[PATCH 5/9] build: reject C++ compilers that don't support std::vector::data

[Akim Demaille]

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'

Reported by Christopher Nielsen <mascguy@github.com>.
<https://trac.macports.org/raw-attachment/ticket/59927/bison-test-results-20210811-95b72.log.xz>.

* m4/bison-cxx-std.m4 (_BISON_CXXSTD_98_snippet): Check for it.
* m4/cxx.m4 (BISON_TEST_FOR_WORKING_CXX_COMPILER): Ditto.
---
 m4/bison-cxx-std.m4 | 15 ++++++++++++++-
 m4/cxx.m4           | 13 +++++++++----
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/m4/bison-cxx-std.m4 b/m4/bison-cxx-std.m4
index 65d59cc7..4a71d20f 100644
--- a/m4/bison-cxx-std.m4
+++ b/m4/bison-cxx-std.m4
@@ -10,7 +10,20 @@ m4_define([_BISON_CXXSTD_98_snippet],
 [[#include <cassert>
 #include <vector>
 
-typedef std::vector<int> ints;
+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],
diff --git a/m4/cxx.m4 b/m4/cxx.m4
index 36e66c43..0a99fa27 100644
--- a/m4/cxx.m4
+++ b/m4/cxx.m4
@@ -27,20 +27,25 @@ AC_DEFUN([BISON_TEST_FOR_WORKING_CXX_COMPILER],
     bison_cv_cxx_works=no
     AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM(
-         [#include <cstdlib>
+         [[
+          #include <cassert>
+          #include <cstdlib>
           #include <iostream>
           #include <map>
           #include <string>
-          using namespace std;],
-         [std::cerr << "";
+          #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;
           m.insert (uipair (4, -4));
           for (i = m.begin (); i != m.end (); ++i)
             if (i->first != 4)
-              return 1;])],
+              return 1;]])],
       [AS_IF([AC_TRY_COMMAND([$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS 
$LDFLAGS conftest.$ac_objext $LIBS >&AS_MESSAGE_LOG_FD])],
          [AS_IF([test "$cross_compiling" = yes],
             [bison_cv_cxx_works=cross],
-- 
2.32.0