meson: fix csound detection

csound-sys can detect the system lib using either pkg-config or using
the CSOUND_LIB_DIR env variable.
The former case just work but the second is trickier as we need to
ensure that CSOUND_LIB_DIR is defined when building.

So we no longer try to detect the lib using find_library() if user
didn't define the env variable as the build will fail later.

Also explicitly pass the env variable to cargo so user can now call
'CSOUND_LIB_DIR=/usr/lib64 meson build && ninja -C build'
and have it work without repassing the env variable to ninja.

.gitlab-ci.yml

@@ -153,17 +153,22 @@ test nightly:
   rules:
     - if: '$UPDATE_IMG == null || $UPDATE_IMG == "nightly"'
 
-meson shared:
+.meson:
   extends: .img-stable
+  rules:
+    - if: '$UPDATE_IMG == null || $UPDATE_IMG == "stable"'
+  variables:
+    CSOUND_LIB_DIR: '/usr/lib'
+
+meson shared:
+  extends: .meson
   script:
     - meson build --default-library=shared --prefix=$(pwd)/install
     - ninja -C build install
     - ./ci/check-plugins-installed.py install
-  rules:
-    - if: '$UPDATE_IMG == null || $UPDATE_IMG == "stable"'
 
 meson static:
-  extends: .img-stable
+  extends: .meson
   script:
     - meson build --default-library=static --prefix=$(pwd)/install -Dsodium=built-in
     - ninja -C build install
@@ -172,8 +177,6 @@ meson static:
     - PKG_CONFIG_PATH=$PKG_CONFIG_PATH:$(pwd)/../install/lib/x86_64-linux-gnu/pkgconfig meson build
     - ninja -C build
     - ./build/test-gst-static
-  rules:
-    - if: '$UPDATE_IMG == null || $UPDATE_IMG == "stable"'
 
 rustfmt:
   extends: .img-stable

meson.build

@@ -78,23 +78,27 @@ endif
 
 cc = meson.get_compiler('c')
 csound_option = get_option('csound')
-csound_dep = dependency('', required: false) # not-found dependency
-if not csound_option.disabled()
-  csound_dep = cc.find_library('csound64', required: false)
-  if not csound_dep.found()
-    python3 = import('python').find_installation('python3')
-    res = run_command(python3, '-c', 'import os; print(os.environ["CSOUND_LIB_DIR"])')
-    if res.returncode() == 0
-      csound_dep = cc.find_library('csound64', dirs: res.stdout(), required: csound_option)
-    elif csound_option.enabled()
-      error('csound option is enabled, but csound64 library could not be found and CSOUND_LIB_DIR was not set')
+# try first to find csound using pkg-config
+csound_dep = dependency('', required: false)
+if not csound_dep.found() and not csound_option.disabled()
+  # if csound isn't distributed with pkg-config then user needs to define CSOUND_LIB_DIR with its location
+  python3 = import('python').find_installation('python3')
+  res = run_command(python3, '-c', 'import os; print(os.environ["CSOUND_LIB_DIR"])')
+  if res.returncode() == 0
+    csound_libdir = res.stdout().strip()
+    csound_dep = cc.find_library('csound64', dirs: csound_libdir, required: false)
+    if csound_dep.found()
+      extra_env += {'CSOUND_LIB_DIR': csound_libdir}
     endif
   endif
 endif
 
 if csound_dep.found()
   plugins_rep += {'audio/csound' : 'libgstcsound'}
+elif csound_option.enabled()
+  error('csound option is enabled, but csound64 library could not be found and CSOUND_LIB_DIR was not set')
 else
+  message('csound not found, disabling its plugin')
   exclude += ['audio/csound']
 endif