fix grass plugin build (followup d2078b00)

[jef-n]

No description provided.

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit 453ea56)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit 453ea56)

[m-kuhn]

@jef-n do you still have the build error around somewhere?

[jef-n]

@jef-n do you still have the build error around somewhere?

In file included from /usr/lib/grass84/include/grass/vect/digit.h:3,
                 from /usr/lib/grass84/include/grass/vector.h:4,
                 from /build/qgis-3.41.0+git20241231+834b94b0c01+99sid/src/providers/grass/qgsgrassvectormaplayer.h:38,
                 from /build/qgis-3.41.0+git20241231+834b94b0c01+99sid/src/providers/grass/qgsgrassvectormap.h:26,
                 from /build/qgis-3.41.0+git20241231+834b94b0c01+99sid/src/plugins/grass/qgsgrasseditrenderer.cpp:29:
/usr/lib/grass84/include/grass/vect/dig_structs.h:31:10: fatal error: libpq-fe.h: No such file or directory
   31 | #include <libpq-fe.h>
      |          ^~~~~~~~~~~~
compilation terminated.

[m-kuhn]

This should be added to a grass target and because we don't have that to the grass provider instead.
Does it help if you add PostgreSQL::PostgreSQL here https://github.com/qgis/QGIS/blob/master/src/providers/grass/CMakeLists.txt#L135 ?

[dhdeangelis]

It seems that now building QGIS with GRASS 8 but without PostgreSQL is not possible, as it complains that lib PostgreSQL::PostgreSQL is not found.

[m-kuhn]

Interesting scenario.
@dhdeangelis can you try to change src/providers/grass/CMakeLists.txt:135 to

target_link_libraries(qgisgrass${GRASS_BUILD_VERSION} ${GRASS_TARGET_LINK_LIBRARIES${GRASS_BUILD_VERSION}})
if(WITH_POSTGRESQL)
  target_link_libraries(qgisgrass${GRASS_BUILD_VERSION} PostgreSQL::PostgreSQL)
endif()

This should recover the status quo. It's not ideal as it requires QGIS to be built with PostgreSQL support if grass is built with PostgreSQL support, but I guess that's acceptable.
If it works, it would be great if you could open a pull request.

[dhdeangelis]

@m-kuhn thank you for your recommendation, I have now implemented, tested locally OK and submitted a PR on this

#60260