CFE crashes on a conditional expression involving a record

[alexmarkov]

Part of #49713.

Consider the following example:

void main(List<String> args) {
  (int, int) x = (1, 2);
  (int, int) y = (3, 4);
  (int, int) z = args.length > 0 ? x : y;
  print(z);
}

CFE crashes in the following way:

Crash when compiling file://.../foo.dart,
at character offset 88:
type 'RecordType' is not a subtype of type 'InterfaceType' in type cast
#0      StandardBounds.getNullabilityAwareStandardUpperBoundInternal (package:kernel/src/standard_bounds.dart:830:13)
#1      TypeSchemaStandardBounds.getNullabilityAwareStandardUpperBoundInternal (package:front_end/src/fasta/type_inference/standard_bounds.dart:57:18)
#2      StandardBounds._getNullabilityAwareStandardUpperBound (package:kernel/src/standard_bounds.dart:625:12)
#3      StandardBounds.getStandardUpperBound (package:kernel/src/standard_bounds.dart:613:14)
#4      InferenceVisitorImpl.visitConditionalExpression (package:front_end/src/fasta/type_inference/inference_visitor.dart:860:51)
#5      ConditionalExpression.accept1 (package:kernel/ast.dart:7142:9)
#6      InferenceVisitorImpl._inferExpression (package:front_end/src/fasta/type_inference/inference_visitor.dart:136:27)
#7      InferenceVisitorImpl.inferExpression (package:front_end/src/fasta/type_inference/inference_visitor.dart:171:40)
#8      InferenceVisitorImpl.visitVariableDeclaration (package:front_end/src/fasta/type_inference/inference_visitor.dart:6828:27)
#9      VariableDeclaration.accept (package:kernel/ast.dart:11006:43)
#10     InferenceVisitorImpl.inferStatement (package:front_end/src/fasta/type_inference/inference_visitor.dart:107:26)
#11     InferenceVisitorImpl._visitStatements (package:front_end/src/fasta/type_inference/inference_visitor.dart:720:50)
#12     InferenceVisitorImpl.visitBlock (package:front_end/src/fasta/type_inference/inference_visitor.dart:741:31)
#13     Block.accept (package:kernel/ast.dart:9436:43)
#14     InferenceVisitorImpl.inferStatement (package:front_end/src/fasta/type_inference/inference_visitor.dart:107:26)
#15     TypeInferrerImpl.inferFunctionBody (package:front_end/src/fasta/type_inference/type_inferrer.dart:185:17)
#16     BodyBuilder.finishFunction (package:front_end/src/fasta/kernel/body_builder.dart:1327:43)
#17     DietListener.buildFunctionBody (package:front_end/src/fasta/source/diet_listener.dart:1103:19)
#18     DietListener.endTopLevelMethod (package:front_end/src/fasta/source/diet_listener.dart:376:5)
#19     Parser.parseTopLevelMethod (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3480:14)
#20     Parser.parseTopLevelMemberImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3220:14)
#21     Parser.parseTopLevelDeclarationImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:531:14)
#22     Parser.parseUnit (package:_fe_analyzer_shared/src/parser/parser_impl.dart:377:15)
#23     SourceLoader.buildBody (package:front_end/src/fasta/source/source_loader.dart:1166:12)
<asynchronous suspension>
#24     SourceLoader.buildBodies (package:front_end/src/fasta/source/source_loader.dart:663:7)
<asynchronous suspension>
#25     KernelTarget.buildComponent.<anonymous closure> (package:front_end/src/fasta/kernel/kernel_target.dart:620:7)
<asynchronous suspension>
#26     withCrashReporting (package:front_end/src/fasta/crash.dart:122:12)
<asynchronous suspension>
#27     _buildInternal (package:front_end/src/kernel_generator_impl.dart:202:19)
<asynchronous suspension>
#28     withCrashReporting (package:front_end/src/fasta/crash.dart:122:12)
<asynchronous suspension>
#29     generateKernel.<anonymous closure> (package:front_end/src/kernel_generator_impl.dart:47:12)
<asynchronous suspension>
#30     generateKernel (package:front_end/src/kernel_generator_impl.dart:46:10)
<asynchronous suspension>
#31     kernelForModule (package:front_end/src/api_prototype/kernel_generator.dart:100:11)
<asynchronous suspension>
#32     SingleShotCompilerWrapper.compileInternal (file://.../pkg/vm/bin/kernel_service.dart:412:11)
<asynchronous suspension>
#33     Compiler.compile.<anonymous closure> (file://.../pkg/vm/bin/kernel_service.dart:221:45)
<asynchronous suspension>
#34     _processLoadRequest (file://.../pkg/vm/bin/kernel_service.dart:914:37)
<asynchronous suspension>


#0      DietListener.buildFunctionBody (package:front_end/src/fasta/source/diet_listener.dart:1107:7)
#1      DietListener.endTopLevelMethod (package:front_end/src/fasta/source/diet_listener.dart:376:5)
#2      Parser.parseTopLevelMethod (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3480:14)
#3      Parser.parseTopLevelMemberImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3220:14)
#4      Parser.parseTopLevelDeclarationImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:531:14)
#5      Parser.parseUnit (package:_fe_analyzer_shared/src/parser/parser_impl.dart:377:15)
#6      SourceLoader.buildBody (package:front_end/src/fasta/source/source_loader.dart:1166:12)
<asynchronous suspension>
#7      SourceLoader.buildBodies (package:front_end/src/fasta/source/source_loader.dart:663:7)
<asynchronous suspension>
#8      KernelTarget.buildComponent.<anonymous closure> (package:front_end/src/fasta/kernel/kernel_target.dart:620:7)
<asynchronous suspension>
#9      withCrashReporting (package:front_end/src/fasta/crash.dart:122:12)
<asynchronous suspension>
#10     _buildInternal (package:front_end/src/kernel_generator_impl.dart:202:19)
<asynchronous suspension>
#11     withCrashReporting (package:front_end/src/fasta/crash.dart:122:12)
<asynchronous suspension>
#12     generateKernel.<anonymous closure> (package:front_end/src/kernel_generator_impl.dart:47:12)
<asynchronous suspension>
#13     generateKernel (package:front_end/src/kernel_generator_impl.dart:46:10)
<asynchronous suspension>
#14     kernelForModule (package:front_end/src/api_prototype/kernel_generator.dart:100:11)
<asynchronous suspension>
#15     SingleShotCompilerWrapper.compileInternal (file://.../pkg/vm/bin/kernel_service.dart:412:11)
<asynchronous suspension>
#16     Compiler.compile.<anonymous closure> (file://.../pkg/vm/bin/kernel_service.dart:221:45)
<asynchronous suspension>
#17     _processLoadRequest (file://.../pkg/vm/bin/kernel_service.dart:914:37)
<asynchronous suspension>

While type inference is not implemented for records yet, is it possible to add a trivial inference for conditional expressions in case both variants have the same type, so that we could still write conditional expressions involving records?

/cc @johnniwinther @chloestefantsova

[chloestefantsova]

Thanks for reporting that. I'm working on a fix at https://dart-review.googlesource.com/c/sdk/+/258005