Haskell and postgresql - build error "The program pg_config is required but it could not be found." - postgresql

Question

I am currently learning haskell and just tried using postgresql as a database.
I generated my project with stack (stack new <name> -> stack setup -> stack build)
and then all I changed was adding the dependencies needed to persistent and postgresql to the
package.yaml file (under "dependencies:").
These are:
persistent
persistent-postgresql
persistent-template
This however results in a failing build with the following message:
postgresql-libpq > setup.exe: The program 'pg_config' is required but it could not be found.
postgresql-libpq >
-- While building package postgresql-libpq-0.9.4.2 using:
C:\Users\\AppData\Local\Temp\stack14388\postgresql-libpq-0.9.4.2.stack-work\dist\e626a42b\setup\setup --builddir=.stack-work\dist\e626a42b configure --user --package-db=clear --package-db=global --package-db=C:\sr\snapshots\365a3dde\pkgdb --libdir=C:\sr\snapshots\365a3dde\lib --bindir=C:\sr\snapshots\365a3dde\bin --datadir=C:\sr\snapshots\365a3dde\share --libexecdir=C:\sr\snapshots\365a3dde\libexec --sysconfdir=C:\sr\snapshots\365a3dde\etc --docdir=C:\sr\snapshots\365a3dde\doc\postgresql-libpq-0.9.4.2 --htmldir=C:\sr\snapshots\365a3dde\doc\postgresql-libpq-0.9.4.2 --haddockdir=C:\sr\snapshots\365a3dde\doc\postgresql-libpq-0.9.4.2 --dependency=Cabal=Cabal-2.4.1.0-5rQrtDcYhR2LOcYye7obEr --dependency=Win32=Win32-2.6.1.0 --dependency=base=base-4.12.0.0 --dependency=bytestring=bytestring-0.10.8.2 -f-use-pkg-config --extra-include-dirs=C:\Users\\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\include --extra-lib-dirs=C:\Users\\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\lib --extra-lib-dirs=C:\Users\\AppData\Local\Programs\stack\x86_64-windows\msys2-20180531\mingw64\bin --exact-configuration --ghc-option=-fhide-source-paths
Process exited with code: ExitFailure 1
Does anyone know how to resolve this issue and why it even occurs?
Do I have to install postgresql just for being able to run build the project? If so, how would you
do this in production, when the database could basically lie everywhere?

Answer 1

It looks like Haskell is trying to build with the PostgreSQL client shared library libpq.dll and uses pg_config at build time to determine where PostgreSQL is installed and how it was built.
That would mean that you have to install PostgreSQL on the machine where you build Haskell, including the header files, build environment or however it is called by the installer.
For running Haskell you would only need libpq.dll and the dependent shared libraries.

Answer 2

I solved the issue in Ubuntu with the following command:
apt install libpq-dev