Handle :: tokens in C for C2x.

As part of adding [[]]-style attributes, C2x adds the token :: for use
in scoped attribute names.

This patch adds corresponding support for that token in C to GCC.  The
token is supported both for C2x and for older gnu* standards (on the
basis that extensions are normally supported in older gnu* versions;
people will expect to be able to use [[]] attributes, before C2x is
the default, without needing to use -std=gnu2x).

There are no cases in older C standards where the token : can be
followed by a token starting with : in syntactically valid sources;
the only cases the :: token could break in older standard C thus are
ones involving concatenation of pp-tokens where the result does not
end up as tokens (e.g., gets stringized).  In GNU C extensions, the
main case where :: might appear in existing sources is in asm
statements, and the C parser is thus made to handle it like two
consecutive : tokens, which the C++ parser already does.  A limited
test of various positionings of :: in asm statements is added to the
testsuite (in particular, to cover the syntax error when :: means too
many colons but a single : would be OK), but existing tests cover a
variety of styles there anyway.

Technically there are cases in Objective-C and OpenMP for which this
also changes how previously valid code is lexed: the objc-selector-arg
syntax allows multiple consecutive : tokens (although I don't think
they are particularly useful there), while OpenMP syntax includes
array section syntax such as [:] which, before :: was a token, could
also be written as [::> (there might be other OpenMP cases potentially
affected, I didn't check all the OpenMP syntax in detail).  I don't
think either of those cases affects the basis for supporting the ::
token in all -std=gnu* modes, or that there is any obvious need to
special-case handling of CPP_SCOPE tokens for those constructs the way
there is for asm statements.

cpp_avoid_paste, which determines when spaces need adding between
tokens in preprocessed output where there wouldn't otherwise be
whitespace between them (e.g. if stringized), already inserts space
between : and : unconditionally, rather than only for C++, so no
change is needed there (but a C2x test is added that such space is
indeed inserted).

Bootstrapped with no regressions on x86-64-pc-linux-gnu.

gcc/c:
	* c-parser.c (c_parser_asm_statement): Handle CPP_SCOPE like two
	CPP_COLON tokens.

gcc/testsuite:
	* gcc.dg/asm-scope-1.c, gcc.dg/cpp/c11-scope-1.c,
	gcc.dg/cpp/c17-scope-1.c, gcc.dg/cpp/c2x-scope-1.c,
	gcc.dg/cpp/c2x-scope-2.c, gcc.dg/cpp/c90-scope-1.c,
	gcc.dg/cpp/c94-scope-1.c, gcc.dg/cpp/c99-scope-1.c,
	gcc.dg/cpp/gnu11-scope-1.c, gcc.dg/cpp/gnu17-scope-1.c,
	gcc.dg/cpp/gnu89-scope-1.c, gcc.dg/cpp/gnu99-scope-1.c: New tests.

libcpp:
	* include/cpplib.h (struct cpp_options): Add member scope.
	* init.c (struct lang_flags, lang_defaults): Likewise.
	(cpp_set_lang): Set scope member of pfile.
	* lex.c (_cpp_lex_direct): Test CPP_OPTION (pfile, scope) not
	CPP_OPTION (pfile, cplusplus) for creating CPP_SCOPE tokens.

From-SVN: r276434

4 files changed, 37 insertions, 24 deletions

diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 1ca622df6fd..682caaccd96 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,11 @@
+2019-10-02  Joseph Myers  <joseph@codesourcery.com>
+
+	* include/cpplib.h (struct cpp_options): Add member scope.
+	* init.c (struct lang_flags, lang_defaults): Likewise.
+	(cpp_set_lang): Set scope member of pfile.
+	* lex.c (_cpp_lex_direct): Test CPP_OPTION (pfile, scope) not
+	CPP_OPTION (pfile, cplusplus) for creating CPP_SCOPE tokens.
+
 2019-09-26  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* charset.c (UCS_LIMIT): New macro.
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index a645f8136a6..ccbcfde6dc4 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -483,6 +483,9 @@ struct cpp_options
   /* Nonzero for C++2a __VA_OPT__ feature.  */
   unsigned char va_opt;
 
