Use stdbool.h if suitable

Using the standard bool type provided by C allows some recent compilers
and debuggers to give better diagnostics.  Also, some extension code and
third-party headers are increasingly pulling in stdbool.h, so it's
probably saner if everyone uses the same definition.

But PostgreSQL code is not prepared to handle bool of a size other than
1, so we keep our own old definition if we encounter a stdbool.h with a
bool of a different size.  (Among current build farm members, this only
applies to old macOS versions on PowerPC.)

To check that the used bool is of the right size, add a static
assertions about size of GinTernaryValue vs bool.  This is currently the
only place that assumes that bool and char are of the same size.

Discussion: https://www.postgresql.org/message-id/flat/3a0fe7e1-5ed1-414b-9230-53bbc0ed1f49@2ndquadrant.com

3 files changed, 23 insertions, 4 deletions

diff --git a/src/include/access/gin.h b/src/include/access/gin.h
index 0acdb88241e..3d8a130b69b 100644
--- a/src/include/access/gin.h
+++ b/src/include/access/gin.h
@@ -51,8 +51,8 @@ typedef struct GinStatsData
 /*
  * A ternary value used by tri-consistent functions.
  *
- * For convenience, this is compatible with booleans. A boolean can be
- * safely cast to a GinTernaryValue.
+ * This must be of the same size as a bool because some code will cast a
+ * pointer to a bool to a pointer to a GinTernaryValue.
  */
 typedef char GinTernaryValue;
 
diff --git a/src/include/c.h b/src/include/c.h
index 37c0c391990..107f4f6bcd7 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -255,12 +255,21 @@
  * bool
  *		Boolean value, either true or false.
  *
- * XXX for C++ compilers, we assume the compiler has a compatible
- * built-in definition of bool.
+ * Use stdbool.h if available and its bool has size 1.  That's useful for
+ * better compiler and debugger output and for compatibility with third-party
+ * libraries.  But PostgreSQL currently cannot deal with bool of other sizes;
+ * there are static assertions around the code to prevent that.
+ *
+ * For C++ compilers, we assume the compiler has a compatible built-in
+ * definition of bool.
  */
 
 #ifndef __cplusplus
 
+#if defined(HAVE_STDBOOL_H) && SIZEOF_BOOL == 1
+#include <stdbool.h>
+#else
+
 #ifndef bool
 typedef char bool;
 #endif
@@ -273,6 +282,7 @@ typedef char bool;
 #define false	((bool) 0)
 #endif
 
+#endif
 #endif							/* not C++ */
 
 
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index e934cf87bd2..b0477f02311 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -356,6 +356,9 @@
 /* Define to 1 if you have the `SSL_get_current_compression' function. */
 #define HAVE_SSL_GET_CURRENT_COMPRESSION 1
 
+/* Define to 1 if stdbool.h conforms to C99. */
+/* #undef HAVE_STDBOOL_H */
+
 /* Define to 1 if you have the <stdint.h> header file. */
 /* #undef HAVE_STDINT_H */
 
@@ -524,6 +527,9 @@
 /* Define to 1 if you have the <winldap.h> header file. */
 /* #undef HAVE_WINLDAP_H */
 
+/* Define to 1 if the system has the type `_Bool'. */
+/* #undef HAVE__BOOL */
+
 /* Define to 1 if your compiler understands __builtin_bswap16. */
 /* #undef HAVE__BUILTIN_BSWAP16 */
 
@@ -606,6 +612,9 @@
 /* A string containing the version number, platform, and C compiler */
 #define PG_VERSION_STR "Uninitialized version string (win32)"
 
+/* The size of `bool', as computed by sizeof. */
+#define SIZEOF_BOOL 0
+
 /* The size of `long', as computed by sizeof. */
 #define SIZEOF_LONG 4