/// <summary>
/// If the given property is a reference type and is not initialized, it should *either* be marked as nullable or
/// be initialized to a non-null value. This method will do it's best to initialize the property using a default constructor
/// or empty string, and failing that will mark the type as nullable.
/// </summary>
/// <param name="property">The <see cref="PropertyDeclarationSyntax"/> to update. Must be on a <see cref="SyntaxTree"/>.</param>
/// <param name="semanticModel"><see cref="SemanticModel"/> used to perform type analysis.</param>
/// <returns>The mutated property declaration, or the original if no mutation was required.</returns>
public static PropertyDeclarationSyntax MakeNullableOrInitializeIfReferenceType(this PropertyDeclarationSyntax property,
SemanticModel semanticModel)
{
if (property == null)
{
throw new ArgumentNullException(nameof(property));
}
if (semanticModel == null)
{
throw new ArgumentNullException(nameof(semanticModel));
}
if (property.Initializer != null || property.ExpressionBody != null)
{
// No need if already initialized or expression body only
return(property);
}
if (property.Type is NullableTypeSyntax)
{
// Already nullable
return(property);
}
var typeInfo = semanticModel.GetTypeInfo(property.Type);
if (typeInfo.Type?.IsReferenceType ?? false)
{
if (typeInfo.Type.SpecialType == SpecialType.System_String)
{
// Initialize to an empty string
property = property
.WithInitializer(EqualsValueClause(SyntaxHelpers.StringLiteral("")));
}
else if (!typeInfo.Type.IsAbstract && typeInfo.Type.GetMembers()
.Where(p => p.Kind == SymbolKind.Method && p.Name == ".ctor")
.Cast <IMethodSymbol>()
.Any(p => p.Parameters.Length == 0 && p.DeclaredAccessibility == Accessibility.Public))
{
// Build a default object using the default constructor
property = property
.WithInitializer(EqualsValueClause(ObjectCreationExpression(property.Type)));
}
else
{
// Mark the types as nullable, even if the parameter is required
// This will encourage SDK consumers to check for nulls and prevent NREs
property = property.MakeNullable();
}
}
return(property);
}
public static StatementSyntax ThrowIfArgumentNull(string parameterName) =>
IfNull(
IdentifierName(parameterName),
Block(ThrowStatement(
ObjectCreationExpression(WellKnownTypes.System.ArgumentNullException.Name)
.AddArgumentListArguments(Argument(SyntaxHelpers.StringLiteral(parameterName))))));
public static ExpressionSyntax ArgumentOrThrowIfNull(string parameterName) =>
BinaryExpression(SyntaxKind.CoalesceExpression,
IdentifierName(parameterName),
ThrowExpression(
ObjectCreationExpression(WellKnownTypes.System.ArgumentNullException.Name)
.AddArgumentListArguments(Argument(SyntaxHelpers.StringLiteral(parameterName)))));