Add a c2x language mode

[aaron.ballman]

Summary

This patch adds support for a "c2x" language standard mode for the eventual new C language standard, expected to come out in 202x. The spelling and capitalization is pulled from the C2x charter (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2021.htm).

I added a pretty simple driver test for this language mode because we do not currently have any C2x language features. However, I have a WIP patch that will require this functionality and figured that this part should be split off from it. If there is a better way to test this, or if it should wait for the WIP, please let me know.

[majnemer]

include/clang/Frontend/LangStandards.def

94

Should this be C2x instead of C2X?

[aaron.ballman]

include/clang/Frontend/LangStandards.def

94

Probably. :-D

[rsmith]

This seems premature; according to the charter, we are more than three years away from the C2x committee draft phase. Perhaps we should wait until we have either a new working draft or a paper approved by the WG14 for such a working draft.

[aaron.ballman]

In D23453#515816, @rsmith wrote:

This seems premature; according to the charter, we are more than three years away from the C2x committee draft phase. Perhaps we should wait until we have either a new working draft or a paper approved by the WG14 for such a working draft.

The problem is: I think I need the flag for working on some features that are being proposed, as WG14 does not typically accept novel language features. Specifically, I am planning work on N2049, adding attributes to C. This work will be done under a separate flag anyway (since it's obviously not approved and in the working draft), but I would like the feature to only be enabled for C2x and not C11 or earlier (at least initially) so that I don't have to worry about someone turning on the feature flag for C11 and running into a situation later where we don't want the feature supported in C11 (not that I have such a situation in mind currently). This is not entirely unlike how we don't support C++-style attributes in C++03 mode.

include/clang/Basic/LangOptions.def

 // FIXME: A lot of the BENIGN_ options should be COMPATIBLE_ instead.
 LANGOPT(C99               , 1, 0, "C99")
 LANGOPT(C11               , 1, 0, "C11")
+LANGOPT(C2x               , 1, 0, "C2x")
 LANGOPT(MSVCCompat        , 1, 0, "Microsoft Visual C++ full compatibility mode")
 LANGOPT(MicrosoftExt      , 1, 0, "Microsoft C++ extensions")
 LANGOPT(AsmBlocks         , 1, 0, "Microsoft inline asm blocks")

include/clang/Frontend/LangStandard.h

   C89 = (1 << 1),
   C99 = (1 << 2),
   C11 = (1 << 3),
-  CPlusPlus = (1 << 4),
-  CPlusPlus11 = (1 << 5),
-  CPlusPlus14 = (1 << 6),
-  CPlusPlus1z = (1 << 7),
-  Digraphs = (1 << 8),
-  GNUMode = (1 << 9),
-  HexFloat = (1 << 10),
-  ImplicitInt = (1 << 11)
+  C2x = (1 << 4),
+  CPlusPlus = (1 << 5),
+  CPlusPlus11 = (1 << 6),
+  CPlusPlus14 = (1 << 7),
+  CPlusPlus1z = (1 << 8),
+  Digraphs = (1 << 9),
+  GNUMode = (1 << 10),
+  HexFloat = (1 << 11),
+  ImplicitInt = (1 << 12)
 };
 
 }

   /// isC11 - Language is a superset of C11.
   bool isC11() const { return Flags & frontend::C11; }
 
+  /// isC2x - Language is a superset of C2x.
+  bool isC2x() const { return Flags & frontend::C2x; }
+
   /// isCPlusPlus - Language is a C++ variant.
   bool isCPlusPlus() const { return Flags & frontend::CPlusPlus; }
 

include/clang/Frontend/LangStandards.def

              "ISO C 2011 with GNU extensions",
              LineComment | C99 | C11 | Digraphs | GNUMode | HexFloat)
 
+// C2X modes
+LANGSTANDARD(c2x, "c2x",
+             "Working draft for ISO C 202x",
+             LineComment | C99 | C11 | C2x | Digraphs | HexFloat)
+
 // C++ modes
 LANGSTANDARD(cxx98, "c++98",
              "ISO C++ 1998 with amendments",

lib/Frontend/CompilerInvocation.cpp

   Opts.LineComment = Std.hasLineComments();
   Opts.C99 = Std.isC99();
   Opts.C11 = Std.isC11();
+  Opts.C2x = Std.isC2x();
   Opts.CPlusPlus = Std.isCPlusPlus();
   Opts.CPlusPlus11 = Std.isCPlusPlus11();
   Opts.CPlusPlus14 = Std.isCPlusPlus14();

test/Driver/clang_std_c.c

+/* Test various -std driver options for C. */
+// RUN: %clang -std=c11 -fsyntax-only %s 2>&1 | FileCheck %s
+// RUN: %clang -std=c2x -fsyntax-only %s 2>&1 | FileCheck %s
+
+// CHECK-NOT: invalid value 'c11' in '-std=c11'
+// CHECK-NOT: invalid value 'c2x' in '-std=c2x'
+