Re: BUG #15349: "make installcheck -C src/interfaces/libpq" fails

Hello,
> The following bug has been logged on the website:
>
> Bug reference: 15349
> Logged by: Alexander Lakhin
> Email address: exclusion(at)gmail(dot)com
> PostgreSQL version: 11beta3
> Operating system: Ubuntu 18.04
> Description:
>
> With REL_11_STABLE (also reproduced with versions 10 and 9.6) "make
> installcheck -C src/interfaces/libpq" fails:
> ./configure && make
> make installcheck -C src/interfaces/libpq # or make all -C src/interfaces/libpq/test/
>
> gcc -L../../../../src/port -L../../../../src/common -L../../../../src/common -lpgcommon -L../../../../src/port -lpgport -L../../../../src/interfaces/libpq -lpq -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags uri-regress.o -o uri-regress
> uri-regress.o: In function `main':
> uri-regress.c:(.text.startup+0x60): undefined reference to `PQconninfoParse'
> uri-regress.c:(.text.startup+0x71): undefined reference to `PQconndefaults'
> collect2: error: ld returned 1 exit status
> <builtin>: recipe for target 'uri-regress' failed
> make: *** [uri-regress] Error 1
>
> If I restore previous version of libpq/test/Makefile:
> git show dddfc4cb~1:src/interfaces/libpq/test/Makefile
>> src/interfaces/libpq/test/Makefile
> then "make all -C src/interfaces/libpq/test/" succeeds:
> gcc -L../../../../src/port -L../../../../src/common -Wl,--as-needed -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags uri-regress.o -L../../../../src/common -lpgcommon -L../../../../src/port -lpgport -L../../../../src/interfaces/libpq -lpq -o uri-regress
> make: Leaving directory '/space/tmp/postgres.chk/src/interfaces/libpq/test'
As I found out, this issue is caused by --as-needed flag and wrong
linking order.
The following command (generated with the new Makefile) fails:
gcc -L../../../../src/port -L../../../../src/common
-L../../../../src/common -lpgcommon -L../../../../src/port -lpgport
-L../../../../src/interfaces/libpq -lpq -Wl,--as-needed
-Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags  uri-regress.o -o
uri-regress

But when I place '-lpq' after 'uri-regress.o', the compilation succeeds:
gcc -L../../../../src/port -L../../../../src/common
-L../../../../src/common -lpgcommon -L../../../../src/port -lpgport
-L../../../../src/interfaces/libpq -Wl,--as-needed
-Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags uri-regress.o -lpq
-o uri-regress

This behavior is documented in
https://wiki.gentoo.org/wiki/Project:Quality_Assurance/As-needed#Importance_of_linking_order

BTW, I wonder why it's not reproduced on Fedora (27, 28) and whether
this check is performed in BuildFarm.

Best regards,
------
Alexander Lakhin
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company