[NFC] Abstracting isStdlibType and isStdLibDecl logic into Type and Decl

include/swift/AST/Decl.h

@@ -882,6 +882,9 @@ class alignas(1 << DeclAlignInBits) Decl {
   bool hasUnderscoredNaming() const;
 
   bool isPrivateStdlibDecl(bool treatNonBuiltinProtocolsAsPublic = true) const;
+
+  /// Check if this is a declaration defined at the top level of the Swift module
+  bool isStdlibDecl() const;
 
   AvailabilityContext getAvailabilityForLinkage() const;
 

include/swift/AST/Types.h

@@ -780,6 +780,9 @@ class alignas(1 << TypeAlignInBits) TypeBase {
 
   /// Check if this type is equal to Builtin.IntN.
   bool isBuiltinIntegerType(unsigned bitWidth);
+
+  /// Check if this is a nominal type defined at the top level of the Swift module
+  bool isStdlibType();
 
   /// If this is a class type or a bound generic class type, returns the
   /// (possibly generic) class.

lib/AST/ASTMangler.cpp

@@ -753,11 +753,6 @@ static const char *getMetatypeRepresentationOp(MetatypeRepresentation Rep) {
   llvm_unreachable("Unhandled MetatypeRepresentation in switch.");
 }
 
-static bool isStdlibType(const TypeDecl *decl) {
-  DeclContext *dc = decl->getDeclContext();
-  return dc->isModuleScopeContext() && dc->getParentModule()->isStdlibModule();
-}
-
 /// Whether to mangle the given type as generic.
 static bool shouldMangleAsGeneric(Type type) {
   if (!type)
@@ -986,7 +981,7 @@ void ASTMangler::appendType(Type type, const ValueDecl *forDecl) {
         if (tryMangleTypeSubstitution(tybase))
           return;
 
-        if (isStdlibType(Decl) && Decl->getName().str() == "Optional") {
+        if (Decl->isStdlibDecl() && Decl->getName().str() == "Optional") {
           auto GenArgs = type->castTo<BoundGenericType>()->getGenericArgs();
           assert(GenArgs.size() == 1);
           appendType(GenArgs[0], forDecl);
@@ -2483,7 +2478,7 @@ void ASTMangler::appendDeclType(const ValueDecl *decl, bool isFunctionMangling)
 
 bool ASTMangler::tryAppendStandardSubstitution(const GenericTypeDecl *decl) {
   // Bail out if our parent isn't the swift standard library.
-  if (!isStdlibType(decl))
+  if (!decl->isStdlibDecl())
     return false;
 
   if (isa<NominalTypeDecl>(decl)) {

lib/AST/Decl.cpp

@@ -788,6 +788,12 @@ bool Decl::isPrivateStdlibDecl(bool treatNonBuiltinProtocolsAsPublic) const {
   return hasUnderscoredNaming();
 }
 
+bool Decl::isStdlibDecl() const {
+  DeclContext *DC = getDeclContext();
+  return DC->isModuleScopeContext() &&
+         DC->getParentModule()->isStdlibModule();
+}
+
 AvailabilityContext Decl::getAvailabilityForLinkage() const {
   auto containingContext =
       AvailabilityInference::annotatedAvailableRange(this, getASTContext());

lib/AST/Type.cpp

@@ -751,6 +751,15 @@ bool TypeBase::isExistentialWithError() {
   return layout.isExistentialWithError(getASTContext());
 }
 
+bool TypeBase::isStdlibType() {
+  if (auto *NTD = getAnyNominal()) {
+    auto *DC = NTD->getDeclContext();
+    return DC->isModuleScopeContext() &&
+           DC->getParentModule()->isStdlibModule();
+  }
+  return false;
+}
+
 /// Remove argument labels from the function type.
 Type TypeBase::removeArgumentLabels(unsigned numArgumentLabels) {
   // If there is nothing to remove, don't.

lib/Sema/CSDiagnostics.cpp

@@ -515,18 +515,8 @@ bool MissingConformanceFailure::diagnoseAsAmbiguousOperatorRef() {
   if (!ODRE)
     return false;
 
-  auto isStdlibType = [](Type type) {
-    if (auto *NTD = type->getAnyNominal()) {
-      auto *DC = NTD->getDeclContext();
-      return DC->isModuleScopeContext() &&
-             DC->getParentModule()->isStdlibModule();
-    }
-
-    return false;
-  };
-
   auto name = ODRE->getDecls().front()->getBaseName();
-  if (!(name.isOperator() && isStdlibType(getLHS()) && isStdlibType(getRHS())))
+  if (!(name.isOperator() && getLHS()->isStdlibType() && getRHS()->isStdlibType()))
     return false;
 
   // If this is an operator reference and both types are from stdlib,

lib/Sema/CSSimplify.cpp

@@ -1330,16 +1330,7 @@ assessRequirementFailureImpact(ConstraintSystem &cs, Type requirementType,
   if (!anchor)
     return 1;
 
-  auto isStdlibType = [&](Type type) {
-    if (auto *NTD = type->getAnyNominal()) {
-      auto *DC = NTD->getDeclContext();
-      return DC->isModuleScopeContext() &&
-             DC->getParentModule()->isStdlibModule();
-    }
-    return false;
-  };
-
-  if (requirementType && isStdlibType(cs.simplifyType(requirementType))) {
+  if (requirementType && cs.simplifyType(requirementType)->isStdlibType()) {
     if (auto last = locator.last()) {
       if (auto requirement = last->getAs<LocatorPathElt::AnyRequirement>()) {
         auto kind = requirement->getRequirementKind();