private static MethodSymbol InferExtensionMethodTypeArguments(MethodSymbol method, TypeSymbol thisType, CSharpCompilation compilation, ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
Debug.Assert(method.IsExtensionMethod);
Debug.Assert((object)thisType != null);
if (!method.IsGenericMethod || method != method.ConstructedFrom)
{
return(method);
}
// We never resolve extension methods on a dynamic receiver.
if (thisType.IsDynamic())
{
return(null);
}
var containingAssembly = method.ContainingAssembly;
var errorNamespace = containingAssembly.GlobalNamespace;
var conversions = new TypeConversions(containingAssembly.CorLibrary);
// There is absolutely no plausible syntax/tree that we could use for these
// synthesized literals. We could be speculatively binding a call to a PE method.
var syntaxTree = CSharpSyntaxTree.Dummy;
var syntax = (CSharpSyntaxNode)syntaxTree.GetRoot();
// Create an argument value for the "this" argument of specific type,
// and pass the same bad argument value for all other arguments.
var thisArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, thisType)
{
WasCompilerGenerated = true
};
var otherArgumentType = new ExtendedErrorTypeSymbol(errorNamespace, name: string.Empty, arity: 0, errorInfo: null, unreported: false);
var otherArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, otherArgumentType)
{
WasCompilerGenerated = true
};
var paramCount = method.ParameterCount;
var arguments = new BoundExpression[paramCount];
for (int i = 0; i < paramCount; i++)
{
var argument = (i == 0) ? thisArgumentValue : otherArgumentValue;
arguments[i] = argument;
}
var typeArgs = MethodTypeInferrer.InferTypeArgumentsFromFirstArgument(
conversions,
method,
arguments.AsImmutable(),
useSiteDiagnostics: ref useSiteDiagnostics);
if (typeArgs.IsDefault)
{
return(null);
}
// For the purpose of constraint checks we use error type symbol in place of type arguments that we couldn't infer from the first argument.
// This prevents constraint checking from failing for corresponding type parameters.
int firstNullInTypeArgs = -1;
var notInferredTypeParameters = PooledHashSet <TypeParameterSymbol> .GetInstance();
var typeParams = method.TypeParameters;
var typeArgsForConstraintsCheck = typeArgs;
for (int i = 0; i < typeArgsForConstraintsCheck.Length; i++)
{
if (!typeArgsForConstraintsCheck[i].HasType)
{
firstNullInTypeArgs = i;
var builder = ArrayBuilder <TypeWithAnnotations> .GetInstance();
builder.AddRange(typeArgsForConstraintsCheck, firstNullInTypeArgs);
for (; i < typeArgsForConstraintsCheck.Length; i++)
{
var typeArg = typeArgsForConstraintsCheck[i];
if (!typeArg.HasType)
{
notInferredTypeParameters.Add(typeParams[i]);
builder.Add(TypeWithAnnotations.Create(ErrorTypeSymbol.UnknownResultType));
}
else
{
builder.Add(typeArg);
}
}
typeArgsForConstraintsCheck = builder.ToImmutableAndFree();
break;
}
}
// Check constraints.
var diagnosticsBuilder = ArrayBuilder <TypeParameterDiagnosticInfo> .GetInstance();
var substitution = new TypeMap(typeParams, typeArgsForConstraintsCheck);
ArrayBuilder <TypeParameterDiagnosticInfo> useSiteDiagnosticsBuilder = null;
var success = method.CheckConstraints(conversions, substitution, typeParams, typeArgsForConstraintsCheck, compilation, diagnosticsBuilder, nullabilityDiagnosticsBuilderOpt: null, ref useSiteDiagnosticsBuilder,
ignoreTypeConstraintsDependentOnTypeParametersOpt: notInferredTypeParameters.Count > 0 ? notInferredTypeParameters : null);
diagnosticsBuilder.Free();
notInferredTypeParameters.Free();
if (useSiteDiagnosticsBuilder != null && useSiteDiagnosticsBuilder.Count > 0)
{
if (useSiteDiagnostics == null)
{
useSiteDiagnostics = new HashSet <DiagnosticInfo>();
}
foreach (var diag in useSiteDiagnosticsBuilder)
{
useSiteDiagnostics.Add(diag.DiagnosticInfo);
}
}
if (!success)
{
return(null);
}
// For the purpose of construction we use original type parameters in place of type arguments that we couldn't infer from the first argument.
ImmutableArray <TypeWithAnnotations> typeArgsForConstruct = typeArgs;
if (typeArgs.Any(t => !t.HasType))
{
typeArgsForConstruct = typeArgs.ZipAsArray(
method.TypeParameters,
(t, tp) => t.HasType ? t : TypeWithAnnotations.Create(tp));
}
return(method.Construct(typeArgsForConstruct));
}
/// <summary>
/// This method implements the algorithm in spec section 7.6.5.1.
///
/// For method group conversions, there are situations in which the conversion is
/// considered to exist ("Otherwise the algorithm produces a single best method M having
/// the same number of parameters as D and the conversion is considered to exist"), but
/// application of the conversion fails. These are the "final validation" steps of
/// overload resolution.
/// </summary>
/// <returns>
/// True if there is any error.
