internal static bool ReportDefaultParameterErrors(
Binder binder,
Symbol owner,
ParameterSyntax parameterSyntax,
SourceParameterSymbol parameter,
BoundExpression defaultExpression,
BoundExpression convertedExpression,
DiagnosticBag diagnostics)
{
bool hasErrors = false;
// SPEC VIOLATION: The spec says that the conversion from the initializer to the
// parameter type is required to be either an identity or a nullable conversion, but
// that is not right:
//
// void M(short myShort = 10) {}
// * not an identity or nullable conversion but should be legal
//
// void M(object obj = (dynamic)null) {}
// * an identity conversion, but should be illegal
//
// void M(MyStruct? myStruct = default(MyStruct)) {}
// * a nullable conversion, but must be illegal because we cannot generate metadata for it
//
// Even if the expression is thoroughly illegal, we still want to bind it and
// stick it in the parameter because we want to be able to analyze it for
// IntelliSense purposes.
TypeSymbol parameterType = parameter.Type;
HashSet <DiagnosticInfo> useSiteDiagnostics = null;
Conversion conversion = binder.Conversions.ClassifyImplicitConversionFromExpression(defaultExpression, parameterType, ref useSiteDiagnostics);
diagnostics.Add(defaultExpression.Syntax, useSiteDiagnostics);
var refKind = GetModifiers(parameterSyntax.Modifiers, out SyntaxToken refnessKeyword, out SyntaxToken paramsKeyword, out SyntaxToken thisKeyword);
// CONSIDER: We are inconsistent here regarding where the error is reported; is it
// CONSIDER: reported on the parameter name, or on the value of the initializer?
// CONSIDER: Consider making this consistent.
if (refKind == RefKind.Ref || refKind == RefKind.Out)
{
// error CS1741: A ref or out parameter cannot have a default value
diagnostics.Add(ErrorCode.ERR_RefOutDefaultValue, refnessKeyword.GetLocation());
hasErrors = true;
}
else if (paramsKeyword.Kind() == SyntaxKind.ParamsKeyword)
{
// error CS1751: Cannot specify a default value for a parameter array
diagnostics.Add(ErrorCode.ERR_DefaultValueForParamsParameter, paramsKeyword.GetLocation());
hasErrors = true;
}
else if (thisKeyword.Kind() == SyntaxKind.ThisKeyword)
{
// Only need to report CS1743 for the first parameter. The caller will
// have reported CS1100 if 'this' appeared on another parameter.
if (parameter.Ordinal == 0)
{
// error CS1743: Cannot specify a default value for the 'this' parameter
diagnostics.Add(ErrorCode.ERR_DefaultValueForExtensionParameter, thisKeyword.GetLocation());
hasErrors = true;
}
}
else if (!defaultExpression.HasAnyErrors && !IsValidDefaultValue(defaultExpression.IsTypelessNew() ? convertedExpression : defaultExpression))
{
// error CS1736: Default parameter value for '{0}' must be a compile-time constant
diagnostics.Add(ErrorCode.ERR_DefaultValueMustBeConstant, parameterSyntax.Default.Value.Location, parameterSyntax.Identifier.ValueText);
hasErrors = true;
}
else if (!conversion.Exists ||
conversion.IsUserDefined ||
conversion.IsIdentity && parameterType.SpecialType == SpecialType.System_Object && defaultExpression.Type.IsDynamic())
{
// If we had no implicit conversion, or a user-defined conversion, report an error.
//
// Even though "object x = (dynamic)null" is a legal identity conversion, we do not allow it.
// CONSIDER: We could. Doesn't hurt anything.
// error CS1750: A value of type '{0}' cannot be used as a default parameter because there are no standard conversions to type '{1}'
diagnostics.Add(ErrorCode.ERR_NoConversionForDefaultParam, parameterSyntax.Identifier.GetLocation(),
defaultExpression.Display, parameterType);
hasErrors = true;
}
else if (conversion.IsReference &&
(parameterType.SpecialType == SpecialType.System_Object || parameterType.Kind == SymbolKind.DynamicType) &&
(object)defaultExpression.Type != null &&
defaultExpression.Type.SpecialType == SpecialType.System_String ||
conversion.IsBoxing)
{
// We don't allow object x = "hello", object x = 123, dynamic x = "hello", etc.
// error CS1763: '{0}' is of type '{1}'. A default parameter value of a reference type other than string can only be initialized with null
diagnostics.Add(ErrorCode.ERR_NotNullRefDefaultParameter, parameterSyntax.Identifier.GetLocation(),
parameterSyntax.Identifier.ValueText, parameterType);
hasErrors = true;
}
else if (conversion.IsNullable && !defaultExpression.Type.IsNullableType() &&
!(parameterType.GetNullableUnderlyingType().IsEnumType() || parameterType.GetNullableUnderlyingType().IsIntrinsicType()))
{
// We can do:
// M(int? x = default(int))
// M(int? x = default(int?))
// M(MyEnum? e = default(enum))
// M(MyEnum? e = default(enum?))
// M(MyStruct? s = default(MyStruct?))
//
// but we cannot do:
//
// M(MyStruct? s = default(MyStruct))
// error CS1770:
// A value of type '{0}' cannot be used as default parameter for nullable parameter '{1}' because '{0}' is not a simple type
diagnostics.Add(ErrorCode.ERR_NoConversionForNubDefaultParam, parameterSyntax.Identifier.GetLocation(),
defaultExpression.Type, parameterSyntax.Identifier.ValueText);
hasErrors = true;
}
// Certain contexts allow default parameter values syntactically but they are ignored during
// semantic analysis. They are:
// 1. Explicitly implemented interface methods; since the method will always be called
// via the interface, the defaults declared on the implementation will not
// be seen at the call site.
//
// UNDONE: 2. The "actual" side of a partial method; the default values are taken from the
// UNDONE: "declaring" side of the method.
//
// UNDONE: 3. An indexer with only one formal parameter; it is illegal to omit every argument
// UNDONE: to an indexer.
//
// 4. A user-defined operator; it is syntactically impossible to omit the argument.
if (owner.IsExplicitInterfaceImplementation() ||
owner.IsPartialImplementation() ||
owner.IsOperator())
{
// CS1066: The default value specified for parameter '{0}' will have no effect because it applies to a
// member that is used in contexts that do not allow optional arguments
diagnostics.Add(ErrorCode.WRN_DefaultValueForUnconsumedLocation,
parameterSyntax.Identifier.GetLocation(),
parameterSyntax.Identifier.ValueText);
}
return(hasErrors);
}
