[NFC] [C++20] [Modules] Refactor Sema::isModuleUnitOfCurrentTU into

Decl::isInAnotherModuleUnit

Refactor `Sema::isModuleUnitOfCurrentTU` to `Decl::isInAnotherModuleUnit`
to make code simpler a little bit. Note that although this patch
introduces a FIXME, this is an existing issue and this patch just tries
to describe it explicitly.

clang/include/clang/AST/ASTContext.h

@@ -448,7 +448,7 @@ class ASTContext : public RefCountedBase<ASTContext> {
   llvm::DenseMap<Module*, PerModuleInitializers*> ModuleInitializers;
 
   /// This is the top-level (C++20) Named module we are building.
-   Module *CurrentCXXNamedModule = nullptr;
+  Module *CurrentCXXNamedModule = nullptr;
 
   static constexpr unsigned ConstantArrayTypesLog2InitSize = 8;
   static constexpr unsigned GeneralTypesLog2InitSize = 9;

clang/include/clang/AST/DeclBase.h

@@ -644,6 +644,9 @@ class alignas(8) Decl {
     return getModuleOwnershipKind() > ModuleOwnershipKind::VisibleWhenImported;
   }
 
+  /// Whether this declaration comes from another module unit.
+  bool isInAnotherModuleUnit() const;
+
   /// FIXME: Implement discarding declarations actually in global module
   /// fragment. See [module.global.frag]p3,4 for details.
   bool isDiscardedInGlobalModuleFragment() const { return false; }

clang/include/clang/Sema/Sema.h

@@ -2364,9 +2364,6 @@ class Sema final {
     return Entity->getOwningModule();
   }
 
-  // Determine whether the module M belongs to the  current TU.
-  bool isModuleUnitOfCurrentTU(const Module *M) const;
-
   /// Make a merged definition of an existing hidden definition \p ND
   /// visible at the specified location.
   void makeMergedDefinitionVisible(NamedDecl *ND);

clang/lib/AST/ASTContext.cpp

@@ -1155,7 +1155,7 @@ ArrayRef<Decl *> ASTContext::getModuleInitializers(Module *M) {
 void ASTContext::setCurrentNamedModule(Module *M) {
   assert(M->isModulePurview());
   assert(!CurrentCXXNamedModule &&
-        "We should set named module for ASTContext for only once");
+         "We should set named module for ASTContext for only once");
   CurrentCXXNamedModule = M;
 }
 
@@ -11935,9 +11935,7 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
     return false;
 
   // Variables in other module units shouldn't be forced to be emitted.
-  auto *VM = VD->getOwningModule();
-  if (VM && VM->getTopLevelModule()->isModulePurview() &&
-      VM->getTopLevelModule() != getCurrentNamedModule())
+  if (VD->isInAnotherModuleUnit())
     return false;
 
   // Variables that can be needed in other TUs are required.

clang/lib/AST/DeclBase.cpp

@@ -30,6 +30,7 @@
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
+#include "clang/Basic/Module.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Basic/PartialDiagnostic.h"
 #include "clang/Basic/SourceLocation.h"
@@ -1022,6 +1023,28 @@ bool Decl::isInExportDeclContext() const {
   return DC && isa<ExportDecl>(DC);
 }
 
+bool Decl::isInAnotherModuleUnit() const {
+  auto *M = getOwningModule();
+
+  if (!M)
+    return false;
+
+  M = M->getTopLevelModule();
+  // FIXME: It is problematic if the header module lives in another module
+  // unit. Consider to fix this by techniques like
+  // ExternalASTSource::hasExternalDefinitions.
+  if (M->isHeaderLikeModule())
+    return false;
+
+  // A global module without parent implies that we're parsing the global
+  // module. So it can't be in another module unit.
+  if (M->isGlobalModule())
+    return false;
+
+  assert(M->isModulePurview() && "New module kind?");
+  return M != getASTContext().getCurrentNamedModule();
+}
+
 static Decl::Kind getKind(const Decl *D) { return D->getKind(); }
 static Decl::Kind getKind(const DeclContext *DC) { return DC->getDeclKind(); }
 

clang/lib/Sema/SemaLookup.cpp

@@ -1905,14 +1905,11 @@ bool LookupResult::isReachableSlow(Sema &SemaRef, NamedDecl *D) {
   Module *DeclModule = SemaRef.getOwningModule(D);
   assert(DeclModule && "hidden decl has no owning module");
 
