Library Linking is not Working

[azertyIA]

I wanted to try what backend development would be like in Haskell, so I'm kind of new to this, but I keep getting this error log. I tried setting my env path to the Postgres 17 libs and bins, and a bunch of other alternatives, and it seems it found some form of a libpq file. Still, there's not enough information or context on what library linking even means here, so I'm probably missing something big (for example using Windows might just be a massive hindrance).

checking for the pg_config program... C:\Program Files\PostgreSQL\17\bin\pg_config.exe
checking for the PostgreSQL libraries CPPFLAGS... -IC:/PROGRA~1/POSTGR~1/17/include
checking for the PostgreSQL libraries LDFLAGS... -LC:/PROGRA~1/POSTGR~1/17/lib
checking for the PostgreSQL libraries LIBS... -lpq 
checking for the PostgreSQL version... 17.2        
checking if PostgreSQL version 17.2 is >= 10.22... yes
checking for libpq-fe.h... yes
checking for the PostgreSQL library linking is working... no

[phadej]

what library linking even means here,

configure script tries to compile a simple C program, which should link against postgresql client library. There is a chance that the script is misguided, but more likely that's an issue with your setup

You can try to debug it yourself:

cabal get postgresql-libpq-configure
cd postgresql-libpq-configure-0.11
sh configure

or even just by trying to compile

#include <libpq-fe.h>

int
main (void)
{

		    char conninfo[]="dbname = postgres";
		    PGconn     *conn;
		    conn = PQconnectdb(conninfo);

  return 0;
}

program first

[azertyIA]

It looks like I'm just having an error compiling the script you gave. I almost have everything working, but I can't do anything if I don't link the library argument like so:

gcc sample.c -m64 -L "C:/Program FIles/Postgresql/17/bin" -lpq  

I tried including "C:/Program FIles/Postgresql/17/bin" in both LIBRARY_PATH and LD_LIBRARY_PATH envs, but I haven't gotten anywhere far yet. If I don't link the library argument then I get errors like (there's a hundred more using -lpq):

C:/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/13.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:/Program Files/PostgreSQL/17/bin/../lib/libpq.a(src/interfaces/libpq/libpq.a.p/fe-secure-openssl.c.obj):(.text$mn+0x4d): undefined reference to `pg_snprintf'

Edit: I have tried changing -lpq to -llibpq because I figured out what -l actually does and this compiles fine, so if I want cabal build to finally work, I just need to somehow auto-include that -l argument:

gcc sample.c -m64 -l libpq

Edit 2: I was messing around some more and I tried changing the configure script to use -llibpq instead of -lpq and it actually linked all the way through. I'm not sure why it should work though. Maybe on later versions it just got renamed, so for now I'll just make a copy of the library and rename it "pq," which didn't end up working.

[azertyIA]

By the looks of it, -lpq typically works because apt get libpq-dev (or something along those lines) just has pq as its library file, I'm guessing. But there is no equivalent to Windows, except for the entire Postgres installation which uses libpq and needs the -llibpq argument.

[phadej]

Ok. So something has changed since Postgres14 in Windows installation as I'm able to reproduce in #78

[phadej]

I cannot find any reasons why linking suddelnly fails with PostgreSQL 17.

https://stackoverflow.com/questions/79205379/how-to-link-to-libpq-postgresql-c-library-for-postgresql-v17-1 workaround seems to be to downgrade to 16, and I cannot find any other reports.

[phadej]

After a bit of testing in CI, it seems that linking issue is not related to postgresql-libpq at all. I'm not able to successfully link anything against postgresql17 package from chocolatey repository.

I'll keep this issue open though, as its still unclear what the exact issue is. It seems its a mistake in chocolatey packaging, but we'll hopefully get more info soon.

[pecsaeta]

I've encountered the same issue on Windows with PostgreSQL 18, and 17 didn't work either.
As suggested above, downgrading to 16 'solved' it for me!