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[9.0.0] Use comparator when extracting relevant facts for lockfile#27881

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meteorcloudy merged 1 commit intobazelbuild:release-9.0.0from
bazel-io:cp27816-9.0.0
Dec 5, 2025
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[9.0.0] Use comparator when extracting relevant facts for lockfile#27881
meteorcloudy merged 1 commit intobazelbuild:release-9.0.0from
bazel-io:cp27816-9.0.0

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@bazel-io bazel-io commented Dec 5, 2025

ModuleExtensionId is not comparable by itself and needs a comparator. Before this fix, I was able to crash Bazel with this message:

FATAL: bazel crashed due to an internal error. Printing stack trace: java.lang.ClassCastException: class com.google.devtools.build.lib.bazel.bzlmod.ModuleExtensionId cannot be cast to class java.lang.Comparable (com.google.devtools.build.lib.bazel.bzlmod.ModuleExtensionId is in unnamed module of loader 'app'; java.lang.Comparable is in module java.base of loader 'bootstrap')
        at com.google.common.collect.NaturalOrdering.compare(NaturalOrdering.java:29)
        at com.google.common.collect.ImmutableSortedMap.lambda$fromEntries$0(ImmutableSortedMap.java:536)
        at java.base/java.util.TimSort.countRunAndMakeAscending(Unknown Source)
        at java.base/java.util.TimSort.sort(Unknown Source)
        at java.base/java.util.Arrays.sort(Unknown Source)
        at com.google.common.collect.ImmutableSortedMap.fromEntries(ImmutableSortedMap.java:528)
        at com.google.common.collect.ImmutableSortedMap.fromEntries(ImmutableSortedMap.java:495)
        at com.google.common.collect.ImmutableSortedMap.copyOfInternal(ImmutableSortedMap.java:474)
        at com.google.common.collect.ImmutableSortedMap.copyOf(ImmutableSortedMap.java:372)
        at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileModule.afterCommand(BazelLockFileModule.java:135)
        at com.google.devtools.build.lib.runtime.BlazeRuntime.afterCommand(BlazeRuntime.java:734)
        at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.execExclusively(BlazeCommandDispatcher.java:711)
        at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.exec(BlazeCommandDispatcher.java:257)
        at com.google.devtools.build.lib.server.GrpcServerImpl.executeCommand(GrpcServerImpl.java:607)
        at com.google.devtools.build.lib.server.GrpcServerImpl.lambda$run$0(GrpcServerImpl.java:677)
        at io.grpc.Context$1.run(Context.java:566)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)

Fixes #27522

Closes #27816.

PiperOrigin-RevId: 840671327
Change-Id: Ia7eb05be4fd099f0e2711065faf4c344d45265b5

Commit b2587f6

@malt3 @bazel-io
Use comparator when extracting relevant facts for lockfile
f62b9a5 
ModuleExtensionId is not comparable by itself and needs a comparator. Before this fix, I was able to crash Bazel with this message:

```
FATAL: bazel crashed due to an internal error. Printing stack trace: java.lang.ClassCastException: class com.google.devtools.build.lib.bazel.bzlmod.ModuleExtensionId cannot be cast to class java.lang.Comparable (com.google.devtools.build.lib.bazel.bzlmod.ModuleExtensionId is in unnamed module of loader 'app'; java.lang.Comparable is in module java.base of loader 'bootstrap')
        at com.google.common.collect.NaturalOrdering.compare(NaturalOrdering.java:29)
        at com.google.common.collect.ImmutableSortedMap.lambda$fromEntries$0(ImmutableSortedMap.java:536)
        at java.base/java.util.TimSort.countRunAndMakeAscending(Unknown Source)
        at java.base/java.util.TimSort.sort(Unknown Source)
        at java.base/java.util.Arrays.sort(Unknown Source)
        at com.google.common.collect.ImmutableSortedMap.fromEntries(ImmutableSortedMap.java:528)
        at com.google.common.collect.ImmutableSortedMap.fromEntries(ImmutableSortedMap.java:495)
        at com.google.common.collect.ImmutableSortedMap.copyOfInternal(ImmutableSortedMap.java:474)
        at com.google.common.collect.ImmutableSortedMap.copyOf(ImmutableSortedMap.java:372)
        at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileModule.afterCommand(BazelLockFileModule.java:135)
        at com.google.devtools.build.lib.runtime.BlazeRuntime.afterCommand(BlazeRuntime.java:734)
        at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.execExclusively(BlazeCommandDispatcher.java:711)
        at com.google.devtools.build.lib.runtime.BlazeCommandDispatcher.exec(BlazeCommandDispatcher.java:257)
        at com.google.devtools.build.lib.server.GrpcServerImpl.executeCommand(GrpcServerImpl.java:607)
        at com.google.devtools.build.lib.server.GrpcServerImpl.lambda$run$0(GrpcServerImpl.java:677)
        at io.grpc.Context$1.run(Context.java:566)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)
```

