[sbomer]

Replay linker diagnostics through normal task logging on cache hits, so MSBuild's current warning policy still applies. Previously, a successful warning-producing invocation could seed the cache and a later -warnaserror build would incorrectly succeed because the hit omitted the warnings.

This is the same class of issue as dotnet/roslyn#86198.

Note

This content was created with assistance from AI.

[azure-pipelines]

Azure Pipelines:
Successfully started running 4 pipeline(s).
12 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

[Copilot]

🔵 Needs a closer look

Human confirmation is needed for warning escalation against real MSBuild because builds and regression tests were not run during this review.

No open issues 🎉

What changed in this PR

This PR makes ILLink task cache hits replay linker diagnostics through normal task logging, allowing MSBuild’s current warning policy to apply to cached results.

Changes:

• Capture linker output and persist it with integrity metadata in cache entries.
• Replay diagnostics after successful restoration and fail cache hits when logging reports errors.
• Add regression coverage for warning policies, malformed diagnostics, and restore failures, and update cache documentation.

File	Description
src/​tools/​illink/​test/​ILLink.Tasks.Tests/​Mock.cs	Records warnings and adds a warning-policy build engine mock.
src/​tools/​illink/​test/​ILLink.Tasks.Tests/​ILLink.Tasks.Tests.cs	Adds diagnostic replay, warning escalation, and cache validation tests.
src/​tools/​illink/​src/​ILLink.Tasks/​LinkTask.cs	Captures tool output and replays it using normal task logging.
src/​tools/​illink/​src/​ILLink.Tasks/​ILLinkCache.cs	Stores, validates, and restores cached diagnostics.
docs/​tools/​illink/​illink-tasks.md	Documents diagnostic replay and current warning-policy behavior.
docs/​design/​tools/​illink/​task-cache.md	Updates cache interfaces, entry layout, and replay guarantees.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Cached message importance can override current task logging settings and hide output that fresh execution would display.

No open issues 🎉

1 previously missed issue

In code that hasn't changed since last review

Cache replay ignores current output importance settings

src/​tools/​illink/​src/​ILLink.Tasks/​ILLinkCache.cs:142

Replaying the saved importance ignores the current StandardOutputImportance and StandardErrorImportance, neither of which is included in TryComputeCacheKey. An entry populated with stdout at Low still replays at Low after the caller requests High, hiding ordinary messages that a fresh invocation would display. Include these settings in the cache key, or preserve each line's originating stream and apply its current importance during replay.

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

The new tests were not executed, leaving warning-policy behavior under a real MSBuild host unverified and requiring human confirmation.

No open issues 🎉

_{Review effort: Balanced}

[Copilot]

🔵 Needs a closer look

Asynchronous output capture and MSBuild warning-policy parity need execution-level validation; builds and tests were not run.

No open issues 🎉

_{Review effort: Balanced}