Disentangle HAVE__BOOL from ac_cv_header_stdbool_h.

AC_CHECK_HEADER_STDBOOL is documented to make two checks: whether the
C99 header <stdbool.h> is available and fulfills its
specification (i.e. including it makes the type ‘bool’ and the
constants ‘true’ and ‘false’ available), and, independently, whether
the type ‘_Bool’ is available.

In C++, the type ‘_Bool’ is usually _not_ available, but <stdbool.h>
is still supposed to be include-able and the type ‘bool’ and the
constants ‘true’ and ‘false’ are still supposed to be available
(unconditionally).  However, the test for <stdbool.h> fulfilling its
specification freely used _Bool, and would therefore fail spuriously.
Correct this by checking for _Bool first, and then refactoring the
test program for <stdbool.h> so that it does all its tests using bool,
then repeats them with _Bool only when available.

* lib/autoconf/headers.m4 (AC_CHECK_HEADER_STDBOOL): Do the test for
  _Bool before the test for stdbool.h.  Test semantics of bool
  unconditionally; test _Bool only when HAVE__BOOL is defined.

1 files changed, 89 insertions, 45 deletions

diff --git a/lib/autoconf/headers.m4 b/lib/autoconf/headers.m4
index 3b97a185..17a5abac 100644
--- a/lib/autoconf/headers.m4
+++ b/lib/autoconf/headers.m4
@@ -574,70 +574,114 @@ AN_IDENTIFIER([bool], [AC_CHECK_HEADER_STDBOOL])
 AN_IDENTIFIER([true], [AC_CHECK_HEADER_STDBOOL])
 AN_IDENTIFIER([false],[AC_CHECK_HEADER_STDBOOL])
 AC_DEFUN([AC_CHECK_HEADER_STDBOOL],
-  [AC_CACHE_CHECK([for stdbool.h that conforms to C99],
+  [AC_CHECK_TYPES([_Bool])
+   AC_CACHE_CHECK([for stdbool.h that conforms to C99],
      [ac_cv_header_stdbool_h],
      [AC_COMPILE_IFELSE(
         [AC_LANG_PROGRAM(
-           [[
-             #include <stdbool.h>
+           [[#include <stdbool.h>
+
+             #ifndef __bool_true_false_are_defined
+               #error "__bool_true_false_are_defined is not defined"
+             #endif
+             char a[__bool_true_false_are_defined == 1 ? 1 : -1];
+
+             /* Regardless of whether this is C++ or "_Bool" is a
+                valid type name, "true" and "false" should be usable
+                in #if expressions and integer constant expressions,
+                and "bool" should be a valid type name.  */
+
+             #if !true
+               #error "'true' is not true"
+             #endif
+             #if true != 1
+               #error "'true' is not equal to 1"
+             #endif
+             char b[true == 1 ? 1 : -1];
+             char c[true];
+
+             #if false
+               #error "'false' is not false"
+             #endif
+             #if false != 0
+               #error "'false' is not equal to 0"
+             #endif
+             char d[false == 0 ? 1 : -1];
+
+             enum { e = false, f = true, g = false * true, h = true * 256 };
+
+             char i[(bool) 0.5 == true ? 1 : -1];
+             char j[(bool) 0.0 == false ? 1 : -1];
+             char k[sizeof (bool) > 0 ? 1 : -1];
+
+             struct sb { bool s: 1; bool t; } s;
+             char l[sizeof s.t > 0 ? 1 : -1];
+
+             /* The following fails for
+                HP aC++/ANSI C B3910B A.05.55 [Dec 04 2003]. */
+             bool m[h];
+             char n[sizeof m == h * sizeof m[0] ? 1 : -1];
+             char o[-1 - (bool) 0 < 0 ? 1 : -1];
+             /* Catch a bug in an HP-UX C compiler.  See
+         https://gcc.gnu.org/ml/gcc-patches/2003-12/msg02303.html
+         https://lists.gnu.org/archive/html/bug-coreutils/2005-11/msg00161.html
+              */
+             bool p = true;
+             bool *pp = &p;
 
