Use an allow list on reserved macro identifiers

[serge-sans-paille]

Summary

The allow list is based on man feature_test_macros

This fixes https://bugs.llvm.org/show_bug.cgi?id=50248

[lebedev.ri]

There is a number of other macros that are meant to be user-defined,
see e.g. https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_macros.html

[lebedev.ri]

Also, cfe-commits not subscribed

[aaron.ballman]

Adding cfe-commits.

[aaron.ballman]

Some additional ones to allow from MSDN: _CRT_SECURE_NO_WARNINGS, _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES, _CRT_NONSTDC_NO_WARNINGS, (https://docs.microsoft.com/en-us/cpp/c-runtime-library/security-features-in-the-crt?view=msvc-160).

clang/lib/Lex/PPDirectives.cpp

125

[aaron.ballman]

clang/lib/Lex/PPDirectives.cpp

125

Can you add a comment that this list is required to remain in alphabetical order (due to the use of binary_search) and list the identifiers in long-form rather than columns of three (this makes it easier for folks inserting new elements into the list)?

[serge-sans-paille]

Minor nits as suggested by reviewers + extend the list.

[aaron.ballman]

LGTM!

clang/lib/Lex/PPDirectives.cpp

if (M->getTopLevelModule()->IsFramework && CurrentModule == ModuleName &&
       !CurrentModule.endswith("_Private") && TopLevelName.endswith("_Private"))
     TopLevelName = TopLevelName.drop_back(8);
 
   return TopLevelName == CurrentModule;
 }
 
 static MacroDiag shouldWarnOnMacroDef(Preprocessor &PP, IdentifierInfo *II) {
   const LangOptions &Lang = PP.getLangOpts();
-  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved)
+  if (II->isReserved(Lang) != ReservedIdentifierStatus::NotReserved) {
+    // list from:
+    // - https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_macros.html
+    // - https://docs.microsoft.com/en-us/cpp/c-runtime-library/security-features-in-the-crt?view=msvc-160
+    // - man 7 feature_test_macros
+    // The list must be sorted for correct binary search.
+    static constexpr StringRef ReservedMacro[] = {
+        "_ATFILE_SOURCE",
+        "_BSD_SOURCE",
+        "_CRT_NONSTDC_NO_WARNINGS",
+        "_CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES",
+        "_CRT_SECURE_NO_WARNINGS",
+        "_FILE_OFFSET_BITS",
+        "_FORTIFY_SOURCE",
+        "_GLIBCXX_ASSERTIONS",
+        "_GLIBCXX_CONCEPT_CHECKS",
+        "_GLIBCXX_DEBUG",
+        "_GLIBCXX_DEBUG_PEDANTIC",
+        "_GLIBCXX_PARALLEL",
+        "_GLIBCXX_PARALLEL_ASSERTIONS",
+        "_GLIBCXX_SANITIZE_VECTOR",
+        "_GLIBCXX_USE_CXX11_ABI",
+        "_GLIBCXX_USE_DEPRECATED",
+        "_GNU_SOURCE",
+        "_ISOC11_SOURCE",
+        "_ISOC95_SOURCE",
+        "_ISOC99_SOURCE",
+        "_LARGEFILE64_SOURCE",
+        "_POSIX_C_SOURCE",
+        "_REENTRANT",
+        "_SVID_SOURCE",
+        "_THREAD_SAFE",
+        "_XOPEN_SOURCE",
+        "_XOPEN_SOURCE_EXTENDED",
+        "__STDCPP_WANT_MATH_SPEC_FUNCS__",
+        "__STDC_FORMAT_MACROS",
+    };
+    if (std::binary_search(ReservedMacro.begin(), ReservedMacro.end(),
+                           II->getName()))
+      return MD_NoWarn;
+
     return MD_ReservedMacro;
+  }
   StringRef Text = II->getName();
   if (II->isKeyword(Lang))
     return MD_KeywordDef;
   if (Lang.CPlusPlus11 && (Text.equals("override") || Text.equals("final")))
     return MD_KeywordDef;
   return MD_NoWarn;
 }
 

clang/test/Preprocessor/macro-reserved.c

 
 #undef switch
 #undef final
 #undef __cplusplus // expected-warning {{macro name is a reserved identifier}}
 #undef _HAVE_X     // expected-warning {{macro name is a reserved identifier}}
 #undef X__Y
 
 int x;
+
+#define _GNU_SOURCE          // no-warning
+#define __STDC_FORMAT_MACROS // no-warning