[9.3.0] Avoid cc toolchain fieldValue access NPE (https://github.com/bazelbuild/bazel/pull/30502) (#30551) ### Description Interpret null fieldValue in cc toolchain variable info structure enumeration with NoneType behavior to avoid NPE ### Motivation A CC Toolchain Variables Info struct member field may be absent, resulting in a null fieldValue, and attempted access in asVariableValue(). This NPE was observed with rules_rs at latest 0.0.98, and occurs because of the intolerance of null in Java's switch expression: ``` FATAL: bazel crashed due to an internal error. Printing stack trace: java.lang.RuntimeException: Unrecoverable error while evaluating node 'ToolchainDependencyConfiguredTargetKey{label=@@rules_rs++toolchains+default_rust_toolchains//:linux_x86_64_1_94_0_rust_toolchain, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c], executionPlatformLabel=//platform:label}' (requested by nodes 'ConfiguredTargetKey{label=//tools/pathstrip:pathstrip, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', 'ConfiguredTargetKey{label=//tools/toolchains/musl/test:hello_rs, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', 'ConfiguredTargetKey{label=@@rules_rs++rules_rust+rules_rust//ffi/rs:empty_allocator_libraries, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', 'ConfiguredTargetKey{label=@@rules_rs++crate+crates__clap-4.6.1//:clap, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', 'ConfiguredTargetKey{label=@@rules_rs++crate+crates__clap_derive-4.6.1//:clap_derive, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', 'ConfiguredTargetKey{label=@@rules_rs++crate+crates__clap_builder-4.6.0//:clap_builder, config=BuildConfigurationKey[a337dd2dab759f1f66b2c79b8b8f48ef5c1353e0b6cdeded439a4ecf9bc4019c]}', ...) at com.google.devtools.build.skyframe.AbstractParallelEvaluator$Evaluate.run(AbstractParallelEvaluator.java:552) at com.google.devtools.build.lib.concurrent.AbstractQueueVisitor$WrappedRunnable.run(AbstractQueueVisitor.java:435) at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute(Unknown Source) at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.compute(Unknown Source) at java.base/java.util.concurrent.ForkJoinTask$InterruptibleTask.exec(Unknown Source) at java.base/java.util.concurrent.ForkJoinTask.doExec(Unknown Source) at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(Unknown Source) at java.base/java.util.concurrent.ForkJoinPool.runWorker(Unknown Source) at java.base/java.util.concurrent.ForkJoinWorkerThread.run(Unknown Source) Caused by: java.lang.NullPointerException at java.base/java.util.Objects.requireNonNull(Unknown Source) at com.google.devtools.build.lib.rules.cpp.CcToolchainVariables.asVariableValue(CcToolchainVariables.java:826) at com.google.devtools.build.lib.rules.cpp.CcToolchainVariables$StarlarkStructureAdapter.getFieldValue(CcToolchainVariables.java:886) at com.google.devtools.build.lib.rules.cpp.CcToolchainVariables.getStructureVariable(CcToolchainVariables.java:425) at com.google.devtools.build.lib.rules.cpp.CcToolchainVariables.lookupVariable(CcToolchainVariables.java:371) at com.google.devtools.build.lib.rules.cpp.CcToolchainVariables.getVariable(CcToolchainVariables.java:330) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$FlagGroup.expand(CcToolchainFeatures.java:225) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$FlagGroup.expand(CcToolchainFeatures.java:229) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$FlagGroup.expandCommandLine(CcToolchainFeatures.java:296) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$FlagSet.expandCommandLine(CcToolchainFeatures.java:344) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$Feature.expandCommandLine(CcToolchainFeatures.java:466) at com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures$FeatureConfiguration.getCommandLine(CcToolchainFeatures.java:931) at com.google.devtools.build.lib.rules.cpp.LinkCommandLine.getParamCommandLine(LinkCommandLine.java:105) at com.google.devtools.build.lib.rules.cpp.LinkCommandLine.arguments(LinkCommandLine.java:164) at com.google.devtools.build.lib.rules.cpp.LinkCommandLine.arguments(LinkCommandLine.java:42) at com.google.devtools.build.lib.actions.AbstractCommandLine.addToFingerprint(AbstractCommandLine.java:61) at com.google.devtools.build.lib.actions.CommandLines.addToFingerprint(CommandLines.java:186) at com.google.devtools.build.lib.analysis.actions.SpawnAction.computeKey(SpawnAction.java:404) at com.google.devtools.build.lib.actions.ActionKeyComputer.getKey(ActionKeyComputer.java:43) at com.google.devtools.build.lib.actions.Actions.canBeShared(Actions.java:92) at com.google.devtools.build.lib.actions.Actions.canBeSharedLogForPotentialFalsePositives(Actions.java:130) at com.google.devtools.build.lib.actions.Actions.verifyGeneratingActionKeys(Actions.java:218) at com.google.devtools.build.lib.actions.Actions.assignOwnersAndThrowIfConflictMaybeToleratingSharedActions(Actions.java:261) at com.google.devtools.build.lib.actions.Actions.assignOwnersAndThrowIfConflictToleratingSharedActions(Actions.java:196) at com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder.build(RuleConfiguredTargetBuilder.java:279) at com.google.devtools.build.lib.analysis.starlark.StarlarkRuleConfiguredTargetUtil.createTarget(StarlarkRuleConfiguredTargetUtil.java:199) at com.google.devtools.build.lib.analysis.ConfiguredTargetFactory.createRule(ConfiguredTargetFactory.java:476) at com.google.devtools.build.lib.analysis.ConfiguredTargetFactory.createConfiguredTarget(ConfiguredTargetFactory.java:240) at com.google.devtools.build.lib.skyframe.SkyframeBuildView.createConfiguredTarget(SkyframeBuildView.java:1398) at com.google.devtools.build.lib.skyframe.ConfiguredTargetFunction.createConfiguredTarget(ConfiguredTargetFunction.java:453) at com.google.devtools.build.lib.skyframe.ConfiguredTargetFunction.compute(ConfiguredTargetFunction.java:371) at com.google.devtools.build.skyframe.AbstractParallelEvaluator$Evaluate.run(AbstractParallelEvaluator.java:471) ... 8 more ``` Solution adopted in this change was to consider asVariableValue case of 'NoneType' equivalent to null response, having "the same behavior as omitted field." Bazel seems otherwise unperturbed by the null response here, resulting in successful builds. ### Build API Changes No ### Release Notes RELNOTES: None Closes #30502. PiperOrigin-RevId: 956561096 Change-Id: Ic625d4e49dd1f7c014a906330ac764d6e505ef34 Commit https://github.com/bazelbuild/bazel/commit/29a68ab937b274ec867f6287352485f48eba85a3 Co-authored-by: George Gensure <werkt0@gmail.com> Co-authored-by: Ian (Hee) Cha <heec@google.com>
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