+             /* C 1999 specifies that bool, true, and false are to be
+                macros, but C++ 2011 and later overrule this.  */
              #if __cplusplus < 201103
               #ifndef bool
-               "error: bool is not defined"
+               #error "bool is not defined"
               #endif
               #ifndef false
-               "error: false is not defined"
-              #endif
-              #if false
-               "error: false is not 0"
+               #error "false is not defined"
               #endif
               #ifndef true
-               "error: true is not defined"
-              #endif
-              #if true != 1
-               "error: true is not 1"
+               #error "true is not defined"
               #endif
              #endif
 
-             #ifndef __bool_true_false_are_defined
-              "error: __bool_true_false_are_defined is not defined"
+             /* If _Bool is available, repeat with it all the tests
+                above that used bool.  */
+             #ifdef HAVE__BOOL
+               struct sB { _Bool s: 1; _Bool t; } t;
+
+               char q[(_Bool) 0.5 == true ? 1 : -1];
+               char r[(_Bool) 0.0 == false ? 1 : -1];
+               char u[sizeof (_Bool) > 0 ? 1 : -1];
+               char v[sizeof t.t > 0 ? 1 : -1];
+
+               _Bool w[h];
+               char x[sizeof m == h * sizeof m[0] ? 1 : -1];
+               char y[-1 - (_Bool) 0 < 0 ? 1 : -1];
+               _Bool z = true;
+               _Bool *pz = &p;
              #endif
-
-             struct s { _Bool s: 1; _Bool t; } s;
-
-             char a[true == 1 ? 1 : -1];
-             char b[false == 0 ? 1 : -1];
-             char c[__bool_true_false_are_defined == 1 ? 1 : -1];
-             char d[(bool) 0.5 == true ? 1 : -1];
-             /* See body of main program for 'e'.  */
-             char f[(_Bool) 0.0 == false ? 1 : -1];
-             char g[true];
-             char h[sizeof (_Bool)];
-             char i[sizeof s.t];
-             enum { j = false, k = true, l = false * true, m = true * 256 };
-             /* The following fails for
-                HP aC++/ANSI C B3910B A.05.55 [Dec 04 2003]. */
-             _Bool n[m];
-             char o[sizeof n == m * sizeof n[0] ? 1 : -1];
-             char p[-1 - (_Bool) 0 < 0 && -1 - (bool) 0 < 0 ? 1 : -1];
-             /* Catch a bug in an HP-UX C compiler.  See
-                https://gcc.gnu.org/ml/gcc-patches/2003-12/msg02303.html
-                https://lists.gnu.org/archive/html/bug-coreutils/2005-11/msg00161.html
-              */
-             _Bool q = true;
-             _Bool *pq = &q;
            ]],
            [[
-             bool e = &s;
-             *pq |= q;
-             *pq |= ! q;
-             /* Refer to every declared value, to avoid compiler optimizations.  */
-             return (!a + !b + !c + !d + !e + !f + !g + !h + !i + !!j + !k + !!l
-                     + !m + !n + !o + !p + !q + !pq);
+             bool ps = &s;
+             *pp |= p;
+             *pp |= ! p;
+
+             #ifdef HAVE__BOOL
+               _Bool pt = &t;
+               *pz |= z;
+               *pz |= ! z;
+             #endif
+
+             /* Refer to every declared value, so they cannot be
+                discarded as unused.  */
+             return (!a + !b + !c + !d + !e + !f + !g + !h + !i + !j + !k
+                     + !l + !m + !n + !o + !p + !pp + !ps
+             #ifdef HAVE__BOOL
+                     + !q + !r + !u + !v + !w + !x + !y + !z + !pt
+             #endif
+                    );
            ]])],
         [ac_cv_header_stdbool_h=yes],
         [ac_cv_header_stdbool_h=no])])
-   AC_CHECK_TYPES([_Bool])
 ])# AC_CHECK_HEADER_STDBOOL