From: Tom Lane <tgl@sss.pgh.pa.us>
To: Amit Kapila <amit.kapila16@gmail.com>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
        Andrew Gierth <andrew@tao11.riddles.org.uk>,
        Michael Meskes <meskes@postgresql.org>
Subject: Re: define bool in pgtypeslib_extern.h
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Comments: In-reply-to Amit Kapila <amit.kapila16@gmail.com>
	message dated "Sat, 26 Oct 2019 08:51:14 +0530"
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Date: Sat, 26 Oct 2019 13:19:24 -0400
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Amit Kapila <amit.kapila16@gmail.com> writes:
> On Fri, Oct 25, 2019 at 9:55 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> However, we're not out of the woods, because lookee here in
>> ecpglib.h:
>> #ifndef bool
>> #define bool char
>> #endif                          /* ndef bool */
>> I'm more than slightly surprised that we haven't already seen
>> problems due to this conflicting with d26a810eb.

> I think it is because it never gets any imports from c.h.

On closer inspection, it seems to be just blind luck.  For example,
if I rearrange the inclusion order in a file using ecpglib.h:

diff --git a/src/interfaces/ecpg/ecpglib/data.c b/src/interfaces/ecpg/ecpg=
lib/data.c
index 7d2a78a..09944ff 100644
--- a/src/interfaces/ecpg/ecpglib/data.c
+++ b/src/interfaces/ecpg/ecpglib/data.c
@@ -6,8 +6,8 @@
 #include <math.h>
 =

 #include "ecpgerrno.h"
-#include "ecpglib.h"
 #include "ecpglib_extern.h"
+#include "ecpglib.h"
 #include "ecpgtype.h"
 #include "pgtypes_date.h"
 #include "pgtypes_interval.h"

then on a PPC Mac I get

data.c:210: error: conflicting types for 'ecpg_get_data'
ecpglib_extern.h:167: error: previous declaration of 'ecpg_get_data' was h=
ere

It's exactly the same problem as we saw with pgtypeslib_extern.h:
header ordering changes affect the meaning of uses of bool, and that's
just not acceptable.

In this case it's even worse because we're mucking with type definitions
in a user-visible header.  I'm surprised we've not gotten bug reports
about that.  Maybe all ECPG users include <stdbool.h> before they
include ecpglib.h, but that doesn't exactly make things worry-free either,
because code doing that will think that these functions return _Bool,
when the compiled library possibly thinks differently.  Probably the
only thing saving us is that sizeof(_Bool) is 1 on just about every
platform in common use nowadays.

I'm inclined to think that we need to make ecpglib.h's bool-related
definitions exactly match c.h, which will mean that it has to pull in
<stdbool.h> on most platforms, which will mean adding a control symbol
for that to ecpg_config.h.  I do not think we should export
HAVE_STDBOOL_H and SIZEOF_BOOL there though; probably better to have
configure make the choice and export something named like PG_USE_STDBOOL.

			regards, tom lane