[AST] Add a new isDoubleType accessor to TypeBase

Author: xedin

include/swift/AST/Types.h

@@ -803,6 +803,9 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   /// Check if this is a CGFloat type from `CoreGraphics` module.
   bool isCGFloatType();
 
+  /// Check if thih sis a Double type from standard library.
+  bool isDoubleType();
+
   /// Check if this is either an Array, Set or Dictionary collection type defined
   /// at the top level of the Swift module
   bool isKnownStdlibCollectionType();

lib/AST/Type.cpp

@@ -829,6 +829,11 @@ bool TypeBase::isCGFloatType() {
          NTD->getName().is("CGFloat");
 }
 
+bool TypeBase::isDoubleType() {
+  auto *NTD = getAnyNominal();
+  return NTD ? NTD->getDecl() == getASTContext().getDoubleDecl() : false;
+}
+
 bool TypeBase::isKnownStdlibCollectionType() {
   if (auto *structType = getAs<BoundGenericStructType>()) {
     auto &ctx = getASTContext();