C# generation throws an exception when the Q# code uses an invalid identifier

[bamarsha]

When I use an invalid identifier:

@EntryPoint()
function Main() : Unit {
    Foo(); // not defined
}

The Q# compiler rejects it, which is good:

C:/Users/samarsha/Desktop/Project/Program.qs(4,9): error QS5022: No identifier with the name "Foo" exists.

However, C# generation tries to run anyway, which is bad:

  System.Exception: Received InvalidIdentifier
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.StatementBuilder.buildId(Identifier id) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 425
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.StatementBuilder.buildExpression(TypedExpression ex) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 346
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.StatementBuilder.buildApply(ResolvedType returnType, TypedExpression op, TypedExpression args) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 538
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.StatementBuilder.buildExpression(TypedExpression ex) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 384
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.StatementBuilder.OnExpressionStatement(TypedExpression node) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 611
     at Microsoft.Quantum.QsCompiler.Transformations.Core.StatementKindTransformationBase.OnStatementKind(QsStatementKind kind)
     at Microsoft.Quantum.QsCompiler.Transformations.Core.StatementTransformationBase.OnStatement(QsStatement stm)
     at Microsoft.FSharp.Collections.Internal.IEnumerator.map@75.DoMoveNext(b& curr) in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 81 
     at Microsoft.FSharp.Collections.Internal.IEnumerator.MapEnumerator`1.System-Collections-IEnumerator-MoveNext() in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 68
     at Microsoft.FSharp.Collections.SeqModule.Iterate[T](FSharpFunc`2 action, IEnumerable`1 source) in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 494
     at Microsoft.Quantum.QsCompiler.Transformations.Core.StatementTransformationBase.OnScope(QsScope scope)
     at Microsoft.Quantum.QsCompiler.Transformations.Core.NamespaceTransformationBase.OnProvidedImplementation(QsTuple`1 argTuple, QsScope body)
     at Microsoft.Quantum.QsCompiler.Transformations.Core.NamespaceTransformationBase.OnSpecializationImplementation(SpecializationImplementation implementation)
     at Microsoft.Quantum.QsCompiler.Transformations.Core.NamespaceTransformationBase.OnSpecializationKind(QsSpecialization spec)
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildSpecializationBody(CodegenContext context, QsSpecialization sp) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 952
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildSpecialization(CodegenContext context, QsSpecialization sp) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1004
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildOperationClass@1383-2.Invoke(QsSpecialization sp) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1383
     at Microsoft.FSharp.Collections.Internal.IEnumerator.map@75.DoMoveNext(b& curr) in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 81 
     at Microsoft.FSharp.Collections.Internal.IEnumerator.MapEnumerator`1.System-Collections-IEnumerator-MoveNext() in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 68
     at Microsoft.FSharp.Collections.Internal.IEnumerator.choose@171.System-Collections-IEnumerator-MoveNext() in E:\A\_work\130\s\src\fsharp\FSharp.Core\seq.fs:line 178
     at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildOperationClass(CodegenContext globalContext, QsCallable op) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1382
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildOne@1517-8.Invoke(QsNamespaceElement _arg1) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1520
     at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x) in E:\A\_work\130\s\src\fsharp\FSharp.Core\local.fs:line 250
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildNamespace(CodegenContext globalContext, NonNullable`1 nsName, FSharpList`1 localElements) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1521
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.namespaces@1595.Invoke(Tuple`2 tupledArg) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1595
     at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x) in E:\A\_work\130\s\src\fsharp\FSharp.Core\local.fs:line 250
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.buildSyntaxTree(FSharpList`1 localElements, CodegenContext context) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1595
EXEC : error QS7109: The compilation step "CsharpGeneration" loaded from "C:/Users/samarsha/.nuget/packages/microsoft.quantum.csharpgeneration/0.11.2006.403/lib/netstandard2.1/Microsoft.Quantum.CsharpGeneration.dll" threw an exception. [C:\Users\samarsha\Desktop\Project\Project.csproj]     at Microsoft.Quantum.QsCompiler.CsharpGeneration.SimulationCode.generate(NonNullable`1 fileName, CodegenContext globalContext) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\SimulationCode.fs:line 1649
     at Microsoft.Quantum.QsCompiler.CsharpGeneration.Emitter.Microsoft-Quantum-QsCompiler-IRewriteStep-Transformation(QsCompilation compilation, QsCompilation& transformed) in D:\a\1\s\submodules\qsharp-runtime\src\Simulation\CsharpGeneration\RewriteStep.fs:line 63
     at Microsoft.Quantum.QsCompiler.RewriteSteps.LoadedStep.Transformation(QsCompilation compilation, QsCompilation& transformed)
     at Microsoft.Quantum.QsCompiler.CompilationLoader.ExecuteRewriteStep(LoadedStep rewriteStep, QsCompilation compilation, QsCompilation& transformed)


  ____________________________________________

  Q# compilation failed: 2 errors, 0 warnings
  1 logged exception

C:\Users\samarsha\.nuget\packages\microsoft.quantum.sdk\0.11.2006.403\Sdk\Sdk.targets(116,5): error MSB3073: Der Befehl "dotnet "C:\Users\samarsha\.nuget\packages\microsoft.quantum.sdk\0.11.2006.403\DefaultItems\../tools/qsc/qsc.dll" build --format MsBuild -v Detailed --response-files 
obj/qsharp/config/qsc.rsp" wurde mit dem Code -3 beendet. [C:\Users\samarsha\Desktop\Project\Project.csproj]

Fehler beim Buildvorgang.

C:/Users/samarsha/Desktop/Project/Program.qs(4,9): error QS5022: No identifier with the name "Foo" exists. [C:\Users\samarsha\Desktop\Project\Project.csproj]
EXEC : error QS7109: The compilation step "CsharpGeneration" loaded from "C:/Users/samarsha/.nuget/packages/microsoft.quantum.csharpgeneration/0.11.2006.403/lib/netstandard2.1/Microsoft.Quantum.CsharpGeneration.dll" threw an exception. [C:\Users\samarsha\Desktop\Project\Project.csproj]C:\Users\samarsha\.nuget\packages\microsoft.quantum.sdk\0.11.2006.403\Sdk\Sdk.targets(116,5): error MSB3073: Der Befehl "dotnet "C:\Users\samarsha\.nuget\packages\microsoft.quantum.sdk\0.11.2006.403\DefaultItems\../tools/qsc/qsc.dll" build --format MsBuild -v Detailed --response-files 
obj/qsharp/config/qsc.rsp" wurde mit dem Code -3 beendet. [C:\Users\samarsha\Desktop\Project\Project.csproj]
    0 Warnung(en)
    3 Fehler

Microsoft.Quantum.Sdk version: 0.11.2006.403

[bettinaheim]

Each rewrite step is supposed to be able to rely on that the syntax tree it receives is valid (which is not the case here); so the way to address this would be that the compiler does not invoke the C# generation if there are compilation errors (used to be the case, but it looks like a recent change modified that behavior).

[bettinaheim]

I'll take a look as part of this month's bug fixing session.

[bettinaheim]

Fixed with PR #473.