[ModuleInterface] Allow falling back to prefer TypeReprs

There are still cases (a module with a type that's the same name as the
module) where we cannot fully qualify all types. In those cases, allow
them to remain unqualified with a flag, `-Xfrontend
-preserve-types-as-written-in-module-interface`.

Author: Harlan Haskins

include/swift/AST/PrintOptions.h

@@ -494,7 +494,7 @@ struct PrintOptions {
   /// consistent and well-formed.
   ///
   /// \see swift::emitParseableInterface
-  static PrintOptions printParseableInterfaceFile();
+  static PrintOptions printParseableInterfaceFile(bool preferTypeRepr);
 
   static PrintOptions printModuleInterface();
   static PrintOptions printTypeInterface(Type T);

include/swift/Frontend/ParseableInterfaceSupport.h

@@ -27,6 +27,10 @@ class ModuleDecl;
 
 /// Options for controlling the generation of the .swiftinterface output.
 struct ParseableInterfaceOptions {
+  /// Should we prefer printing TypeReprs when writing out types in a module
+  /// interface, or should we fully-qualify them?
+  bool PreserveTypesAsWrittenInModuleInterface = false;
+
   /// Copy of all the command-line flags passed at .swiftinterface
   /// generation time, re-applied to CompilerInvocation when reading
   /// back .swiftinterface and reconstructing .swiftmodule.

include/swift/Option/FrontendOptions.td

@@ -535,6 +535,11 @@ def build_module_from_parseable_interface :
   Alias<compile_module_from_interface>,
   ModeOpt;
 
+def preserve_types_as_written_in_module_interface :
+  Flag<["-"], "preserve-types-as-written-in-module-interface">,
+  HelpText<"When emitting a module interface, preserve the types as they were "
+           "written in the source, rather than fully-qualifying them.">;
+
 def prebuilt_module_cache_path :
   Separate<["-"], "prebuilt-module-cache-path">,
   HelpText<"Directory of prebuilt modules for loading module interfaces">;

lib/AST/ASTPrinter.cpp

@@ -94,7 +94,7 @@ static bool contributesToParentTypeStorage(const AbstractStorageDecl *ASD) {
   return !ND->isResilient() && ASD->hasStorage() && !ASD->isStatic();
 }
 
-PrintOptions PrintOptions::printParseableInterfaceFile() {
+PrintOptions PrintOptions::printParseableInterfaceFile(bool preferTypeRepr) {
   PrintOptions result;
   result.PrintLongAttrsOnSeparateLines = true;
   result.TypeDefinitions = true;
@@ -110,7 +110,7 @@ PrintOptions PrintOptions::printParseableInterfaceFile() {
   result.EnumRawValues = EnumRawValueMode::PrintObjCOnly;
   result.OpaqueReturnTypePrinting =
       OpaqueReturnTypePrintingMode::StableReference;
-  result.PreferTypeRepr = false;
+  result.PreferTypeRepr = preferTypeRepr;
 
   // We should print __consuming, __owned, etc for the module interface file.
   result.SkipUnderscoredKeywords = false;

lib/Frontend/CompilerInvocation.cpp

@@ -197,6 +197,14 @@ static void PrintArg(raw_ostream &OS, const char *Arg, StringRef TempDir) {
   OS << '"';
 }
 
+static void ParseParseableInterfaceArgs(ParseableInterfaceOptions &Opts,
+                                        ArgList &Args) {
+  using namespace options;
+
+  Opts.PreserveTypesAsWrittenInModuleInterface |=
+    Args.hasArg(OPT_preserve_types_as_written_in_module_interface);
+}
+
 /// Save a copy of any flags marked as ModuleInterfaceOption, if running
 /// in a mode that is going to emit a .swiftinterface file.
 static void SaveParseableInterfaceArgs(ParseableInterfaceOptions &Opts,
@@ -1305,6 +1313,7 @@ bool CompilerInvocation::parseArgs(
     return true;
   }
 
+  ParseParseableInterfaceArgs(ParseableInterfaceOpts, ParsedArgs);
   SaveParseableInterfaceArgs(ParseableInterfaceOpts, FrontendOpts,
                              ParsedArgs, Diags);
 

lib/Frontend/ParseableInterfaceSupport.cpp

@@ -411,7 +411,8 @@ bool swift::emitParseableInterface(raw_ostream &out,
   printToolVersionAndFlagsComment(out, Opts, M);
   printImports(out, M);
 
-  const PrintOptions printOptions = PrintOptions::printParseableInterfaceFile();
+  const PrintOptions printOptions = PrintOptions::printParseableInterfaceFile(
+      Opts.PreserveTypesAsWrittenInModuleInterface);
   InheritedProtocolCollector::PerTypeMap inheritedProtocolMap;
 
   SmallVector<Decl *, 16> topLevelDecls;

test/ParseableInterface/preserve-type-repr.swift

@@ -0,0 +1,34 @@
+// RUN: %target-swift-frontend -typecheck -emit-module-interface-path - %s -enable-library-evolution -module-name PreferTypeRepr -preserve-types-as-written-in-module-interface | %FileCheck %s --check-prefix PREFER
+// RUN: %target-swift-frontend -typecheck -emit-module-interface-path - %s -enable-library-evolution -module-name PreferTypeRepr | %FileCheck %s --check-prefix DONTPREFER
+
+public protocol Pet {}
+
+// PREFER: public struct Parrot : Pet {
+// DONTPREFER: public struct Parrot : PreferTypeRepr.Pet {
+// CHECK-NEXT: }
+public struct Parrot: Pet {}
+
+// CHECK: public struct Ex<T> where T : PreferTypeRepr.Pet {
+public struct Ex<T: Pet> {
+  // PREFER: public var hasCeasedToBe: Bool {
+  // DONTPREFER: public var hasCeasedToBe: Swift.Bool {
+  // CHECK: get
+  // CHECK-NEXT: }
+  public var hasCeasedToBe: Bool { false }
+
+// CHECK-NEXT: }
+}
+
+// CHECK: public struct My<T> {
+// CHECK-NEXT: }
+public struct My<T> {}
+
+// CHECK: extension My where T : PreserveTypeRepr.Pet
+extension My where T: Pet {
+  // CHECK: public func isPushingUpDaisies() -> Swift.String
+  public func isPushingUpDaisies() -> String { "" }
+}
+
+// PREFER: public func isNoMore(_ pet: Ex<Parrot>) -> Bool
+// DONTPREFER: public func isNoMore(_ pet: PreferTypeRepr.Ex<PreferTypeRepr.Parrot>) -> Swift.Bool
+public func isNoMore(_ pet: Ex<Parrot>) -> Bool {}