Fixes bazelbuild#27522

Closes bazelbuild#27816.

PiperOrigin-RevId: 840671327
Change-Id: Ia7eb05be4fd099f0e2711065faf4c344d45265b5
@bazel-io bazel-io added the team-ExternalDeps External dependency handling, remote repositiories, WORKSPACE file. label Dec 5, 2025
@bazel-io bazel-io requested a review from a team as a code owner December 5, 2025 12:41
@bazel-io bazel-io added the awaiting-review PR is awaiting review from an assigned reviewer label Dec 5, 2025
@bazel-io bazel-io mentioned this pull request Dec 5, 2025
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gemini-code-assist bot commented Dec 5, 2025

Summary of Changes

Hello @bazel-io, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request provides a critical fix for a ClassCastException in Bazel's lockfile generation mechanism. The issue stemmed from the incorrect handling of ModuleExtensionId objects, which are not inherently comparable, when used as keys in sorted maps. By explicitly supplying a lexicographic comparator for these IDs, the system can now correctly process and sort module extension facts, preventing crashes and ensuring the integrity of the lockfile. A new test case has been added to verify the robustness of this solution.

Highlights

  • Bug Fix: ClassCastException: This pull request resolves a java.lang.ClassCastException that occurred during Bazel's lockfile generation. The crash happened because ModuleExtensionId objects, which do not implement Comparable, were being used as keys in an ImmutableSortedMap without an explicit comparator, leading to a runtime error when multiple module extensions provided facts.
  • Comparator Implementation: To address the ClassCastException, the ModuleExtensionId.LEXICOGRAPHIC_COMPARATOR is now explicitly provided to the ImmutableSortedMap.copyOf() method. This ensures that ModuleExtensionId keys are correctly sorted based on their lexicographical order, preventing the crash and ensuring stable lockfile generation.
  • Regression Test Added: A new Python test, testMultipleExtensionsWithFacts, has been introduced. This test case specifically validates that Bazel can successfully build and generate a lockfile when multiple module extensions provide facts, confirming that the ClassCastException regression is resolved.
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Code Review

This pull request effectively resolves a ClassCastException that occurs when processing module extensions with facts. The root cause was correctly identified as creating an ImmutableSortedMap with ModuleExtensionId keys without providing a comparator. The fix, which involves supplying the ModuleExtensionId.LEXICOGRAPHIC_COMPARATOR, is direct and correct. The addition of the testMultipleExtensionsWithFacts regression test is excellent, as it specifically targets the scenario that caused the crash and ensures this issue will not reappear. The changes are of high quality.

@meteorcloudy meteorcloudy added this pull request to the merge queue Dec 5, 2025
Merged via the queue into bazelbuild:release-9.0.0 with commit 05b3774 Dec 5, 2025
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@github-actions github-actions bot removed the awaiting-review PR is awaiting review from an assigned reviewer label Dec 5, 2025
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@meteorcloudy meteorcloudy meteorcloudy approved these changes

@fmeum fmeum Awaiting requested review from fmeum

@SalmaSamy SalmaSamy Awaiting requested review from SalmaSamy

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@malt3 malt3 malt3 approved these changes

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