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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@291382 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 47c1af9ad3a0b77d0d7252d4001bfa6310e447f8..02b73e9113fa9e343eb4e03a786f2c22a008e406 100644 (file)
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -9135,6 +9135,16 @@ NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
   // 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>(

diff --git a/test/SemaCXX/libstdcxx_gets_hack.cpp b/test/SemaCXX/libstdcxx_gets_hack.cpp
new file mode 100644 (file)
index 0000000..0d915d0
--- /dev/null
+++ b/test/SemaCXX/libstdcxx_gets_hack.cpp
@@ -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