-  // Entities in module map modules are reachable only if they're visible.
-  if (DeclModule->isModuleMapModule())
+  // Entities in header like modules are reachable only if they're visible.
+  if (DeclModule->isHeaderLikeModule())
     return false;
 
-  // If D comes from a module and SemaRef doesn't own a module, it implies D
-  // comes from another TU. In case SemaRef owns a module, we could judge if D
-  // comes from another TU by comparing the module unit.
-  if (SemaRef.isModuleUnitOfCurrentTU(DeclModule))
+  if (!D->isInAnotherModuleUnit())
     return true;
 
   // [module.reach]/p3:
@@ -3893,7 +3890,7 @@ void Sema::ArgumentDependentLookup(DeclarationName Name, SourceLocation Loc,
                    "bad export context");
             // .. are attached to a named module M, do not appear in the
             // translation unit containing the point of the lookup..
-            if (!isModuleUnitOfCurrentTU(FM) &&
+            if (D->isInAnotherModuleUnit() &&
                 llvm::any_of(AssociatedClasses, [&](auto *E) {
                   // ... and have the same innermost enclosing non-inline
                   // namespace scope as a declaration of an associated entity

clang/lib/Sema/SemaModule.cpp

@@ -1024,16 +1024,3 @@ void Sema::PopImplicitGlobalModuleFragment() {
          "left the wrong module scope, which is not global module fragment");
   ModuleScopes.pop_back();
 }
-
-bool Sema::isModuleUnitOfCurrentTU(const Module *M) const {
-  assert(M);
-
-  Module *CurrentModuleUnit = getCurrentModule();
-
-  // If we are not in a module currently, M must not be the module unit of
-  // current TU.
-  if (!CurrentModuleUnit)
-    return false;
-
-  return M->isSubModuleOf(CurrentModuleUnit->getTopLevelModule());
-}

clang/lib/Sema/SemaOverload.cpp

@@ -6543,23 +6543,20 @@ void Sema::AddOverloadCandidate(
   }
 
   // Functions with internal linkage are only viable in the same module unit.
-  if (auto *MF = Function->getOwningModule()) {
-    if (getLangOpts().CPlusPlusModules && !MF->isModuleMapModule() &&
-        !isModuleUnitOfCurrentTU(MF)) {
-      /// FIXME: Currently, the semantics of linkage in clang is slightly
-      /// different from the semantics in C++ spec. In C++ spec, only names
-      /// have linkage. So that all entities of the same should share one
-      /// linkage. But in clang, different entities of the same could have
-      /// different linkage.
-      NamedDecl *ND = Function;
-      if (auto *SpecInfo = Function->getTemplateSpecializationInfo())
-        ND = SpecInfo->getTemplate();
-
-      if (ND->getFormalLinkage() == Linkage::InternalLinkage) {
-        Candidate.Viable = false;
-        Candidate.FailureKind = ovl_fail_module_mismatched;
-        return;
-      }
+  if (getLangOpts().CPlusPlusModules && Function->isInAnotherModuleUnit()) {
+    /// FIXME: Currently, the semantics of linkage in clang is slightly
+    /// different from the semantics in C++ spec. In C++ spec, only names
+    /// have linkage. So that all entities of the same should share one
+    /// linkage. But in clang, different entities of the same could have
+    /// different linkage.
+    NamedDecl *ND = Function;
+    if (auto *SpecInfo = Function->getTemplateSpecializationInfo())
+      ND = SpecInfo->getTemplate();
+
+    if (ND->getFormalLinkage() == Linkage::InternalLinkage) {
+      Candidate.Viable = false;
+      Candidate.FailureKind = ovl_fail_module_mismatched;
+      return;
     }
   }
 

clang/lib/Sema/SemaTemplate.cpp

@@ -2851,8 +2851,7 @@ bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
         NewDefaultLoc = NewTypeParm->getDefaultArgumentLoc();
         SawDefaultArgument = true;
 
