From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 3 Jan 2018 23:03:54 +0000 (+0000)
Subject: PR33503: When a qualified name in a redeclaration names a prior declaration in
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3536cf01514107b288e5230eeafeefc0dc89ff76;p=clang

PR33503: When a qualified name in a redeclaration names a prior declaration in
an inline namespace, update its semantic DeclContext to match.

We would previously get the semantic DeclContext wrong (pointing to the named
scope rather than the inline namespace within it), resulting in wrong lookup
results and linkage-related problems if the inline namespace was an anonymous
namespace.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321770 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 743f4bb5e8..73952ad38a 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2929,6 +2929,48 @@ static bool hasIdenticalPassObjectSizeAttrs(const FunctionDecl *A,
   return std::equal(A->param_begin(), A->param_end(), B->param_begin(), AttrEq);
 }
 
+/// If necessary, adjust the semantic declaration context for a qualified
+/// declaration to name the correct inline namespace within the qualifier.
+static void adjustDeclContextForDeclaratorDecl(DeclaratorDecl *NewD,
+                                               DeclaratorDecl *OldD) {
+  // The only case where we need to update the DeclContext is when
+  // redeclaration lookup for a qualified name finds a declaration
+  // in an inline namespace within the context named by the qualifier:
+  //
+  //   inline namespace N { int f(); }
+  //   int ::f(); // Sema DC needs adjusting from :: to N::.
+  //
+  // For unqualified declarations, the semantic context *can* change
+  // along the redeclaration chain (for local extern declarations,
+  // extern "C" declarations, and friend declarations in particular).
+  if (!NewD->getQualifier())
+    return;
+
+  // NewD is probably already in the right context.
+  auto *NamedDC = NewD->getDeclContext()->getRedeclContext();
+  auto *SemaDC = OldD->getDeclContext()->getRedeclContext();
+  if (NamedDC->Equals(SemaDC))
+    return;
+
+  assert((NamedDC->InEnclosingNamespaceSetOf(SemaDC) ||
+          NewD->isInvalidDecl() || OldD->isInvalidDecl()) &&
+         "unexpected context for redeclaration");
+
+  auto *LexDC = NewD->getLexicalDeclContext();
+  auto FixSemaDC = [=](NamedDecl *D) {
+    if (!D)
+      return;
+    D->setDeclContext(SemaDC);
+    D->setLexicalDeclContext(LexDC);
+  };
+
+  FixSemaDC(NewD);
+  if (auto *FD = dyn_cast<FunctionDecl>(NewD))
+    FixSemaDC(FD->getDescribedFunctionTemplate());
+  else if (auto *VD = dyn_cast<VarDecl>(NewD))
+    FixSemaDC(VD->getDescribedVarTemplate());
+}
+
 /// MergeFunctionDecl - We just parsed a function 'New' from
 /// declarator D which has the same name and scope as a previous
 /// declaration 'Old'.  Figure out how to resolve this situation,
@@ -3953,6 +3995,7 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
   New->setPreviousDecl(Old);
   if (NewTemplate)
     NewTemplate->setPreviousDecl(OldTemplate);
+  adjustDeclContextForDeclaratorDecl(New, Old);
 
   // Inherit access appropriately.
   New->setAccess(Old->getAccess());
@@ -9252,12 +9295,13 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
 
     if (FunctionTemplateDecl *OldTemplateDecl
                                   = dyn_cast<FunctionTemplateDecl>(OldDecl)) {
-      NewFD->setPreviousDeclaration(OldTemplateDecl->getTemplatedDecl());
+      auto *OldFD = OldTemplateDecl->getTemplatedDecl();
+      NewFD->setPreviousDeclaration(OldFD);
+      adjustDeclContextForDeclaratorDecl(NewFD, OldFD);
       FunctionTemplateDecl *NewTemplateDecl
         = NewFD->getDescribedFunctionTemplate();
       assert(NewTemplateDecl && "Template/non-template mismatch");
-      if (CXXMethodDecl *Method
-            = dyn_cast<CXXMethodDecl>(NewTemplateDecl->getTemplatedDecl())) {
+      if (auto *Method = dyn_cast<CXXMethodDecl>(NewFD)) {
         Method->setAccess(OldTemplateDecl->getAccess());
         NewTemplateDecl->setAccess(OldTemplateDecl->getAccess());
       }
@@ -9270,22 +9314,22 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
         assert(OldTemplateDecl->isMemberSpecialization());
         // Explicit specializations of a member template do not inherit deleted
         // status from the parent member template that they are specializing.
-        if (OldTemplateDecl->getTemplatedDecl()->isDeleted()) {
-          FunctionDecl *const OldTemplatedDecl =
-              OldTemplateDecl->getTemplatedDecl();
+        if (OldFD->isDeleted()) {
           // FIXME: This assert will not hold in the presence of modules.
-          assert(OldTemplatedDecl->getCanonicalDecl() == OldTemplatedDecl);
+          assert(OldFD->getCanonicalDecl() == OldFD);
           // FIXME: We need an update record for this AST mutation.
-          OldTemplatedDecl->setDeletedAsWritten(false);
+          OldFD->setDeletedAsWritten(false);
         }
       }
 
     } else {
       if (shouldLinkDependentDeclWithPrevious(NewFD, OldDecl)) {
+        auto *OldFD = cast<FunctionDecl>(OldDecl);
         // This needs to happen first so that 'inline' propagates.
-        NewFD->setPreviousDeclaration(cast<FunctionDecl>(OldDecl));
+        NewFD->setPreviousDeclaration(OldFD);
+        adjustDeclContextForDeclaratorDecl(NewFD, OldFD);
         if (isa<CXXMethodDecl>(NewFD))
-          NewFD->setAccess(OldDecl->getAccess());
+          NewFD->setAccess(OldFD->getAccess());
       }
     }
   } else if (!getLangOpts().CPlusPlus && MayNeedOverloadableChecks &&
diff --git a/test/CXX/dcl.decl/dcl.meaning/p1-0x.cpp b/test/CXX/dcl.decl/dcl.meaning/p1-0x.cpp
index 1d04d7d2a7..fbe9c0895a 100644
--- a/test/CXX/dcl.decl/dcl.meaning/p1-0x.cpp
+++ b/test/CXX/dcl.decl/dcl.meaning/p1-0x.cpp
@@ -101,4 +101,25 @@ namespace inline_namespaces {
   template<> struct N::V<int> {};
   template struct N::V<int*>;
   template struct N::V<char>; // expected-error {{undefined}}
+
+  struct Q {};
+
+  // Perversely, inline anonymous namespaces can cause an ostensibly
+  // external-linkage declaration to acquire internal linkage when
+  // redeclared with a qualified name.
+  inline namespace {
+    struct Q {} q;
+    int f_in_inline();
+    extern int v_in_inline;
+    typedef int t_in_inline;
+  }
+  // FIXME: These "extra qualification" warnings are bogus: the qualification
+  // changes the meaning of the program.
+  int inline_namespaces::f_in_inline() { // expected-warning {{extra qualification}}
+    // Finds <anon>::Q, not inline_namespaces::Q
+    Q x = q;
+    return 0;
+  }
+  int inline_namespaces::v_in_inline = // expected-warning {{extra qualification}}
+    (Q(q), 0);
 }