glr2.cc: require C++11

Reported by Dagobert Michelsen.
https://lists.gnu.org/r/bug-bison/2021-08/msg00006.html

* m4/bison-cxx-std.m4 (_BISON_CXXSTD_98_snippet): We don't need
vector::data, it was only for glr2.cc, which is C++11 anyway.
(_BISON_CXXSTD_11_snippet): We need vector::data and std::swap on
arrays.
* m4/cxx.m4 (BISON_TEST_FOR_WORKING_CXX_COMPILER): We don't need
vector::data.
* tests/local.at (AT_COMPILE_CXX): Skip when glr2.cc and no support
for C++11.

TODO

@@ -1,3 +1,6 @@
+* 3.8
+Don't showcase multi start.
+
 * Soon
 ** scan-code
 The default case is scanning char-per-char.
@@ -183,7 +186,7 @@ Les catégories d'avertissements incluent :
 
 Line -1 and -3 should mention CATEGORIE, not CATEGORY.
 
-* Bison 3.8
+* Bison 3.9
 ** Rewrite glr.cc (currently glr2.cc)
 *** custom error messages
 

data/skeletons/glr2.cc

@@ -1370,7 +1370,6 @@ public:
     check_ ();
     other.check_ ();]])[
     std::swap (is_state_, other.is_state_);
-    // NB: swap on arrays is C++11.
     std::swap (raw_, other.raw_);
     return *this;
   }

m4/bison-cxx-std.m4

@@ -7,36 +7,22 @@
 # with or without modifications, as long as this notice is preserved.
 
 m4_define([_BISON_CXXSTD_98_snippet],
-[[#include <cassert>
-#include <vector>
-
-void cxx98_vector ()
-{
-  typedef std::vector<int> ints;
-
-  // Check support for std::vector<T,Allocator>::data.
-  // GCC 4.2 on macOS claims to support C++98, but does not feature it.
-  //
-  // input.cc: In member function 'void state_stack::yycompressStack()':
-  // input.cc:1774: error: 'class std::vector<glr_stack_item, std::allocator<glr_stack_item> >' has no member named 'data'
-  //
-  // <https://trac.macports.org/raw-attachment/ticket/59927/bison-test-results-20210811-95b72.log.xz>.
-  ints my_ints;
-  assert (my_ints.data () == &my_ints[0]);
-}
-]])
+[[]])
 
 m4_define([_BISON_CXXSTD_03_snippet],
-[])
+[[]])
 
 m4_define([_BISON_CXXSTD_11_snippet],
-[[#include <algorithm>
+[[  // C++11
+#include <algorithm>
+#include <cassert>
 #include <memory>
 #include <set>
 #include <sstream>
 #include <string>
+#include <utility> // std::swap
+#include <vector>
 
-  // C++11
   template <typename T>
   struct check
   {
@@ -80,6 +66,22 @@ m4_define([_BISON_CXXSTD_11_snippet],
 
   // GCC 4.8.2 on Solaris 11.3 does not support to_string.
   auto e = std::to_string(42);
+
+  // Needed by glr2.cc.
+  void cxx11_vector_data ()
+  {
+    std::vector<int> ints;
+    ints.emplace_back (42);
+    assert (ints.data () == &ints[0]);
+  }
+
+  // Needed by glr2.cc.
+  void cxx11_array_swap ()
+  {
+    int i0[4] = { 1, 2, 3, 4 };
+    int i1[4] = { 5, 6, 7, 8 };
+    std::swap (i0, i1);
+  }
 ]])
 
 m4_define([_BISON_CXXSTD_14_snippet],
@@ -177,7 +179,7 @@ m4_define([_BISON_CXXSTD_testbody],
 
 # BISON_CXXSTD(STD)
 # -----------------
-# Check whether the C++ compiler support STD (11, 98, 2b, etc.).
+# Check whether the C++ compiler supports STD (11, 98, 2b, etc.).
 # If it does, AC_SUBST 'CXX<STD>_CXXFLAGS' to the corresponding flags.
 AC_DEFUN([BISON_CXXSTD],
 [AC_REQUIRE([AC_PROG_CXX])

m4/cxx.m4

@@ -28,17 +28,13 @@ AC_DEFUN([BISON_TEST_FOR_WORKING_CXX_COMPILER],
     AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM(
          [[
-          #include <cassert>
           #include <cstdlib>
           #include <iostream>
           #include <map>
           #include <string>
-          #include <vector>
           using namespace std;]],
          [[std::cerr << "";
           cout << "";
-          std::vector<int> ints;
-          assert(ints.data () == &ints[0]);
           typedef std::pair<unsigned, int> uipair;
           std::map<unsigned, int> m;
           std::map<unsigned, int>::iterator i;

tests/local.at

@@ -1362,8 +1362,10 @@ AT_CHECK(m4_join([ ],
 # otherwise pass "-c"; this is a hack.  The default SOURCES is OUTPUT
 # with trailing ".o" removed, and ".cc" appended.
 m4_define([AT_COMPILE_CXX],
-[AT_KEYWORDS(c++)
+[AT_KEYWORDS([c++])
 AT_SKIP_IF([[! $BISON_CXX_WORKS]])
+m4_ifdef([AT_GLR2_CC_IF],
+  [AT_GLR2_CC_IF([AT_SKIP_IF([[test x"$CXX11_CXXFLAGS" == x]])])])
 AT_CHECK(m4_join([ ],
                  [$CXX $CXXFLAGS $CPPFLAGS $3],
                  [m4_bmatch([$1], [[.]], [-c], [$LDFLAGS])],

tests/output.at

@@ -744,6 +744,7 @@ m4_popdef([AT_TEST])
 AT_SETUP([C++ Output File Prefix Mapping])
 
 # AT_TEST([PREFIX], [DIRECTIVES])
+# -------------------------------
 m4_pushdef([AT_TEST],
 [AT_BISON_OPTION_PUSHDEFS([%skeleton "lalr1.cc" %define api.namespace {$1} $2])
 AT_LOC_PUSHDEF([begin.line], [begin.column], [end.line], [end.column])