From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Should contrib modules install .h files?
In-Reply-To: <86036c67-d76f-3dc0-a9f5-69e776b4ecc5@2ndquadrant.com> (Peter
	Eisentraut's message of "Wed, 1 Aug 2018 00:40:25 +0200")
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Date: Wed, 01 Aug 2018 00:33:11 +0100
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>>>>> "Peter" == Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:

 >> A review of contrib/ suggested that cube, hstore, isn, ltree and seg
 >> were the only modules that had useful headers to install, so do
 >> those.

 Peter> I'm missing some guidance what an extension using those headers
 Peter> is supposed to do. How does it get the right -I options?

All of the below assumes PGXS.

If your extension is relying on pg11+, or you have checked the pg
version when constructing the makefile, you can just do:

PG_CPPFLAGS += -I$(includedir_server)/extension/hstore

and #include "hstore.h" will work.

If you need to workaround for old versions in one makefile, as I do,
then you can do something along these lines (this goes before the
include $(PGXS) line):

# MAJORVERSION and includedir_server are not defined yet, but will be
# defined before PG_CPPFLAGS is expanded. So we use conditional
# expansions rather than 'ifeq' syntax.

# for pg11+, hstore.h will be installed here
HSTORE_INCDIR = $(includedir_server)/extension/hstore

# for pg 9.5/9.6/10, we have a local copy of hstore.h since it happens
# to be the same, barring non-semantic whitespace, between the three
# versions
HSTORE_INCDIR_OLD = old_inc

PG_CPPFLAGS += -I$(HSTORE_INCDIR$(if $(filter 9.% 10,$(MAJORVERSION)),_OLD))

If you need to distinguish more versions for whatever reason you can do
this:

HSTORE_INCDIR = $(includedir_server)/extension/hstore
HSTORE_INCDIR_10 =  whatever
HSTORE_INCDIR_9.6 = whatever
HSTORE_INCDIR_9.5 = whatever
HSTORE_INCDIR_9.4 = whatever
HSTORE_INCDIR_9.3 = whatever
PG_CPPFLAGS += -I$(HSTORE_INCDIR$(if $(filter 9.% 10,$(MAJORVERSION)),_$(MAJORVERSION)))

-- 
Andrew (irc:RhodiumToad)