/// <summary>
/// Given an operation, goes through all decendent operations and returns true if the symbol passed in
/// is ever assigned a possibly null value as determined by nullable flow state. Returns
/// null if no references are found, letting the caller determine what to do with that information
/// </summary>
public static bool?IsSymbolAssignedPossiblyNullValue(SemanticModel semanticModel, IOperation operation, ISymbol symbol)
{
var references = operation.DescendantsAndSelf()
.Where(o => IsSymbolReferencedByOperation(o, symbol));
var hasReference = false;
foreach (var reference in references)
{
hasReference = true;
// foreach statements are handled special because the iterator is not assignable, so the elementtype
// annotation is accurate for determining if the loop declaration has a reference that allows the symbol
// to be null
if (reference is IForEachLoopOperation forEachLoop)
{
var foreachInfo = semanticModel.GetForEachStatementInfo((CommonForEachStatementSyntax)forEachLoop.Syntax);
if (foreachInfo.ElementType is null)
{
continue;
}
// Use NotAnnotated here to keep both Annotated and None (oblivious) treated the same, since
// this is directly looking at the annotation and not the flow state
if (foreachInfo.ElementType.NullableAnnotation != NullableAnnotation.NotAnnotated)
{
return(true);
}
continue;
}
var syntax = reference is IVariableDeclaratorOperation variableDeclarator
? variableDeclarator.GetVariableInitializer() !.Value.Syntax
: reference.Syntax;
var typeInfo = semanticModel.GetTypeInfo(syntax);
if (typeInfo.Nullability.FlowState == NullableFlowState.MaybeNull)
{
return(true);
}
}
return(hasReference ? (bool?)false : null);
}