Assertion failed in Microsoft.CodeAnalysis.CSharp.SynthesizedClosureEnvironment.AssertIsClosureScopeSyntax

[tmat]

Clone https://github.com/microsoft/Microsoft.Unity.Analyzers, open src\Microsoft.Unity.Analyzers.sln in VS with debug build of Roslyn from main branch. Build the solution.

The build also fails with error MSB6006: "csc.exe" exited with code -2146232797

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Assertion Failed: Abort=Quit, Retry=Debug, Ignore=Continue
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Unexpected value 'VariableDeclarator' of type 'Microsoft.CodeAnalysis.CSharp.SyntaxKind'

   at Roslyn.Utilities.ExceptionUtilities.UnexpectedValue(Object o) in C:\R0\src\Compilers\Core\Portable\InternalUtilities\ExceptionUtilities.cs:line 22

   at Microsoft.CodeAnalysis.CSharp.SynthesizedClosureEnvironment.AssertIsClosureScopeSyntax(SyntaxNode syntaxOpt) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\SynthesizedClosureEnvironment.cs:line 106

   at Microsoft.CodeAnalysis.CSharp.SynthesizedClosureEnvironment..ctor(MethodSymbol topLevelMethod, MethodSymbol containingMethod, Boolean isStruct, SyntaxNode scopeSyntaxOpt, DebugId methodId, DebugId closureId, Nullable`1 rudeEdit) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\SynthesizedClosureEnvironment.cs:line 71

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.<>c__DisplayClass36_0.<SynthesizeClosureEnvironments>g__MakeFrame|1(Scope scope, ClosureEnvironment env) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.cs:line 379

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.<>c__DisplayClass36_0.<SynthesizeClosureEnvironments>b__0(Scope scope) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.cs:line 346

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.Analysis.VisitScopeTree(Scope treeRoot, Action`1 action) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.Analysis.Tree.cs:line 262

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.Analysis.VisitScopeTree(Scope treeRoot, Action`1 action) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.Analysis.Tree.cs:line 266

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.SynthesizeClosureEnvironments(ArrayBuilder`1 closureDebugInfo) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.cs:line 340

   at Microsoft.CodeAnalysis.CSharp.ClosureConversion.Rewrite(BoundStatement loweredBody, NamedTypeSymbol thisType, ParameterSymbol thisParameter, MethodSymbol method, Int32 methodOrdinal, MethodSymbol substitutedSourceMethod, ArrayBuilder`1 lambdaDebugInfoBuilder, ArrayBuilder`1 lambdaRuntimeRudeEditsBuilder, ArrayBuilder`1 closureDebugInfoBuilder, VariableSlotAllocator slotAllocator, TypeCompilationState compilationState, BindingDiagnosticBag diagnostics, HashSet`1 assignLocals) in C:\R0\src\Compilers\CSharp\Portable\Lowering\ClosureConversion\ClosureConversion.cs:line 269

   at Microsoft.CodeAnalysis.CSharp.MethodCompiler.LowerBodyOrInitializer(MethodSymbol method, Int32 methodOrdinal, BoundStatement body, SynthesizedSubmissionFields previousSubmissionFields, TypeCompilationState compilationState, MethodInstrumentation instrumentation, DebugDocumentProvider debugDocumentProvider, ImmutableArray`1& codeCoverageSpans, BindingDiagnosticBag diagnostics, VariableSlotAllocator& lazyVariableSlotAllocator, ArrayBuilder`1 lambdaDebugInfoBuilder, ArrayBuilder`1 lambdaRuntimeRudeEditsBuilder, ArrayBuilder`1 closureDebugInfoBuilder, ArrayBuilder`1 stateMachineStateDebugInfoBuilder, StateMachineTypeSymbol& stateMachineTypeOpt) in C:\R0\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 1437

   at Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethod(MethodSymbol methodSymbol, Int32 methodOrdinal, ProcessedFieldInitializers& processedInitializers, SynthesizedSubmissionFields previousSubmissionFields, TypeCompilationState compilationState) in C:\R0\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 1176

   at Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamedType(NamedTypeSymbol containingType) in C:\R0\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 537

   at Microsoft.CodeAnalysis.CSharp.MethodCompiler.<>c__DisplayClass25_0.<CompileNamedTypeAsync>b__0() in C:\R0\src\Compilers\CSharp\Portable\Compiler\MethodCompiler.cs:line 439

   at Roslyn.Utilities.UICultureUtilities.<>c__DisplayClass5_0.<WithCurrentUICulture>b__0() in C:\R0\src\Compilers\Core\Portable\InternalUtilities\UICultureUtilities.cs:line 139

   at System.Threading.Tasks.Task.Execute()

   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)

   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)

   at System.Threading.Tasks.Task.ExecuteEntry(Boolean bPreventDoubleExecution)

   at System.Threading.ThreadPoolWorkQueue.Dispatch()


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Abort   Retry   Ignore   
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The assertion is triggered when compiling lambda:

Func<CancellationToken, Task<Document>>? action = node switch
{
  BinaryExpressionSyntax bes => ct => ReplaceBinaryExpressionAsync(context.Document, bes, ct),
  InvocationExpressionSyntax ies => ct => ReplaceInvocationExpressionAsync(context.Document, ies, ct),
  _ => null
};

The bound block of the Analysis.Scope is associated with VariableDeclaratorSyntax, which is not an expected closure syntax node.

[sailro]

cc @jbevain