[modules] If we reach a definition of a class for which we already have a

non-visible definition, skip the new definition and make the old one visible
instead of trying to parse it again and failing horribly. C++'s ODR allows
us to assume that the two definitions are identical.

llvm-svn: 233250

3 files changed, 27 insertions, 10 deletions

diff --git a/clang/lib/Sema/SemaCXXScopeSpec.cpp b/clang/lib/Sema/SemaCXXScopeSpec.cpp
index 438ad61ee9b..9e146ed3a64 100644
--- a/clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ b/clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -218,6 +218,7 @@ bool Sema::RequireCompleteDeclContext(CXXScopeSpec &SS,
   // Fixed enum types are complete, but they aren't valid as scopes
   // until we see a definition, so awkwardly pull out this special
   // case.
+  // FIXME: The definition might not be visible; complain if it is not.
   const EnumType *enumType = dyn_cast_or_null<EnumType>(tagType);
   if (!enumType || enumType->getDecl()->isCompleteDefinition())
     return false;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 1234afb8fb7..ffd22390ee3 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16,6 +16,7 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
+#include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/CommentDiagnostic.h"
@@ -11233,13 +11234,16 @@ static FixItHint createFriendTagNNSFixIt(Sema &SemaRef, NamedDecl *ND, Scope *S,
   return FixItHint::CreateInsertion(NameLoc, Insertion);
 }
 
-/// ActOnTag - This is invoked when we see 'struct foo' or 'struct {'.  In the
+/// \brief This is invoked when we see 'struct foo' or 'struct {'.  In the
 /// former case, Name will be non-null.  In the later case, Name will be null.
 /// TagSpec indicates what kind of tag this is. TUK indicates whether this is a
 /// reference/declaration/definition of a tag.
 ///
-/// IsTypeSpecifier is true if this is a type-specifier (or
+/// \param IsTypeSpecifier \c true if this is a type-specifier (or
 /// trailing-type-specifier) other than one in an alias-declaration.
+///
+/// \param SkipBody If non-null, will be set to true if the caller should skip
+/// the definition of this tag, and treat it as if it were a declaration.
 Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation KWLoc, CXXScopeSpec &SS,
                      IdentifierInfo *Name, SourceLocation NameLoc,
@@ -11250,7 +11254,7 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation ScopedEnumKWLoc,
                      bool ScopedEnumUsesClassTag,
                      TypeResult UnderlyingType,
-                     bool IsTypeSpecifier) {
+                     bool IsTypeSpecifier, bool *SkipBody) {
   // If this is not a definition, it must have a name.
   IdentifierInfo *OrigName = Name;
   assert((Name != nullptr || TUK == TUK_Definition) &&
@@ -11676,7 +11680,7 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
 
           // Diagnose attempts to redefine a tag.
           if (TUK == TUK_Definition) {
-            if (TagDecl *Def = PrevTagDecl->getDefinition()) {
+            if (NamedDecl *Def = PrevTagDecl->getDefinition()) {
               // If we're defining a specialization and the previous definition
               // is from an implicit instantiation, don't emit an error
               // here; we'll catch this in the general case below.
@@ -11692,7 +11696,19 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                     TSK_ExplicitSpecialization;
               }
 
-              if (!IsExplicitSpecializationAfterInstantiation) {
+              if (SkipBody && getLangOpts().CPlusPlus &&
+                  !hasVisibleDefinition(Def, &Def)) {
+                // There is a definition of this tag, but it is not visible. We
+                // explicitly make use of C++'s one definition rule here, and
+                // assume that this definition is identical to the hidden one
+                // we already have. Make the existing definition visible and
+                // use it in place of this one.
+                *SkipBody = true;
+                if (auto *Listener = getASTMutationListener())
+                  Listener->RedefinedHiddenDefinition(Def, KWLoc);
+                Def->setHidden(false);
+                return Def;
+              } else if (!IsExplicitSpecializationAfterInstantiation) {
                 // A redeclaration in function prototype scope in C isn't
                 // visible elsewhere, so merely issue a warning.
                 if (!getLangOpts().CPlusPlus && S->containedInPrototypeScope())
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 669cb9a9772..485b70a4f9b 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -5126,9 +5126,9 @@ bool Sema::RequireCompleteType(SourceLocation Loc, QualType T,
 /// \param D The definition of the entity.
 /// \param Suggested Filled in with the declaration that should be made visible
 ///        in order to provide a definition of this entity.
-static bool hasVisibleDefinition(Sema &S, NamedDecl *D, NamedDecl **Suggested) {
+bool Sema::hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested) {
   // Easy case: if we don't have modules, all declarations are visible.
-  if (!S.getLangOpts().Modules)
+  if (!getLangOpts().Modules)
     return true;
 
   // If this definition was instantiated from a template, map back to the
@@ -5144,7 +5144,7 @@ static bool hasVisibleDefinition(Sema &S, NamedDecl *D, NamedDecl **Suggested) {
       // If the enum has a fixed underlying type, any declaration of it will do.
       *Suggested = nullptr;
       for (auto *Redecl : ED->redecls()) {
-        if (LookupResult::isVisible(S, Redecl))
+        if (LookupResult::isVisible(*this, Redecl))
           return true;
         if (Redecl->isThisDeclarationADefinition() ||
             (Redecl->isCanonicalDecl() && !*Suggested))
@@ -5159,7 +5159,7 @@ static bool hasVisibleDefinition(Sema &S, NamedDecl *D, NamedDecl **Suggested) {
   // FIXME: If we merged any other decl into D, and that declaration is visible,
   // then we should consider a definition to be visible.
   *Suggested = D;
-  return LookupResult::isVisible(S, D);
+  return LookupResult::isVisible(*this, D);
 }
 
 /// Locks in the inheritance model for the given class and all of its bases.
@@ -5210,7 +5210,7 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
     // If we know about the definition but it is not visible, complain.
     NamedDecl *SuggestedDef = nullptr;
     if (!Diagnoser.Suppressed && Def &&
-        !hasVisibleDefinition(*this, Def, &SuggestedDef)) {
+        !hasVisibleDefinition(Def, &SuggestedDef)) {
       // Suppress this error outside of a SFINAE context if we've already
       // emitted the error once for this type. There's no usefulness in
       // repeating the diagnostic.