Allow one to separately specify the ABI name of a module.

Introduce a new compiler flag `-module-abi-name <name>` that uses the
given name as the ABI name for the module (rather than the module's
name in source code). The ABI name impacts name mangling and metadata.

Author: DougGregor

include/swift/AST/Module.h

@@ -166,6 +166,9 @@ class ModuleDecl : public DeclContext, public TypeDecl {
   friend class DirectOperatorLookupRequest;
   friend class DirectPrecedenceGroupLookupRequest;
 
+  /// The ABI name of the module, if it differs from the module name.
+  Identifier ModuleABIName;
+
 public:
   /// Produces the components of a given module's full name in reverse order.
   ///
@@ -343,6 +346,17 @@ class ModuleDecl : public DeclContext, public TypeDecl {
   void getDeclaredCrossImportBystanders(
       SmallVectorImpl<Identifier> &bystanderNames);
 
+  /// Retrieve the ABI name of the module, which is used for metadata and
+  /// mangling.
+  Identifier getABIName() const {
+    return ModuleABIName.empty() ? getName() : ModuleABIName;
+  }
+
+  /// Set the ABI name of the module;
+  void setABIName(Identifier name) {
+    ModuleABIName = name;
+  }
+
 private:
   /// A cache of this module's underlying module and required bystander if it's
   /// an underscored cross-import overlay.

include/swift/Frontend/FrontendOptions.h

@@ -48,9 +48,13 @@ class FrontendOptions {
   /// An Objective-C header to import and make implicitly visible.
   std::string ImplicitObjCHeaderPath;
 
-  /// The name of the module which the frontend is building.
+  /// The name of the module that the frontend is building.
   std::string ModuleName;
 
+  /// The ABI name of the module that the frontend is building, to be used in
+  /// mangling and metadata.
+  std::string ModuleABIName;
+
   /// The name of the library to link against when using this module.
   std::string ModuleLinkName;
 

include/swift/Option/Options.td

@@ -421,6 +421,9 @@ def module_link_name_EQ : Joined<["-"], "module-link-name=">,
 def autolink_force_load : Flag<["-"], "autolink-force-load">,
   Flags<[FrontendOption, ModuleInterfaceOption, HelpHidden]>,
   HelpText<"Force ld to link against this module even if no symbols are used">;
+def module_abi_name : Separate<["-"], "module-abi-name">,
+  Flags<[FrontendOption, ModuleInterfaceOption]>,
+  HelpText<"ABI name to use for the contents of this module">;
 
 def emit_module : Flag<["-"], "emit-module">,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild,

include/swift/Serialization/Validation.h

@@ -93,6 +93,7 @@ struct ValidationInfo {
 class ExtendedValidationInfo {
   SmallVector<StringRef, 4> ExtraClangImporterOpts;
   StringRef SDKPath;
+  StringRef ModuleABIName;
   struct {
     unsigned ArePrivateImportsEnabled : 1;
     unsigned IsSIB : 1;
@@ -145,6 +146,9 @@ class ExtendedValidationInfo {
   void setAllowModuleWithCompilerErrorsEnabled(bool val) {
     Bits.IsAllowModuleWithCompilerErrorsEnabled = val;
   }
+
+  StringRef getModuleABIName() const { return ModuleABIName; }
+  void setModuleABIName(StringRef name) { ModuleABIName = name; }
 };
 
 /// Returns info about the serialized AST in the given data.

lib/AST/ASTContext.cpp

@@ -164,6 +164,9 @@ struct ASTContext::Implementation {
   /// DenseMap.
   llvm::MapVector<Identifier, ModuleDecl *> LoadedModules;
 
+  /// The set of top-level modules we have loaded, indexed by ABI name.
+  llvm::MapVector<Identifier, ModuleDecl *> LoadedModulesByABIName;
+
   // FIXME: This is a StringMap rather than a StringSet because StringSet
   // doesn't allow passing in a pre-existing allocator.
   llvm::StringMap<Identifier::Aligner, llvm::BumpPtrAllocator&>

lib/AST/ASTMangler.cpp

@@ -2143,13 +2143,15 @@ void ASTMangler::appendModule(const ModuleDecl *module,
                               StringRef useModuleName) {
   assert(!module->getParent() && "cannot mangle nested modules!");
 
+  StringRef ModName =
+      DWARFMangling ? module->getName().str() : module->getABIName().str();
+
   // Try the special 'swift' substitution.
-  if (module->isStdlibModule()) {
+  if (ModName == STDLIB_NAME) {
     assert(useModuleName.empty());
     return appendOperator("s");
   }
 
-  StringRef ModName = module->getName().str();
   if (ModName == MANGLING_MODULE_OBJC) {
     assert(useModuleName.empty());
     return appendOperator("So");

lib/AST/Decl.cpp

@@ -638,6 +638,7 @@ StringRef Decl::getAlternateModuleName() const {
       }
     }
   }
+  
   for (auto *DC = getDeclContext(); DC; DC = DC->getParent()) {
     if (auto decl = DC->getAsDecl()) {
       if (decl == this)

lib/Driver/ToolChains.cpp

@@ -231,6 +231,7 @@ void ToolChain::addCommonFrontendArgs(const OutputInfo &OI,
   inputArgs.AddLastArg(arguments, options::OPT_import_underlying_module);
   inputArgs.AddLastArg(arguments, options::OPT_module_cache_path);
   inputArgs.AddLastArg(arguments, options::OPT_module_link_name);
+  inputArgs.AddLastArg(arguments, options::OPT_module_abi_name);
   inputArgs.AddLastArg(arguments, options::OPT_nostdimport);
   inputArgs.AddLastArg(arguments, options::OPT_parse_stdlib);
   inputArgs.AddLastArg(arguments, options::OPT_resource_dir);

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -217,6 +217,9 @@ bool ArgsToFrontendOptionsConverter::convert(
     return true;
   }
 
+  if (const Arg *A = Args.getLastArg(OPT_module_abi_name))
+    Opts.ModuleABIName = A->getValue();
+
   if (const Arg *A = Args.getLastArg(OPT_module_link_name))
     Opts.ModuleLinkName = A->getValue();
 

lib/Frontend/Frontend.cpp

@@ -925,7 +925,10 @@ ModuleDecl *CompilerInstance::getMainModule() const {
       MainModule->setPrivateImportsEnabled();
     if (Invocation.getFrontendOptions().EnableImplicitDynamic)
       MainModule->setImplicitDynamicEnabled();
-
+    if (!Invocation.getFrontendOptions().ModuleABIName.empty()) {
+      MainModule->setABIName(getASTContext().getIdentifier(
+          Invocation.getFrontendOptions().ModuleABIName));
+    }
     if (Invocation.getFrontendOptions().EnableLibraryEvolution)
       MainModule->setResilienceStrategy(ResilienceStrategy::Resilient);