-        if (!OldTypeParm->getOwningModule() ||
-            isModuleUnitOfCurrentTU(OldTypeParm->getOwningModule()))
+        if (!OldTypeParm->getOwningModule())
           RedundantDefaultArg = true;
         else if (!getASTContext().isSameDefaultTemplateArgument(OldTypeParm,
                                                                 NewTypeParm)) {
@@ -2904,8 +2903,7 @@ bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
         OldDefaultLoc = OldNonTypeParm->getDefaultArgumentLoc();
         NewDefaultLoc = NewNonTypeParm->getDefaultArgumentLoc();
         SawDefaultArgument = true;
-        if (!OldNonTypeParm->getOwningModule() ||
-            isModuleUnitOfCurrentTU(OldNonTypeParm->getOwningModule()))
+        if (!OldNonTypeParm->getOwningModule())
           RedundantDefaultArg = true;
         else if (!getASTContext().isSameDefaultTemplateArgument(
                      OldNonTypeParm, NewNonTypeParm)) {
@@ -2956,8 +2954,7 @@ bool Sema::CheckTemplateParameterList(TemplateParameterList *NewParams,
         OldDefaultLoc = OldTemplateParm->getDefaultArgument().getLocation();
         NewDefaultLoc = NewTemplateParm->getDefaultArgument().getLocation();
         SawDefaultArgument = true;
-        if (!OldTemplateParm->getOwningModule() ||
-            isModuleUnitOfCurrentTU(OldTemplateParm->getOwningModule()))
+        if (!OldTemplateParm->getOwningModule())
           RedundantDefaultArg = true;
         else if (!getASTContext().isSameDefaultTemplateArgument(
                      OldTemplateParm, NewTemplateParm)) {

clang/test/Modules/redundant-template-default-arg4.cpp

@@ -0,0 +1,40 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -x c++ -std=c++20 -fmodules -fmodule-name=foo %t/foo.map -emit-module -o %t/foo.pcm
+// RUN: %clang_cc1 -x c++ -std=c++20 -fmodules -fmodules-cache-path=%t \
+// RUN:     -fmodule-file=%t/foo.pcm %t/use.cpp -verify -fsyntax-only
+
+//--- foo.map
+module "foo" {
+  export * 
+  header "foo.h"
+}
+
+//--- foo.h
+template<class T1, int V = 0>
+class A;
+
+template <typename T>
+class templ_params {};
+
+template<class T1, template <typename> typename T2 = templ_params>
+class B;
+
+template<class T1, class T2 = int>
+class C;
+
+//--- use.cpp
+#include "foo.h"
+template<class T1, int V = 1> // expected-error {{template parameter default argument is inconsistent with previous definition}}
+class A;   // expected-note@foo.h:1 {{previous default template argument defined in module foo}}
+
+template <typename T>
+class templ_params2 {};
+
+template<class T1, template <typename> typename T2 = templ_params2> // expected-error {{template parameter default argument is inconsistent with previous definition}}
+class B; // expected-note@foo.h:7 {{previous default template argument defined in module foo}}
+
+template<class T1, class T2 = double> // expected-error {{template parameter default argument is inconsistent with previous definition}}
+class C; // expected-note@foo.h:10 {{previous default template argument defined in module foo}}

clang/test/Modules/redundant-template-default-arg5.cpp

@@ -0,0 +1,30 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -fmodules -fmodule-name=mod -xc++ -emit-module %t/mod.cppmap -o %t/mod.pcm
+// RUN: %clang_cc1 -std=c++20 -fmodules -fmodule-file=%t/mod.pcm -fsyntax-only %t/use.cc -verify
+
+//--- mod.cppmap
+module "mod" {
+  export *
+  header "mod.h"
+}
+
+//--- mod.h
+#ifndef MOD
+#define MOD
+#include "templ.h"
+#endif
+
+//--- templ.h
+#ifndef TEMPL
+#define TEMPL
+template <typename t1 = void>
+inline constexpr bool inl = false;
+#endif
+
+//--- use.cc
+// expected-no-diagnostics
+#include "templ.h"
+#include "mod.h"