Add missing diagnostic for explicit instantiation declarations naming

internal linkage entities.

Such constructs are ill-formed by [temp.explicit]p13. We make a special
exception to permit an invalid construct used by libc++ in some build
modes: its <valarray> header declares some functions with the
internal_linkage attribute and then (meaninglessly) provides explicit
instantiation declarations for them. Luckily, Clang happens to
effectively ignore the explicit instantiation declaration when
generating code in this case, and this change codifies that behavior.

This reinstates part of r359048, reverted in r359076. (The libc++ issue
triggering the rollback has been addressed.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359259 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 238c9eec70c8e717b99c046d4d2c5dcc46c1e5df..059183dbaf1e8dc0893c1544b32735623223d3ed 100644 (file)
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4384,6 +4384,8 @@ def err_explicit_instantiation_of_typedef : Error<
   "explicit instantiation of typedef %0">;
 def err_explicit_instantiation_storage_class : Error<
   "explicit instantiation cannot have a storage class">;
+def err_explicit_instantiation_internal_linkage : Error<
+  "explicit instantiation declaration of %0 with internal linkage">;
 def err_explicit_instantiation_not_known : Error<
   "explicit instantiation of %0 does not refer to a function template, "
   "variable template, member function, member class, or static data member">;

diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 101037083842785bac2d5b57ad7d860247e13ac1..973911eb840c5bd007e5b4e789e17504f9adcc9a 100644 (file)
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -8619,6 +8619,29 @@ static bool CheckExplicitInstantiationScope(Sema &S, NamedDecl *D,
   return false;
 }
 
+/// Common checks for whether an explicit instantiation of \p D is valid.
+static bool CheckExplicitInstantiation(Sema &S, NamedDecl *D,
+                                       SourceLocation InstLoc,
+                                       bool WasQualifiedName,
+                                       TemplateSpecializationKind TSK) {
+  // C++ [temp.explicit]p13:
+  //   An explicit instantiation declaration shall not name a specialization of
+  //   a template with internal linkage.
+  if (TSK == TSK_ExplicitInstantiationDeclaration &&
+      D->getFormalLinkage() == InternalLinkage) {
+    S.Diag(InstLoc, diag::err_explicit_instantiation_internal_linkage) << D;
+    return true;
+  }
+
+  // C++11 [temp.explicit]p3: [DR 275]
+  //   An explicit instantiation shall appear in an enclosing namespace of its
+  //   template.
+  if (CheckExplicitInstantiationScope(S, D, InstLoc, WasQualifiedName))
+    return true;
+
+  return false;
+}
+
 /// Determine whether the given scope specifier has a template-id in it.
 static bool ScopeSpecifierHasTemplateId(const CXXScopeSpec &SS) {
   if (!SS.isSet())
@@ -8770,13 +8793,8 @@ DeclResult Sema::ActOnExplicitInstantiation(
   TemplateSpecializationKind PrevDecl_TSK
     = PrevDecl ? PrevDecl->getTemplateSpecializationKind() : TSK_Undeclared;
 
-  // C++0x [temp.explicit]p2:
-  //   [...] An explicit instantiation shall appear in an enclosing
-  //   namespace of its template. [...]
-  //
-  // This is C++ DR 275.
-  if (CheckExplicitInstantiationScope(*this, ClassTemplate, TemplateNameLoc,
-                                      SS.isSet()))
+  if (CheckExplicitInstantiation(*this, ClassTemplate, TemplateNameLoc,
+                                 SS.isSet(), TSK))
     return true;
 
   ClassTemplateSpecializationDecl *Specialization = nullptr;
@@ -8999,12 +9017,7 @@ Sema::ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
     = ExternLoc.isInvalid()? TSK_ExplicitInstantiationDefinition
                            : TSK_ExplicitInstantiationDeclaration;
 
-  // C++0x [temp.explicit]p2:
-  //   [...] An explicit instantiation shall appear in an enclosing
-  //   namespace of its template. [...]
-  //
-  // This is C++ DR 275.
-  CheckExplicitInstantiationScope(*this, Record, NameLoc, true);
+  CheckExplicitInstantiation(*this, Record, NameLoc, true, TSK);
 
   // Verify that it is okay to explicitly instantiate here.
   CXXRecordDecl *PrevDecl
@@ -9235,8 +9248,7 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
            diag::ext_explicit_instantiation_without_qualified_id)
         << Prev << D.getCXXScopeSpec().getRange();
 
-    // Check the scope of this explicit instantiation.
-    CheckExplicitInstantiationScope(*this, Prev, D.getIdentifierLoc(), true);
+    CheckExplicitInstantiation(*this, Prev, D.getIdentifierLoc(), true, TSK);
 
     // Verify that it is okay to explicitly instantiate here.
     TemplateSpecializationKind PrevTSK = Prev->getTemplateSpecializationKind();
@@ -9411,6 +9423,20 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
       return (Decl*) nullptr;
   }
 
