Fix AD0001: NRE in SE for declaration pattern

[pavel-mikula-sonarsource]

As reported here and observed inside ascx.cs file:

CSC : error AD0001: Analyzer 'SonarAnalyzer.Rules.CSharp.SymbolicExecutionRunner' threw an exception of type 'SonarAnalyzer.SymbolicExecution.SymbolicExecutionException' with message 'Error processing method: collectiveResultRepeater_ItemDataBound
 Inner exception: System.NullReferenceException: Object reference not set to an instance of an object.
     at SonarAnalyzer.Helpers.TypeHelper.<>c__DisplayClass20_0.<Implements>b__0(INamedTypeSymbol x)
     at System.Linq.ImmutableArrayExtensions.Any[T](ImmutableArray`1 immutableArray, Func`2 predicate)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationProcessors.IsPattern.BoolConstraintFromDeclarationPattern(ObjectConstraint valueConstraint, IDeclarationPatternOperationWrapper declaration)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationProcessors.IsPattern.BoolConstraintFromPattern(ProgramState state, SymbolicValue value, IPatternOperationWrapper pattern)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationProcessors.IsPattern.BoolConstraintFromOperation(ProgramState state, IIsPatternOperationWrapper operation, Boolean isLoopCondition, Int32 visitCount)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationProcessors.BranchingProcessor`1.Process(SymbolicContext context, T operation)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationProcessors.MultiProcessor`1.Process(SymbolicContext context)
     at SonarAnalyzer.SymbolicExecution.Roslyn.OperationDispatcher.Process(SymbolicContext context)
     at SonarAnalyzer.SymbolicExecution.Roslyn.RoslynSymbolicExecution.<ProcessOperation>d__17.MoveNext()
     at SonarAnalyzer.SymbolicExecution.Roslyn.RoslynSymbolicExecution.Execute()
     at SonarAnalyzer.Rules.SymbolicExecutionRunnerBase.AnalyzeRoslyn(SonarAnalysisContext analysisContext, SonarSyntaxNodeReportingContext nodeContext, ISymbol symbol)'. 

We don't have a reproducer (yet).

[zsolt-kolbay-sonarsource]

The only place where this can happen is this line, if declaration.InputType is null. Then, the null value ends up in the extension methods where an NRE is thrown.
I couldn't yet replicate it. I tried with using object, dynamic or generic types in declaration patterns.

[Tim-Pohlmann]

The user shared the code. It looks harmless:

var collectiveEmployee = e.Item.DataItem as CollectiveBaseDto;
...
if (collectiveEmployee is CollectiveEmployeeEpldto CollectiveEPLDTOEmp)

Do you know where the call to .Any comes from in the stack trace?

[pavel-mikula-sonarsource]

In case InputType is null, then InputType.DerivesOrImplements returns false , because it's null-tolerant everywhere.

[Tim-Pohlmann]

I looked again at the stack trace: It is this line:

    private static bool Implements(this ITypeSymbol typeSymbol, ISymbol type) =>
        typeSymbol is { }
        && typeSymbol.AllInterfaces.Any(x => type.IsDefinition ? x.OriginalDefinition.Equals(type) : x.Equals(type));

It can throw an NRE if type, x or x.OriginalDefinition are null.

• type is null if declaration.NarrowedType is null.
• x is null if typeSymbol.AllInterfaces contains a null reference (probably not possible?).
• Can x.OriginalDefinition be null?

The first one seems the most likely to me, but I'm not sure.

[pavel-mikula-sonarsource]

This makes sense.

• type is null if declaration.NarrowedType is null.

AllInterfaces returns ImmutableArray that is a struct and cannot be null
OriginalDefinition cannot be null, it defaults to this.

[mary-georgiou-sonarsource]

I tried with VSBuild Tools 2019 and 2022.
I could not reproduce it.