psycopg2: cross compilation fails

[tusj]

Cross compiling psycopg2 currently fails. Psycopg2 is a postgresql adapter for python, and therefore requires postgresql.

The runtime libraries for postgresql needs to be available for the host platform, and the binary pg_config from postgresql needs to be available for the build platform.
Currently, postgresql is only specified in nativeBuildInputs. That makes the pg_config binary available. However, it also makes the runtime libraries available built for build platform, not host platform. From what I understand, to make the runtime libraries for postgresql available for the target platform, postgresql should be added to buildInputs. However, the linking step fails because it still finds the native / build platform libraries.

I'd like to fix this issue myself, but I need some pointers on the best way to proceed. I can see two ways to fix this:

1. The runtime libraries for native should not be available to the linker when building for the host platform.
2. In nativeBuildInputs, specify a postgresql package which does not include the runtime libraries.

Error when building: pkgsCross.armv7l-hf-multiplatform.python39Packages.psycopg2
/nix/store/521z5w03bmrs4d2qxpnbcqk80lvn7p4v-postgresql-13.6-lib/lib/libpq.so: file not recognized: file format not recognized
Examining the file format reveals that it is build for x86-64, the build platform.

[Artturin]

Looks like the bug caused by #177538 and fixed today in #177888

[Artturin]

Oops linked the wrong pr

#169475 caused it