+  // HACK: libc++ has a bug where it attempts to explicitly instantiate the
+  // functions
+  //     valarray<size_t>::valarray(size_t) and
+  //     valarray<size_t>::~valarray()
+  // that it declared to have internal linkage with the internal_linkage
+  // attribute. Ignore the explicit instantiation declaration in this case.
+  if (Specialization->hasAttr<InternalLinkageAttr>() &&
+      TSK == TSK_ExplicitInstantiationDeclaration) {
+    if (auto *RD = dyn_cast<CXXRecordDecl>(Specialization->getDeclContext()))
+      if (RD->getIdentifier() && RD->getIdentifier()->isStr("valarray") &&
+          RD->isInStdNamespace())
+        return (Decl*) nullptr;
+  }
+
   ProcessDeclAttributeList(S, Specialization, D.getDeclSpec().getAttributes());
 
   // In MSVC mode, dllimported explicit instantiation definitions are treated as
@@ -9444,11 +9470,11 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
          diag::ext_explicit_instantiation_without_qualified_id)
     << Specialization << D.getCXXScopeSpec().getRange();
 
-  CheckExplicitInstantiationScope(*this,
-                   FunTmpl? (NamedDecl *)FunTmpl
-                          : Specialization->getInstantiatedFromMemberFunction(),
-                                  D.getIdentifierLoc(),
-                                  D.getCXXScopeSpec().isSet());
+  CheckExplicitInstantiation(
+      *this,
+      FunTmpl ? (NamedDecl *)FunTmpl
+              : Specialization->getInstantiatedFromMemberFunction(),
+      D.getIdentifierLoc(), D.getCXXScopeSpec().isSet(), TSK);
 
   // FIXME: Create some kind of ExplicitInstantiationDecl here.
   return (Decl*) nullptr;

diff --git a/test/CXX/drs/dr0xx.cpp b/test/CXX/drs/dr0xx.cpp
index 911aab1747420240f55cdd2b8a97ad7976711728..53bd6f3f0538271522fb2805cae1eec4ed73d8b9 100644 (file)
--- a/test/CXX/drs/dr0xx.cpp
+++ b/test/CXX/drs/dr0xx.cpp
@@ -869,18 +869,17 @@ namespace dr68 { // dr68: yes
 }
 
 namespace dr69 { // dr69: yes
-  template<typename T> static void f() {}
+  template<typename T> static void f() {} // #dr69-f
   // FIXME: Should we warn here?
   inline void g() { f<int>(); }
-  // FIXME: This should be rejected, per [temp.explicit]p11.
-  extern template void f<char>();
+  extern template void f<char>(); // expected-error {{explicit instantiation declaration of 'f' with internal linkage}}
 #if __cplusplus < 201103L
   // expected-error@-2 {{C++11 extension}}
 #endif
   template<void(*)()> struct Q {};
   Q<&f<int> > q;
 #if __cplusplus < 201103L
-  // expected-error@-2 {{internal linkage}} expected-note@-11 {{here}}
+  // expected-error@-2 {{internal linkage}} expected-note@#dr69-f {{here}}
 #endif
 }
 

diff --git a/test/SemaCXX/PR10177.cpp b/test/SemaCXX/PR10177.cpp
index 59630be508859e600f8b88ac6f6d098a6dbebf29..0d2e792f5227f6352b1c0572a4aefd59ae3f44cd 100644 (file)
--- a/test/SemaCXX/PR10177.cpp
+++ b/test/SemaCXX/PR10177.cpp
@@ -57,11 +57,10 @@ namespace N {
 }
 
 #else
-// expected-no-diagnostics
 
 namespace { template<typename> extern int n; }
 template<typename T> int g() { return n<int>; }
-namespace { extern template int n<int>; }
+namespace { extern template int n<int>; } // expected-error {{explicit instantiation declaration of 'n<int>' with internal linkage}}
 
 #endif
 

diff --git a/test/SemaCXX/libcxx_valarray_hack.cpp b/test/SemaCXX/libcxx_valarray_hack.cpp
new file mode 100644 (file)
index 0000000..03dc573
--- /dev/null
+++ b/test/SemaCXX/libcxx_valarray_hack.cpp
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++11 -verify
+
+// This is a test for a hack in Clang that works around an issue with libc++'s
+// <valarray> implementation. The <valarray> header contains explicit
+// instantiations of functions that it declared with the internal_linkage
+// attribute, which are ill-formed by [temp.explicit]p13 (and meaningless).
+
+#ifdef BE_THE_HEADER
+
+#pragma GCC system_header
+namespace std {
+  using size_t = __SIZE_TYPE__;
+  template<typename T> struct valarray {
+    __attribute__((internal_linkage)) valarray(size_t) {}
+    __attribute__((internal_linkage)) ~valarray() {}
+  };
+
+  extern template valarray<size_t>::valarray(size_t);
+  extern template valarray<size_t>::~valarray();
+}
+
+#else
+
+#define BE_THE_HEADER
+#include "libcxx_valarray_hack.cpp"
+
+template<typename T> struct foo {
+  __attribute__((internal_linkage)) void x() {};
+};
+extern template void foo<int>::x(); // expected-error {{explicit instantiation declaration of 'x' with internal linkage}}
+
+#endif