[C++20][Modules][2/8] Add enumerations for partition modules and stream them.

This is an initial enabling patch for module partition support.
We add enumerations for partition interfaces/implementations.

This means that the module kind enumeration now occupies three
bits, so the AST streamer is adjusted for this.  Adding one bit there
seems preferable to trying to overload the meanings of existing
kinds (and we will also want to add a C++20 header unit case later).

Differential Revision: https://reviews.llvm.org/D114714

clang/include/clang/Basic/Module.h

@@ -106,9 +106,15 @@ public:
     /// of header files.
     ModuleMapModule,
 
-    /// This is a C++ Modules TS module interface unit.
+    /// This is a C++20 module interface unit.
     ModuleInterfaceUnit,
 
+    /// This is a C++ 20 module partition interface.
+    ModulePartitionInterface,
+
+    /// This is a C++ 20 module partition implementation.
+    ModulePartitionImplementation,
+
     /// This is a fragment of the global module within some C++ module.
     GlobalModuleFragment,
 
@@ -150,7 +156,9 @@ public:
 
   /// Does this Module scope describe part of the purview of a named C++ module?
   bool isModulePurview() const {
-    return Kind == ModuleInterfaceUnit || Kind == PrivateModuleFragment;
+    return Kind == ModuleInterfaceUnit || Kind == ModulePartitionInterface ||
+           Kind == ModulePartitionImplementation ||
+           Kind == PrivateModuleFragment;
   }
 
   /// Does this Module scope describe a fragment of the global module within
@@ -506,6 +514,9 @@ public:
     Parent->SubModules.push_back(this);
   }
 
+  /// Is this a module partition.
+  bool isModulePartition() const { return Name.find(':') != std::string::npos; }
+
   /// Retrieve the full name of this module, including the path from
   /// its top-level module.
   /// \param AllowStringLiterals If \c true, components that might not be

clang/lib/AST/Decl.cpp

@@ -1550,6 +1550,8 @@ Module *Decl::getOwningModuleForLinkage(bool IgnoreLinkage) const {
     return nullptr;
 
   case Module::ModuleInterfaceUnit:
+  case Module::ModulePartitionInterface:
+  case Module::ModulePartitionImplementation:
     return M;
 
   case Module::GlobalModuleFragment: {

clang/lib/Sema/SemaModule.cpp

@@ -261,6 +261,8 @@ Sema::ActOnPrivateModuleFragmentDecl(SourceLocation ModuleLoc,
                                : ModuleScopes.back().Module->Kind) {
   case Module::ModuleMapModule:
   case Module::GlobalModuleFragment:
+  case Module::ModulePartitionImplementation:
+  case Module::ModulePartitionInterface:
     Diag(PrivateLoc, diag::err_private_module_fragment_not_module);
     return nullptr;
 

clang/lib/Serialization/ASTWriter.cpp

@@ -2674,7 +2674,7 @@ void ASTWriter::WriteSubmodules(Module *WritingModule) {
   Abbrev->Add(BitCodeAbbrevOp(SUBMODULE_DEFINITION));
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // ID
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Parent
-  Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 2)); // Kind
+  Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3)); // Kind
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsFramework
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsExplicit
   Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // IsSystem