[AST] Introduce ASTMangler::forUSR

Rather than setting the USR-specific bits for each USR entrypoint
into the mangler just expose a convenience constructor for USR
generation that sets them.

Author: hamishknight

include/swift/AST/ASTMangler.h

@@ -198,6 +198,12 @@ class ASTMangler : public Mangler {
                  : ManglingFlavor::Default;
   }
 
+  /// Create an ASTMangler suitable for mangling a USR for use in semantic
+  /// functionality.
+  static ASTMangler forUSR(const ASTContext &Ctx) {
+    return ASTMangler(Ctx, /*DWARFMangling*/ true);
+  }
+
   const ASTContext &getASTContext() { return Context; }
 
   void addTypeSubstitution(Type type, GenericSignature sig) {

lib/AST/ASTMangler.cpp

@@ -958,8 +958,6 @@ std::string ASTMangler::mangleTypeAsContextUSR(const NominalTypeDecl *type) {
 }
 
 std::string ASTMangler::mangleTypeAsUSR(Type Ty) {
-  DWARFMangling = true;
-  RespectOriginallyDefinedIn = false;
   beginMangling();
 
   Ty = getTypeForDWARFMangling(Ty);
@@ -1019,8 +1017,6 @@ ASTMangler::mangleAnyDecl(const ValueDecl *Decl,
 
 std::string ASTMangler::mangleDeclAsUSR(const ValueDecl *Decl,
                                         StringRef USRPrefix) {
-  llvm::SaveAndRestore<bool> respectOriginallyDefinedInRAII(
-      RespectOriginallyDefinedIn, false);
   return (llvm::Twine(USRPrefix) + mangleAnyDecl(Decl, false)).str();
 }
 
@@ -1029,8 +1025,6 @@ std::string ASTMangler::mangleAccessorEntityAsUSR(AccessorKind kind,
                                                   StringRef USRPrefix,
                                                   bool isStatic) {
   beginManglingWithoutPrefix();
-  llvm::SaveAndRestore<bool> respectOriginallyDefinedInRAII(
-      RespectOriginallyDefinedIn, false);
   llvm::SaveAndRestore<bool> allowUnnamedRAII(AllowNamelessEntities, true);
   Buffer << USRPrefix;
   appendAccessorEntity(getCodeForAccessorKind(kind), decl, isStatic);

lib/AST/USRGeneration.cpp

@@ -40,7 +40,8 @@ static inline StringRef getUSRSpacePrefix() {
 bool ide::printTypeUSR(Type Ty, raw_ostream &OS) {
   assert(!Ty->hasArchetype() && "cannot have contextless archetypes mangled.");
   Ty = Ty->getCanonicalType()->getRValueType();
-  Mangle::ASTMangler Mangler(Ty->getASTContext());
+  using namespace Mangle;
+  ASTMangler Mangler = ASTMangler::forUSR(Ty->getASTContext());
   OS << Mangler.mangleTypeAsUSR(Ty);
   return false;
 }
@@ -245,7 +246,8 @@ swift::SwiftUSRGenerationRequest::evaluate(Evaluator &evaluator,
   if (declIFaceTy.findIf([](Type t) -> bool { return t->is<ModuleType>(); }))
     return std::string();
 
-  Mangle::ASTMangler NewMangler(D->getASTContext());
+  using namespace Mangle;
+  ASTMangler NewMangler = ASTMangler::forUSR(D->getASTContext());
   return NewMangler.mangleDeclAsUSR(D, getUSRSpacePrefix());
 }
 
@@ -375,7 +377,8 @@ bool ide::printAccessorUSR(const AbstractStorageDecl *D, AccessorKind AccKind,
     return printObjCUSRForAccessor(SD, AccKind, OS);
   }
 
-  Mangle::ASTMangler NewMangler(D->getASTContext());
+  using namespace Mangle;
+  ASTMangler NewMangler = ASTMangler::forUSR(D->getASTContext());
   std::string Mangled = NewMangler.mangleAccessorEntityAsUSR(AccKind,
                           SD, getUSRSpacePrefix(), SD->isStatic());