolchain. If _anvil_stable_toolchain_args ever evaluates to an empty/multi-element array, $selectedStableToolchain stays $null and this invocation becomes invalid (--toolchain with a missing value) in generated trees.

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[martin-kolinek]

Does this need to be so complicated and long? Feels like what we're doing should be a simple check for file existence and if it doesn't exist, pull a value from cargo metadata. Why does it need 350 lines of powershell?

[martin-kolinek]

🤖 Simplified in e7c4bd3. Anvil no longer parses rust-toolchain(.toml) or replays its profile, components, and targets; rustup owns all of that natively. The resolver now checks for a root toolchain file and otherwise handles the MSRV fallback, setup, internal mapping, and workspace validation. The small root rust-version read remains only to bootstrap the explicit compiler needed to run cargo metadata without depending on an ambient default.

[martin-kolinek]

Is there a way to ask cargo about this rather than trying to parse rust-toolchain/rust-toolchain.toml?

[martin-kolinek]

🤖 Cargo can authoritatively resolve package rust_version values, but it does not own rust-toolchain(.toml)—rustup does. In e7c4bd3, repository toolchain files are therefore delegated to rustup show active-toolchain, while workspace compatibility comes from cargo +<root-msrv> metadata. We retain only the minimal root-manifest read needed to discover that bootstrap MSRV; asking Cargo for it first would require choosing an ambient compiler before the deterministic compiler is known.

[martin-kolinek]

🤖: Repository paths containing ( corrupt the resolved toolchain name, while paths containing [ or ] make toolchain resolution fail before it runs.

Split rustup show active-toolchain at the first ( marker, and use Push-Location -LiteralPath $RepoRoot at both resolver call sites.

rustup includes the toolchain-file path in its reason suffix. With a checkout such as repo (fork), LastIndexOf(' (') finds the delimiter inside that path and emits a garbage +toolchain argument, breaking every stable Cargo/Rust command. Separately, Push-Location $RepoRoot treats brackets as wildcards; this occurs here and in tools.just, so an existing checkout such as br[x] cannot be entered during command selection or setup. The current shim fixtures exercise spaces and apostrophes but neither boundary.