feat(cargo-anvil): make impact cache inputs injectable

[Evgenii (Vaiz)]

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Add ANVIL_IMPACT_INPUT_DIR to select a read-only cache in consume mode. Cache validation and scope reads use the selected directory. Missing inputs fail instead of falling back to another cache.

The MSRV test reads its committed fixture directly, without copying files or computing impact. Existing assertions for both feature modes and no-MSRV skipping remain.

Unset or empty uses target/anvil/impact/. Compute and off modes ignore the override. Update the design documentation and regenerate the repository recipe and lock checksums.

This removes the setup dependency behind the failure on #162; it does not establish why impact analysis originally returned success without the cache file.

Failure: https://github.com/microsoft/ox-tools/actions/runs/34223762035/job/102053921477

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.5%. Comparing base (3bf8d54) to head (dc8f970).
⚠️ Report is 2 commits behind head on main.

❌ Your project status has failed because the head coverage (97.5%) 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    #169     +/-   ##
=======================================
- Coverage   97.5%   97.5%   -0.1%     
=======================================
  Files        300     300             
  Lines      68538   68538             
=======================================
- Hits       66876   66875      -1     
- Misses      1662    1663      +1     

Flag	Coverage Δ
linux	97.5% <ø> (ø)
linux-arm	97.5% <ø> (+<0.1%)	⬆️
scheduled	?
windows	97.7% <ø> (-0.1%)	⬇️

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[Copilot]

🟢 Approval recommended

The changes are internally consistent across recipe/template/docs and are backed by targeted test updates that exercise the new consume-mode input selection and failure behavior.

Pull request overview

This PR extends cargo-anvil’s impact-scoping “consume” mode to allow selecting an alternate, read-only impact cache directory via ANVIL_IMPACT_INPUT_DIR (e.g., a checked-in fixture), and updates tests/docs/lock artifacts accordingly.

Changes:

• Add ANVIL_IMPACT_INPUT_DIR support in impact cache validation and _anvil-impact-include reads (consume mode only), and fail loudly when the selected cache is missing.
• Update MSRV test flow to consume a committed impact-cache fixture directly (no copying / no impact computation) and strengthen assertions around produced scopes and command invocations.
• Refresh design documentation, generated recipe snapshots, fixtures, and .anvil.lock checksums.

File summaries

File	Description
justfiles/anvil/impact.just	Add injectable input dir for consume-mode cache validation and include-file reads; improve missing-cache diagnostics.
crates/cargo-anvil/templates/justfiles/anvil/impact.just	Mirror the same consume-mode injectable input-dir behavior in the generated template source.
crates/cargo-anvil/docs/design/local.md	Document ANVIL_IMPACT_INPUT_DIR behavior, constraints, and consume-mode semantics.
crates/cargo-anvil/tests/impact.rs	Adjust MSRV test to inject a checked-in cache; add assertions preventing fallback/local-cache creation; add explicit failure coverage for missing injected input.
crates/cargo-anvil/tests/fixtures/msrv-impact-cache/include_required.txt	Add committed fixture include file for required tier.
crates/cargo-anvil/tests/fixtures/msrv-impact-cache/include_modified.txt	Add committed fixture include file for modified tier.
crates/cargo-anvil/tests/fixtures/msrv-impact-cache/include_affected.txt	Add committed fixture include file for affected tier.
crates/cargo-anvil/tests/snapshots/snapshots__local_only.snap	Update generated snapshot to reflect new ANVIL_IMPACT_INPUT_DIR logic and diagnostics.
crates/cargo-anvil/tests/snapshots/snapshots__github_backend.snap	Update generated snapshot to reflect new ANVIL_IMPACT_INPUT_DIR logic and diagnostics.
crates/cargo-anvil/tests/snapshots/snapshots__ado_backend.snap	Update generated snapshot to reflect new ANVIL_IMPACT_INPUT_DIR logic and diagnostics.
.anvil.lock	Update catalog and file checksums after recipe/template regeneration.

Review details

• Files reviewed: 10/11 changed files
• Comments generated: 0
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The changes are consistently applied across the recipe source/template, tests and design docs, and the updated tests cover both the new override behavior and the “missing explicit input must fail” contract.

Review details

• Files reviewed: 10/11 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The behavioral change is scoped and consistently applied across recipe/template/docs/tests, with only minor diagnostic clarity suggestions remaining.

Review details

Suppressed comments (1)

crates/cargo-anvil/templates/justfiles/anvil/impact.just:634

• When _anvil-impact-include fails in consume mode, the message names the missing file but doesn’t call out that ANVIL_IMPACT_INPUT_DIR may be redirecting reads, nor what constitutes a “complete” cache. Mentioning the override and required include files would better guide users to the fix.

    } elseif ($env:ANVIL_IMPACT -eq 'consume') {
        Write-Error "anvil-impact: ANVIL_IMPACT=consume but the input impact cache is missing ($file). Supply a complete impact cache before scoped checks run."
        exit 1

• Files reviewed: 10/11 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes are internally consistent (template + generated recipe + docs + tests) and the new override behavior is guarded by targeted test coverage.

Review details

• Files reviewed: 10/11 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes consistently apply the new consume-mode input override across validation and reads, include clear failure diagnostics, and are backed by targeted test updates and design doc updates.

Review details

• Files reviewed: 16/17 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟡 Changes recommended

anvil-container currently rejects ANVIL_IMPACT_INPUT_DIR even when ANVIL_IMPACT is not consume, which conflicts with the stated “ignored outside consume mode” contract and unnecessarily blocks containerized runs.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 16/17 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

🔵 Needs a closer look

The updated MSRV test assertion compares mismatched types for the captured invocations, so the check needs to be adjusted to compare like-for-like.

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

crates/cargo-anvil/tests/impact.rs:1052

• test_invocations is collected as Vec<&str>, but it is compared against expected, which is an array of Strings. Align the types (and ideally compare two Vec<String>s) so the assertion is well-defined and checks the exact invocations in order.

• Files reviewed: 16/17 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Evgenii (Vaiz)]

On the suppressed comment about crates/cargo-anvil/tests/impact.rs:1052 — I checked this against the code and I don't think there is anything to fix, so I'm leaving it as is.

The types are mismatched in the sense the comment describes: test_invocations is a Vec<&str> and expected is a [String; 2]. But that comparison is well-defined, not accidental. The standard library implements PartialEq<String> for &str, and Vec<A> implements PartialEq<[B; N]> wherever A: PartialEq<B>, so the two compose and assert_eq! compares the elements pairwise, in order, for exact string equality — which is precisely what the test is asserting.

The decisive evidence is that it compiles. Rust performs no implicit conversion here; if the operands did not have a PartialEq impl relating them, this would be a compile error rather than a silently weak assertion. The file builds and the test passes as part of cargo +1.95 test -p cargo-anvil --all-features (21/21 in the impact suite on the current head), so the assertion is both well-typed and exercised.

Collecting into a Vec<String> would allocate two Strings per line to reach the same verdict, so I would rather keep the borrowed form. Happy to change it if a reviewer prefers the symmetry as a readability matter, but I don't want to record it as a correctness fix, because the current assertion already checks the exact invocations in order.