1 files changed, 55 insertions, 181 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 9f9bf1e39c7..a87cf61ccfe 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4359,14 +4359,10 @@ TryToFixInvalidVariablyModifiedTypeSourceInfo(TypeSourceInfo *TInfo,
 /// function-scope declarations.
 void
 Sema::RegisterLocallyScopedExternCDecl(NamedDecl *ND, Scope *S) {
-  if (!getLangOpts().CPlusPlus &&
-      ND->getLexicalDeclContext()->getRedeclContext()->isTranslationUnit())
-    // Don't need to track declarations in the TU in C.
-    return;
-
+  assert(
+      !ND->getLexicalDeclContext()->getRedeclContext()->isTranslationUnit() &&
+      "Decl is not a locally-scoped decl!");
   // Note that we have a locally-scoped external with this name.
-  // FIXME: There can be multiple such declarations if they are functions marked
-  // __attribute__((overloadable)) declared in function scope in C.
   LocallyScopedExternCDecls[ND->getDeclName()] = ND;
 }
 
@@ -4685,32 +4681,6 @@ static bool isFunctionDefinitionDiscarded(Sema &S, FunctionDecl *FD) {
   return isC99Inline;
 }
 
-/// Determine whether a variable is extern "C" prior to attaching
-/// an initializer. We can't just call isExternC() here, because that
-/// will also compute and cache whether the declaration is externally
-/// visible, which might change when we attach the initializer.
-///
-/// This can only be used if the declaration is known to not be a
-/// redeclaration of an internal linkage declaration.
-///
-/// For instance:
-///
-///   auto x = []{};
-///
-/// Attaching the initializer here makes this declaration not externally
-/// visible, because its type has internal linkage.
-///
-/// FIXME: This is a hack.
-template<typename T>
-static bool isIncompleteDeclExternC(Sema &S, const T *D) {
-  if (S.getLangOpts().CPlusPlus) {
-    // In C++, the overloadable attribute negates the effects of extern "C".
-    if (!D->isInExternCContext() || D->template hasAttr<OverloadableAttr>())
-      return false;
-  }
-  return D->isExternC();
-}
-
 static bool shouldConsiderLinkage(const VarDecl *VD) {
   const DeclContext *DC = VD->getDeclContext()->getRedeclContext();
   if (DC->isFunctionOrMethod())
@@ -5100,10 +5070,16 @@ Sema::ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   ProcessPragmaWeak(S, NewVD);
   checkAttributesAfterMerging(*this, *NewVD);
 
-  // If this is the first declaration of an extern C variable, update
-  // the map of such variables.
-  if (!NewVD->getPreviousDecl() && !NewVD->isInvalidDecl() &&
-      isIncompleteDeclExternC(*this, NewVD))
+  // If this is the first declaration of an extern C variable that is not
+  // declared directly in the translation unit, update the map of such
+  // variables.
+  if (!CurContext->getRedeclContext()->isTranslationUnit() &&
+      !NewVD->getPreviousDecl() && !NewVD->isInvalidDecl() &&
+      // FIXME: We only check isExternC if we're in an extern C context,
+      // to avoid computing and caching an 'externally visible' flag which
+      // could change if the variable's type is not visible.
+      (!getLangOpts().CPlusPlus || NewVD->isInExternCContext()) &&
+      NewVD->isExternC())
     RegisterLocallyScopedExternCDecl(NewVD, S);
 
   return NewVD;
@@ -5204,120 +5180,30 @@ void Sema::CheckShadow(Scope *S, VarDecl *D) {
   CheckShadow(S, D, R);
 }
 
