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

2 files changed, 24 insertions, 6 deletions

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 3156e35..0f263f7 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,8 @@
+2019-10-02  Joseph Myers  <joseph@codesourcery.com>
+
+	* c-parser.c (c_parser_asm_statement): Handle CPP_SCOPE like two
+	CPP_COLON tokens.
+
 2019-10-01  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* c-objc-common.c (useful_aka_type_p): New function.
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index c8afab2..6957297 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -6411,7 +6411,9 @@ c_parser_for_statement (c_parser *parser, bool ivdep, unsigned short unroll,
 
    The form with asm-goto-operands is valid if and only if the
    asm-qualifier-list contains goto, and is the only allowed form in that case.
-   Duplicate asm-qualifiers are not allowed.  */
+   Duplicate asm-qualifiers are not allowed.
+
+   The :: token is considered equivalent to two consecutive : tokens.  */
 
 static tree
 c_parser_asm_statement (c_parser *parser)
@@ -6509,17 +6511,28 @@ c_parser_asm_statement (c_parser *parser)
   nsections = 3 + is_goto;
   for (section = 0; section < nsections; ++section)
     {
-      if (!c_parser_require (parser, CPP_COLON,
-			     is_goto
-			     ? G_("expected %<:%>")
-			     : G_("expected %<:%> or %<)%>"),
-			     UNKNOWN_LOCATION, is_goto))
+      if (c_parser_next_token_is (parser, CPP_SCOPE))
+	{
+	  ++section;
+	  if (section == nsections)
+	    {
+	      c_parser_error (parser, "expected %<)%>");
+	      goto error_close_paren;
+	    }
+	  c_parser_consume_token (parser);
+	}
+      else if (!c_parser_require (parser, CPP_COLON,
+				  is_goto
+				  ? G_("expected %<:%>")
+				  : G_("expected %<:%> or %<)%>"),
+				  UNKNOWN_LOCATION, is_goto))
 	goto error_close_paren;
 
       /* Once past any colon, we're no longer a simple asm.  */
       simple = false;
 
       if ((!c_parser_next_token_is (parser, CPP_COLON)
+	   && !c_parser_next_token_is (parser, CPP_SCOPE)
 	   && !c_parser_next_token_is (parser, CPP_CLOSE_PAREN))
 	  || section == 3)
 	switch (section)