Fix for Build Requests with Different Flags Not Correctly Scheduled

[YuliiaKovalova]

Fixes #11701

Context

When two build requests with the same configuration ID and targets arrive in the scheduler, the second one is expected to be satisfied from the cache with results from the first request. However, the current implementation doesn't properly account for differing BuildRequestDataFlags between these requests, leading to potential deadlocks.

Problem

If the first request builds successfully but isn't cached (due to exceptions or skipped targets), the second request can get "orphaned" in the scheduler - it's not executed and doesn't send a proper completion callback. This causes Visual Studio to hang indefinitely waiting for a response that never comes.

Changes Made

• Modified the scheduler to properly handle cases where a request's results should be in the cache but aren't
• Added detailed comments explaining the previously problematic behavior that caused VS deadlocks
• Ensured that when cache misses occur, the unscheduled request remains in the queue and gets picked up in the next scheduling pass for proper rebuilding

Testing

• Added unit tests that verify correct handling of build requests with different flags

[Copilot]

Pull Request Overview

This PR updates the scheduler to correctly handle duplicate build requests with the same configuration ID but different build flags by rescheduling the second request when the cache key differs. It also adjusts the reporting logic to mark completed requests earlier and enhances unit tests accordingly.

• In Scheduler.ReportResult, add logic to reschedule on cache miss and move the completion call into the cache-hit branch.
• Fix a typo in a log comment and remove stale all-caps comment.
• Enable previously skipped scheduler tests, introduce a DefaultConfigId constant, broaden CreateBuildRequest overloads, and add two new tests covering duplicate-request scenarios.

Reviewed Changes

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

File	Description
src/Build/BackEnd/Components/Scheduler/Scheduler.cs	Handle cache misses by rescheduling duplicate requests; fix comment
src/Build.UnitTests/BackEnd/Scheduler_Tests.cs	Un-skip many tests, introduce DefaultConfigId, extend helpers, add new duplicate-request tests

Comments suppressed due to low confidence (3)

src/Build.UnitTests/BackEnd/Scheduler_Tests.cs:872

• [nitpick] The new test names use an underscore and the prefix ReportResultTest_, which differs from the existing TestXxx pattern. Consider renaming to match the established naming convention.

public void ReportResultTest_NoCacheHitForDupes()

src/Build.UnitTests/BackEnd/Scheduler_Tests.cs:878

• The responses variable is assigned but never used or asserted against. Either remove it or add assertions to validate the blocked request behavior.

List<ScheduleResponse> responses = [.. _scheduler.ReportRequestBlocked(2, new BuildRequestBlocker(-1, Array.Empty<string>(), [duplicateRequest]))];

src/Build.UnitTests/BackEnd/Scheduler_Tests.cs:878

• Using the C# 12 collection expression here produces an array, not a List, so this assignment will fail. Consider calling .ToList() on the enumerable or using new List<ScheduleResponse>(...).

List<ScheduleResponse> responses = [.. _scheduler.ReportRequestBlocked(2, new BuildRequestBlocker(-1, Array.Empty<string>(), [duplicateRequest]))];

[rainersigwald]

/backport to vs17.14

[github-actions]

Started backporting to vs17.14: https://github.com/dotnet/msbuild/actions/runs/16378306218

[github-actions]

@rainersigwald backporting to "vs17.14" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: update the case in scheduler of reporting unscheduled overlapping results
Applying: adjust the handling of cache miss in scheduler
Using index info to reconstruct a base tree...
M	.editorconfig
M	src/Build.UnitTests/BackEnd/Scheduler_Tests.cs
M	src/Build/BackEnd/BuildManager/BuildManager.cs
M	src/Build/BackEnd/Components/Scheduler/Scheduler.cs
Falling back to patching base and 3-way merge...
Auto-merging .editorconfig
CONFLICT (content): Merge conflict in .editorconfig
Auto-merging src/Build.UnitTests/BackEnd/Scheduler_Tests.cs
Auto-merging src/Build/BackEnd/BuildManager/BuildManager.cs
Auto-merging src/Build/BackEnd/Components/Scheduler/Scheduler.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0002 adjust the handling of cache miss in scheduler
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!