r291382 - PR18402: work around bug in libstdc++4.8's detection of whether ::gets exists.

[Richard Smith via cfe-commits]

Author: rsmith
Date: Sat Jan  7 22:01:15 2017
New Revision: 291382

URL: http://llvm.org/viewvc/llvm-project?rev=291382&view=rev
Log:
PR18402: work around bug in libstdc++4.8's detection of whether ::gets exists.

This should allow clang to successfully compile libstdc++4.8's headers in C++14
mode.

Added:
    cfe/trunk/test/SemaCXX/libstdcxx_gets_hack.cpp
Modified:
    cfe/trunk/lib/Sema/SemaDeclCXX.cpp

Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=291382&r1=291381&r2=291382&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Sat Jan  7 22:01:15 2017
@@ -9135,6 +9135,16 @@ NamedDecl *Sema::BuildUsingDeclaration(S
   // invalid).
   if (R.empty() &&
       NameInfo.getName().getNameKind() != DeclarationName::CXXConstructorName) {
+    // HACK: Work around a bug in libstdc++'s detection of ::gets. Sometimes
+    // it will believe that glibc provides a ::gets in cases where it does not,
+    // and will try to pull it into namespace std with a using-declaration.
+    // Just ignore the using-declaration in that case.
+    auto *II = NameInfo.getName().getAsIdentifierInfo();
+    if (getLangOpts().CPlusPlus14 && II && II->isStr("gets") &&
+        CurContext->isStdNamespace() &&
+        isa<TranslationUnitDecl>(LookupContext) &&
+        getSourceManager().isInSystemHeader(UsingLoc))
+      return nullptr;
     if (TypoCorrection Corrected = CorrectTypo(
             R.getLookupNameInfo(), R.getLookupKind(), S, &SS,
             llvm::make_unique<UsingValidatorCCC>(

Added: cfe/trunk/test/SemaCXX/libstdcxx_gets_hack.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/libstdcxx_gets_hack.cpp?rev=291382&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/libstdcxx_gets_hack.cpp (added)
+++ cfe/trunk/test/SemaCXX/libstdcxx_gets_hack.cpp Sat Jan  7 22:01:15 2017
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -fsyntax-only %s -std=c++14 -verify
+
+// This is a test for an egregious hack in Clang that works around
+// an issue with libstdc++'s detection of whether glibc provides a
+// ::gets function. If there is no ::gets, ignore
+//   using ::gets;
+// in namespace std.
+//
+// See PR18402 and gcc.gnu.org/PR77795 for more details.
+
+#ifdef BE_THE_HEADER
+
+#pragma GCC system_header
+namespace std {
+  using ::gets;
+  using ::getx; // expected-error {{no member named 'getx'}}
+}
+
+#else
+
+#define BE_THE_HEADER
+#include "libstdcxx_pointer_return_false_hack.cpp"
+
+namespace foo {
+  using ::gets; // expected-error {{no member named 'gets'}}
+}
+
+#endif