Sema: Keep public module name in ModuleDecl

Author: xymus

include/swift/AST/Module.h

@@ -243,6 +243,8 @@ class ModuleDecl
   /// Module name to use when referenced in clients module interfaces.
   mutable Identifier ExportAsName;
 
+  mutable Identifier PublicModuleName;
+
 public:
   /// Produces the components of a given module's full name in reverse order.
   ///
@@ -504,6 +506,21 @@ class ModuleDecl
     ExportAsName = name;
   }
 
+  /// Public facing name for this module in diagnostics and documentation.
+  ///
+  /// This always returns a valid name as it defaults to the module name if
+  /// no public module name is set.
+  ///
+  /// If `mustBeVisible`, return the normal module name when the module
+  /// corresponding to the public module name isn't imported. Users working
+  /// in between both modules will then see the normal module name,
+  /// this may be more useful for diagnostics at that level.
+  Identifier getPublicModuleName(bool mustBeVisible) const;
+
+  void setPublicModuleName(Identifier name) {
+    PublicModuleName = name;
+  }
+
   /// Retrieve the actual module name of an alias used for this module (if any).
   ///
   /// For example, if '-module-alias Foo=Bar' is passed in when building the main module,

lib/AST/Module.cpp

@@ -1922,6 +1922,19 @@ ImportedModule::removeDuplicates(SmallVectorImpl<ImportedModule> &imports) {
   imports.erase(last, imports.end());
 }
 
+Identifier ModuleDecl::getPublicModuleName(bool mustBeVisible) const {
+  if (!PublicModuleName.empty()) {
+    if (!mustBeVisible)
+      return PublicModuleName;
+
+    bool publicModuleIsImported =
+      getASTContext().getModuleByIdentifier(PublicModuleName);
+    if (publicModuleIsImported)
+      return PublicModuleName;
+  }
+  return getName();
+}
+
 Identifier ModuleDecl::getRealName() const {
   // This will return the real name for an alias (if used) or getName()
   return getASTContext().getRealModuleName(getName());

lib/Frontend/Frontend.cpp

@@ -1463,6 +1463,10 @@ ModuleDecl *CompilerInstance::getMainModule() const {
       MainModule->setExportAsName(getASTContext().getIdentifier(
           Invocation.getFrontendOptions().ExportAsName));
     }
+    if (!Invocation.getFrontendOptions().PublicModuleName.empty()) {
+      MainModule->setPublicModuleName(getASTContext().getIdentifier(
+          Invocation.getFrontendOptions().PublicModuleName));
+    }
     if (Invocation.getFrontendOptions().EnableLibraryEvolution)
       MainModule->setResilienceStrategy(ResilienceStrategy::Resilient);
     if (Invocation.getLangOptions().isSwiftVersionAtLeast(6))

lib/Serialization/Serialization.cpp

@@ -1126,6 +1126,13 @@ void Serializer::writeHeader() {
         ExportAs.emit(ScratchRecord, M->getExportAsName().str());
       }
 
+      Identifier publicModuleName =
+        M->getPublicModuleName(/*mustBeVisible=*/false);
+      if (publicModuleName != M->getName()) {
+        options_block::PublicModuleNameLayout PublicModuleName(Out);
+        PublicModuleName.emit(ScratchRecord, publicModuleName.str());
+      }
+
       if (M->isConcurrencyChecked()) {
         options_block::IsConcurrencyCheckedLayout IsConcurrencyChecked(Out);
         IsConcurrencyChecked.emit(ScratchRecord);

lib/Serialization/SerializedModuleLoader.cpp

@@ -953,6 +953,8 @@ LoadedFile *SerializedModuleLoaderBase::loadAST(
       M.setSerializePackageEnabled();
     if (!loadedModuleFile->getModuleABIName().empty())
       M.setABIName(Ctx.getIdentifier(loadedModuleFile->getModuleABIName()));
+    if (!loadedModuleFile->getPublicModuleName().empty())
+      M.setPublicModuleName(Ctx.getIdentifier(loadedModuleFile->getPublicModuleName()));
     if (loadedModuleFile->isConcurrencyChecked())
       M.setIsConcurrencyChecked();
     if (loadedModuleFile->hasCxxInteroperability()) {