/// </returns>
private bool MemberGroupFinalValidation(BoundExpression receiverOpt, MethodSymbol methodSymbol, CSharpSyntaxNode node, DiagnosticBag diagnostics, bool invokedAsExtensionMethod)
{
if (MemberGroupFinalValidationAccessibilityChecks(receiverOpt, methodSymbol, node, diagnostics, invokedAsExtensionMethod))
{
return true;
}
// SPEC: If the best method is a generic method, the type arguments (supplied or inferred) are checked against the constraints
// SPEC: declared on the generic method. If any type argument does not satisfy the corresponding constraint(s) on
// SPEC: the type parameter, a binding-time error occurs.
// The portion of the overload resolution spec quoted above is subtle and somewhat
// controversial. The upshot of this is that overload resolution does not consider
// constraints to be a part of the signature. Overload resolution matches arguments to
// parameter lists; it does not consider things which are outside of the parameter list.
// If the best match from the arguments to the formal parameters is not viable then we
// give an error rather than falling back to a worse match.
//
// Consider the following:
//
// void M<T>(T t) where T : Reptile {}
// void M(object x) {}
// ...
// M(new Giraffe());
//
// The correct analysis is to determine that the applicable candidates are
// M<Giraffe>(Giraffe) and M(object). Overload resolution then chooses the former
// because it is an exact match, over the latter which is an inexact match. Only after
// the best method is determined do we check the constraints and discover that the
// constraint on T has been violated.
//
// Note that this is different from the rule that says that during type inference, if an
// inference violates a constraint then inference fails. For example:
//
// class C<T> where T : struct {}
// ...
// void M<U>(U u, C<U> c){}
// void M(object x, object y) {}
// ...
// M("hello", null);
//
// Type inference determines that U is string, but since C<string> is not a valid type
// because of the constraint, type inference fails. M<string> is never added to the
// applicable candidate set, so the applicable candidate set consists solely of
// M(object, object) and is therefore the best match.
return !methodSymbol.CheckConstraints(this.Conversions, node, this.Compilation, diagnostics);
}
/// <summary>
/// If the extension method is applicable based on the "this" argument type, return
/// the method constructed with the inferred type arguments. If the method is not an
/// unconstructed generic method, type inference is skipped. If the method is not
/// applicable, or if constraints when inferring type parameters from the "this" type
/// are not satisfied, the return value is null.
/// </summary>
public static MethodSymbol InferExtensionMethodTypeArguments(this MethodSymbol method, TypeSymbol thisType, Compilation compilation, ref HashSet <DiagnosticInfo> useSiteDiagnostics)
{
Debug.Assert(method.IsExtensionMethod);
Debug.Assert((object)thisType != null);
if (!method.IsGenericMethod || method != method.ConstructedFrom)
{
return(method);
}
// We never resolve extension methods on a dynamic receiver.
if (thisType.IsDynamic())
{
return(null);
}
var containingAssembly = method.ContainingAssembly;
var errorNamespace = containingAssembly.GlobalNamespace;
var conversions = new TypeConversions(containingAssembly.CorLibrary);
// There is absolutely no plausible syntax/tree that we could use for these
// synthesized literals. We could be speculatively binding a call to a PE method.
var syntaxTree = CSharpSyntaxTree.Dummy;
var syntax = (CSharpSyntaxNode)syntaxTree.GetRoot();
// Create an argument value for the "this" argument of specific type,
// and pass the same bad argument value for all other arguments.
var thisArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, thisType)
{
WasCompilerGenerated = true
};
var otherArgumentType = new ExtendedErrorTypeSymbol(errorNamespace, name: string.Empty, arity: 0, errorInfo: null, unreported: false);
var otherArgumentValue = new BoundLiteral(syntax, ConstantValue.Bad, otherArgumentType)
{
WasCompilerGenerated = true
};
var paramCount = method.ParameterCount;
var arguments = new BoundExpression[paramCount];
var argumentTypes = new TypeSymbol[paramCount];
for (int i = 0; i < paramCount; i++)
{
var argument = (i == 0) ? thisArgumentValue : otherArgumentValue;
arguments[i] = argument;
argumentTypes[i] = argument.Type;
}
var typeArgs = MethodTypeInferrer.InferTypeArgumentsFromFirstArgument(
conversions,
method,
argumentTypes.AsImmutableOrNull(),
arguments.AsImmutableOrNull(),
ref useSiteDiagnostics);
if (typeArgs.IsDefault)
{
return(null);
}
// Check constraints.
var diagnosticsBuilder = ArrayBuilder <TypeParameterDiagnosticInfo> .GetInstance();
var typeParams = method.TypeParameters;
var substitution = new TypeMap(typeParams, typeArgs);
ArrayBuilder <TypeParameterDiagnosticInfo> useSiteDiagnosticsBuilder = null;
var success = method.CheckConstraints(conversions, substitution, method.TypeParameters, typeArgs, compilation, diagnosticsBuilder, ref useSiteDiagnosticsBuilder);
diagnosticsBuilder.Free();
if (useSiteDiagnosticsBuilder != null && useSiteDiagnosticsBuilder.Count > 0)
{
if (useSiteDiagnostics == null)
{
useSiteDiagnostics = new HashSet <DiagnosticInfo>();
}
foreach (var diag in useSiteDiagnosticsBuilder)
{
useSiteDiagnostics.Add(diag.DiagnosticInfo);
}
}
if (!success)
{
return(null);
}
return(method.Construct(typeArgs));
}
