public override bool CheckInvocation(TexlBinding binding, TexlNode[] args, DType[] argTypes, IErrorContainer errors, out DType returnType, out Dictionary <TexlNode, DType> nodeToCoercedTypeMap)
{
Contracts.AssertValue(args);
Contracts.AssertValue(argTypes);
Contracts.Assert(args.Length == argTypes.Length);
Contracts.AssertValue(errors);
Contracts.Assert(MinArity <= args.Length && args.Length <= MaxArity);
bool isValidInvocation = base.CheckInvocation(args, argTypes, errors, out returnType, out nodeToCoercedTypeMap);
Contracts.Assert(returnType.IsTable);
if (!argTypes[0].IsTable)
{
isValidInvocation = false;
errors.EnsureError(DocumentErrorSeverity.Severe, args[0], TexlStrings.ErrNeedTable_Func, Name);
}
else
{
returnType = argTypes[0];
}
DType colsToKeep = DType.EmptyTable;
// The result type has N columns, as specified by (args[1],args[2],args[3],...)
int count = args.Length;
for (var i = 1; i < count; i++)
{
TexlNode nameArg = args[i];
DType nameArgType = argTypes[i];
// Verify we have a string literal for the column name. Accd to spec, we don't support
// arbitrary expressions that evaluate to string values, because these values contribute to
// type analysis, so they need to be known upfront (before ShowColumns executes).
StrLitNode nameNode;
if (nameArgType.Kind != DKind.String || (nameNode = nameArg.AsStrLit()) == null)
{
isValidInvocation = false;
errors.EnsureError(DocumentErrorSeverity.Severe, nameArg, TexlStrings.ErrExpectedStringLiteralArg_Name, nameArg.ToString());
continue;
}
// Verify that the name is valid.
if (!DName.IsValidDName(nameNode.Value))
{
isValidInvocation = false;
errors.EnsureError(DocumentErrorSeverity.Severe, nameArg, TexlStrings.ErrArgNotAValidIdentifier_Name, nameNode.Value);
continue;
}
DName columnName = new DName(nameNode.Value);
// Verify that the name exists.
DType columnType;
if (!returnType.TryGetType(columnName, out columnType))
{
isValidInvocation = false;
returnType.ReportNonExistingName(FieldNameKind.Logical, errors, columnName, args[i]);
continue;
}
// Verify that the name was only specified once.
DType existingColumnType;
if (colsToKeep.TryGetType(columnName, out existingColumnType))
{
isValidInvocation = false;
errors.EnsureError(DocumentErrorSeverity.Warning, nameArg, TexlStrings.WarnColumnNameSpecifiedMultipleTimes_Name, columnName);
continue;
}
// Make a note of which columns are being kept.
Contracts.Assert(columnType.IsValid);
colsToKeep = colsToKeep.Add(columnName, columnType);
}
// Drop everything but the columns that need to be kept.
returnType = colsToKeep;
return(isValidInvocation);
}