-/// Check for conflict between this global or extern "C" declaration and
-/// previous global or extern "C" declarations. This is only used in C++.
 template<typename T>
-static bool checkGlobalOrExternCConflict(
-    Sema &S, const T *ND, bool IsGlobal, LookupResult &Previous) {
-  assert(S.getLangOpts().CPlusPlus && "only C++ has extern \"C\"");
-  NamedDecl *Prev = S.findLocallyScopedExternCDecl(ND->getDeclName());
-
-  if (!Prev && IsGlobal && !isIncompleteDeclExternC(S, ND)) {
-    // The common case: this global doesn't conflict with any extern "C"
-    // declaration.
-    return false;
-  }
-
-  if (Prev) {
-    if (!IsGlobal || isIncompleteDeclExternC(S, ND)) {
-      // Both the old and new declarations have C language linkage. This is a
-      // redeclaration.
-      Previous.clear();
-      Previous.addDecl(Prev);
-      return true;
-    }
-
-    // This is a global, non-extern "C" declaration, and there is a previous
-    // non-global extern "C" declaration. Diagnose.
-  } else {
-    // The declaration is extern "C". Check for any declaration in the
-    // translation unit which might conflict.
-    if (IsGlobal) {
-      // We have already performed the lookup into the translation unit.
-      IsGlobal = false;
-      for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
-           I != E; ++I) {
-        if (isa<VarDecl>(*I) || isa<FunctionDecl>(*I)) {
-          Prev = *I;
-          break;
-        }
-      }
-    } else {
-      DeclContext::lookup_result R =
-          S.Context.getTranslationUnitDecl()->lookup(ND->getDeclName());
-      for (DeclContext::lookup_result::iterator I = R.begin(), E = R.end();
-           I != E; ++I) {
-        if (isa<VarDecl>(*I) || isa<FunctionDecl>(*I)) {
-          Prev = *I;
-          break;
-        }
-        // FIXME: If we have any other entity with this name in global scope,
-        // the declaration is ill-formed, but that is a defect: it breaks the
-        // 'stat' hack, for instance.
-      }
-    }
+static bool mayConflictWithNonVisibleExternC(const T *ND) {
+  const DeclContext *DC = ND->getDeclContext();
+  if (DC->getRedeclContext()->isTranslationUnit())
+    return true;
 
-    if (!Prev)
+  // We know that is the first decl we see, other than function local
+  // extern C ones. If this is C++ and the decl is not in a extern C context
+  // it cannot have C language linkage. Avoid calling isExternC in that case.
+  // We need to this because of code like
+  //
+  // namespace { struct bar {}; }
+  // auto foo = bar();
+  //
+  // This code runs before the init of foo is set, and therefore before
+  // the type of foo is known. Not knowing the type we cannot know its linkage
+  // unless it is in an extern C block.
+  if (!ND->isInExternCContext()) {
+    const ASTContext &Context = ND->getASTContext();
+    if (Context.getLangOpts().CPlusPlus)
       return false;
   }
 
-  // Use the first declaration's location to ensure we point at something which
-  // is lexically inside an extern "C" linkage-spec.
-  assert(Prev && "should have found a previous declaration to diagnose");
-  if (FunctionDecl *FD = dyn_cast<FunctionDecl>(Prev))
-    Prev = FD->getFirstDeclaration();
-  else
-    Prev = cast<VarDecl>(Prev)->getFirstDeclaration();
-
-  S.Diag(ND->getLocation(), diag::err_extern_c_global_conflict)
-    << IsGlobal << ND;
-  S.Diag(Prev->getLocation(), diag::note_extern_c_global_conflict)
-    << IsGlobal;
-  return false;
-}
-
-/// Apply special rules for handling extern "C" declarations. Returns \c true
-/// if we have found that this is a redeclaration of some prior entity.
-///
-/// Per C++ [dcl.link]p6:
-///   Two declarations [for a function or variable] with C language linkage
-///   with the same name that appear in different scopes refer to the same
-///   [entity]. An entity with C language linkage shall not be declared with
-///   the same name as an entity in global scope.
-template<typename T>
-static bool checkForConflictWithNonVisibleExternC(Sema &S, const T *ND,
-                                                  LookupResult &Previous) {
-  if (!S.getLangOpts().CPlusPlus) {
-    // In C, when declaring a global variable, look for a corresponding 'extern'
-    // variable declared in function scope.
-    //
-    // FIXME: The corresponding case in C++ does not work.  We should instead
-    // set the semantic DC for an extern local variable to be the innermost
-    // enclosing namespace, and ensure they are only found by redeclaration
-    // lookup.
-    if (ND->getDeclContext()->getRedeclContext()->isTranslationUnit()) {
-      if (NamedDecl *Prev = S.findLocallyScopedExternCDecl(ND->getDeclName())) {
-        Previous.clear();
-        Previous.addDecl(Prev);
-        return true;
-      }
-    }
-    return false;
-  }
-
-  // A declaration in the translation unit can conflict with an extern "C"
-  // declaration.
-  if (ND->getDeclContext()->getRedeclContext()->isTranslationUnit())
-    return checkGlobalOrExternCConflict(S, ND, /*IsGlobal*/true, Previous);
-
-  // An extern "C" declaration can conflict with a declaration in the
-  // translation unit or can be a redeclaration of an extern "C" declaration
-  // in another scope.
-  if (isIncompleteDeclExternC(S,ND))
-    return checkGlobalOrExternCConflict(S, ND, /*IsGlobal*/false, Previous);
-
-  // Neither global nor extern "C": nothing to do.
-  return false;
+  return ND->isExternC();
 }
 