+  /* Nonzero for the '::' token.  */
+  unsigned char scope;
+
   /* Holds the name of the target (execution) character set.  */
   const char *narrow_charset;
 
diff --git a/libcpp/init.c b/libcpp/init.c
index ccbfc96489d..c932598b5fb 100644
--- a/libcpp/init.c
+++ b/libcpp/init.c
@@ -92,32 +92,33 @@ struct lang_flags
   char trigraphs;
   char utf8_char_literals;
   char va_opt;
+  char scope;
 };
 
 static const struct lang_flags lang_defaults[] =
-{ /*              c99 c++ xnum xid c11 std digr ulit rlit udlit bincst digsep trig u8chlit vaopt */
-  /* GNUC89   */  { 0,  0,  1,  0,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1 },
-  /* GNUC99   */  { 1,  0,  1,  1,  0,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1 },
-  /* GNUC11   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1 },
-  /* GNUC17   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1 },
-  /* GNUC2X   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1 },
-  /* STDC89   */  { 0,  0,  0,  0,  0,  1,  0,   0,   0,   0,    0,     0,     1,   0,      0 },
-  /* STDC94   */  { 0,  0,  0,  0,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0 },
-  /* STDC99   */  { 1,  0,  1,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0 },
-  /* STDC11   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0 },
-  /* STDC17   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0 },
-  /* STDC2X   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0 },
-  /* GNUCXX   */  { 0,  1,  1,  1,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1 },
-  /* CXX98    */  { 0,  1,  0,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0 },
-  /* GNUCXX11 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    0,     0,     0,   0,      1 },
-  /* CXX11    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    0,     0,     1,   0,      0 },
-  /* GNUCXX14 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   0,      1 },
-  /* CXX14    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    1,     1,     1,   0,      0 },
-  /* GNUCXX17 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1 },
-  /* CXX17    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      0 },
-  /* GNUCXX2A */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1 },
-  /* CXX2A    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1 },
-  /* ASM      */  { 0,  0,  1,  0,  0,  0,  0,   0,   0,   0,    0,     0,     0,   0,      0 }
+{ /*              c99 c++ xnum xid c11 std digr ulit rlit udlit bincst digsep trig u8chlit vaopt scope*/
+  /* GNUC89   */  { 0,  0,  1,  0,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1 },
+  /* GNUC99   */  { 1,  0,  1,  1,  0,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1 },
+  /* GNUC11   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1 },
+  /* GNUC17   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1 },
+  /* GNUC2X   */  { 1,  0,  1,  1,  1,  0,  1,   1,   1,   0,    0,     0,     0,   0,      1,   1 },
+  /* STDC89   */  { 0,  0,  0,  0,  0,  1,  0,   0,   0,   0,    0,     0,     1,   0,      0,   0 },
+  /* STDC94   */  { 0,  0,  0,  0,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0 },
+  /* STDC99   */  { 1,  0,  1,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   0 },
+  /* STDC11   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0 },
+  /* STDC17   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   0 },
+  /* STDC2X   */  { 1,  0,  1,  1,  1,  1,  1,   1,   0,   0,    0,     0,     1,   0,      0,   1 },
+  /* GNUCXX   */  { 0,  1,  1,  1,  0,  0,  1,   0,   0,   0,    0,     0,     0,   0,      1,   1 },
+  /* CXX98    */  { 0,  1,  0,  1,  0,  1,  1,   0,   0,   0,    0,     0,     1,   0,      0,   1 },
+  /* GNUCXX11 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    0,     0,     0,   0,      1,   1 },
+  /* CXX11    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    0,     0,     1,   0,      0,   1 },
+  /* GNUCXX14 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   0,      1,   1 },
+  /* CXX14    */  { 1,  1,  0,  1,  1,  1,  1,   1,   1,   1,    1,     1,     1,   0,      0,   1 },
+  /* GNUCXX17 */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1 },
+  /* CXX17    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      0,   1 },
+  /* GNUCXX2A */  { 1,  1,  1,  1,  1,  0,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1 },
+  /* CXX2A    */  { 1,  1,  1,  1,  1,  1,  1,   1,   1,   1,    1,     1,     0,   1,      1,   1 },
+  /* ASM      */  { 0,  0,  1,  0,  0,  0,  0,   0,   0,   0,    0,     0,     0,   0,      0,   0 }
 };
 
 /* Sets internal flags correctly for a given language.  */
@@ -143,6 +144,7 @@ cpp_set_lang (cpp_reader *pfile, enum c_lang lang)
   CPP_OPTION (pfile, trigraphs)			 = l->trigraphs;
   CPP_OPTION (pfile, utf8_char_literals)	 = l->utf8_char_literals;
   CPP_OPTION (pfile, va_opt)			 = l->va_opt;
+  CPP_OPTION (pfile, scope)			 = l->scope;
 }
 
 /* Initialize library global state.  */
diff --git a/libcpp/lex.c b/libcpp/lex.c
index 0e8de3807b3..3e7d1c37ff5 100644
--- a/libcpp/lex.c
+++ b/libcpp/lex.c
@@ -3104,7 +3104,7 @@ _cpp_lex_direct (cpp_reader *pfile)
 
     case ':':
       result->type = CPP_COLON;
-      if (*buffer->cur == ':' && CPP_OPTION (pfile, cplusplus))
+      if (*buffer->cur == ':' && CPP_OPTION (pfile, scope))
 	buffer->cur++, result->type = CPP_SCOPE;
       else if (*buffer->cur == '>' && CPP_OPTION (pfile, digraphs))
 	{