 void Sema::CheckVariableDeclarationType(VarDecl *NewVD) {
@@ -5500,9 +5386,14 @@ bool Sema::CheckVariableDeclaration(VarDecl *NewVD,
   // The most important point here is that we're not allowed to
   // update our understanding of the type according to declarations
   // not in scope.
-  bool PreviousWasHidden =
-      Previous.empty() &&
-      checkForConflictWithNonVisibleExternC(*this, NewVD, Previous);
+  bool PreviousWasHidden = false;
+  if (Previous.empty() && mayConflictWithNonVisibleExternC(NewVD)) {
+    if (NamedDecl *ExternCPrev =
+            findLocallyScopedExternCDecl(NewVD->getDeclName())) {
+      Previous.addDecl(ExternCPrev);
+      PreviousWasHidden = true;
+    }
+  }
 
   // Filter out any non-conflicting previous declarations.
   filterNonConflictingPreviousDecls(Context, NewVD, Previous);
@@ -6734,10 +6625,12 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   // marking the function.
   AddCFAuditedAttribute(NewFD);
 
-  // If this is the first declaration of an extern C variable, update
-  // the map of such variables.
-  if (!NewFD->getPreviousDecl() && !NewFD->isInvalidDecl() &&
-      isIncompleteDeclExternC(*this, NewFD))
+  // If this is the first declaration of an extern C variable that is not
+  // declared directly in the translation unit, update the map of such
+  // variables.
+  if (!CurContext->getRedeclContext()->isTranslationUnit() &&
+      !NewFD->getPreviousDecl() && NewFD->isExternC() &&
+      !NewFD->isInvalidDecl())
     RegisterLocallyScopedExternCDecl(NewFD, S);
 
   // Set this FunctionDecl's range up to the right paren.
@@ -6841,6 +6734,15 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
   assert(!NewFD->getResultType()->isVariablyModifiedType() 
          && "Variably modified return types are not handled here");
 
+  // Check for a previous declaration of this name.
+  if (Previous.empty() && mayConflictWithNonVisibleExternC(NewFD)) {
+    // Since we did not find anything by this name, look for a non-visible
+    // extern "C" declaration with the same name.
+    if (NamedDecl *ExternCPrev =
+            findLocallyScopedExternCDecl(NewFD->getDeclName()))
+      Previous.addDecl(ExternCPrev);
+  }
+
   // Filter out any non-conflicting previous declarations.
   filterNonConflictingPreviousDecls(Context, NewFD, Previous);
 
@@ -6895,34 +6797,6 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
     }
   }
 
-  // Check for a previous extern "C" declaration with this name.
-  if (!Redeclaration &&
-      checkForConflictWithNonVisibleExternC(*this, NewFD, Previous)) {
-    filterNonConflictingPreviousDecls(Context, NewFD, Previous);
-    if (!Previous.empty()) {
-      // This is an extern "C" declaration with the same name as a previous
-      // declaration, and thus redeclares that entity...
-      Redeclaration = true;
-      OldDecl = Previous.getFoundDecl();
-
-      // ... except in the presence of __attribute__((overloadable)).
-      if (OldDecl->hasAttr<OverloadableAttr>()) {
-        if (!getLangOpts().CPlusPlus && !NewFD->hasAttr<OverloadableAttr>()) {
-          Diag(NewFD->getLocation(), diag::err_attribute_overloadable_missing)
-            << Redeclaration << NewFD;
-          Diag(Previous.getFoundDecl()->getLocation(),
-               diag::note_attribute_overloadable_prev_overload);
-          NewFD->addAttr(::new (Context) OverloadableAttr(SourceLocation(),
-                                                          Context));
-        }
-        if (IsOverload(NewFD, cast<FunctionDecl>(OldDecl), false)) {
-          Redeclaration = false;
-          OldDecl = 0;
-        }
-      }
-    }
-  }
-
   // C++11 [dcl.constexpr]p8:
   //   A constexpr specifier for a non-static member function that is not
   //   a constructor declares that member function to be const.