meson: Modernize opencv build definitions

Use the fs module instead of using `run_command('test')`, simplify
some indentation, fix dependency management

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8418>

subprojects/gst-plugins-bad/ext/opencv/meson.build

@@ -66,12 +66,10 @@ plugin_sources += {
   'opencv': pathsep.join(doc_sources)
 }
 
-if get_option('opencv').disabled()
+if get_option('opencv').disabled() or not opencv_dep.found()
-  opencv_dep = disabler()
   subdir_done()
 endif
 
-if opencv_found
 gstopencv = library('gstopencv',
   gstopencv_sources,
   cpp_args : gst_plugins_bad_args + gstopencv_cargs + [ '-DGST_USE_UNSTABLE_API' ],
@@ -82,6 +80,3 @@ if opencv_found
   install_dir : plugins_install_dir,
 )
 plugins += [gstopencv]
-elif get_option('opencv').enabled()
-  error('OpenCV support enabled but required dependencies were not found.')
-endif

subprojects/gst-plugins-bad/gst-libs/gst/opencv/meson.build

@@ -1,5 +1,6 @@
-if get_option('opencv').disabled()
+opencv_opt = get_option('opencv')
-  gstopencv_dep = disabler()
+if opencv_opt.disabled()
+  opencv_dep = disabler()
   subdir_done()
 endif
 
@@ -27,24 +28,29 @@ libopencv_headers = [
 
 
 gstopencv_cargs = ['-DGST_HAAR_CASCADES_DIR="@0@"']
-
 opencv_dep = dependency('opencv', version : ['>= 3.0.0', '< 3.5.0'], required : false)
-opencv_found = opencv_dep.found()
+if not opencv_dep.found()
-if not opencv_found
+  opencv_dep = dependency('opencv', version : ['>= 4.0.0'], required : opencv_opt)
-  opencv_dep = dependency('opencv4', version : ['>= 4.0.0'], required : false)
+  if not opencv_dep.found()
-  opencv_found = opencv_dep.found()
+    subdir_done()
+  endif
 endif
 
-if opencv_found
+opencv_found = true
 foreach h : libopencv_headers
   if not cxx.has_header(h, dependencies: opencv_dep)
     message('Needed header "' + h + '" not found')
     opencv_found = false
   endif
 endforeach
+
+if not opencv_found
+  if opencv_opt.enabled()
+    error('opencv enabled, but needed headers not found')
+  endif
+  subdir_done()
 endif
 
-if opencv_found
 opencv_prefix = opencv_dep.get_variable('prefix')
 gstopencv_cargs += ['-DOPENCV_PREFIX="' + opencv_prefix + '"']
 # opencv4 seems to ship with .pc file that references non-existent include dir
@@ -55,26 +61,24 @@ if opencv_found
 
 # Check the data dir used by opencv for its xml data files
 # Use prefix from pkg-config to be compatible with cross-compilation
-  r = run_command('test', '-d', opencv_prefix + '/share/opencv', check: false)
+fsmod = import('fs')
-  if r.returncode() == 0
+opencv_path_name = ''
-    gstopencv_cargs += '-DOPENCV_PATH_NAME="opencv"'
+foreach d : ['opencv', 'OpenCV', 'opencv4']
-  else
+  if fsmod.is_dir(opencv_prefix / 'share' / d)
-    r = run_command('test', '-d', opencv_prefix + '/share/OpenCV', check: false)
+    opencv_path_name = d
-    if r.returncode() == 0
+    break
-      gstopencv_cargs += '-DOPENCV_PATH_NAME="OpenCV"'
+  endif
-    else
+endforeach
-      r = run_command('test', '-d', opencv_prefix + '/share/opencv4', check: false)
+if opencv_path_name != ''
-      if r.returncode() == 0
+  gstopencv_cargs += [f'-DOPENCV_PATH_NAME="@d@"']
-        gstopencv_cargs += '-DOPENCV_PATH_NAME="opencv4"'
 else
+  if opencv_opt.enabled()
+    error('opencv enabled, but data directory not found')
+  endif
   message('Unable to detect OpenCV data directory')
-        opencv_found = false
+  subdir_done()
-      endif
-    endif
-  endif
 endif
 
-if opencv_found
 pkg_name = 'gstreamer-opencv-1.0'
 gstopencv = library('gstopencv-' + api_version,
   opencv_sources,
@@ -105,8 +109,3 @@ if opencv_found
 meson.override_dependency(pkg_name, gstopencv_dep)
 
 install_headers(opencv_headers, subdir : 'gstreamer-1.0/gst/opencv')
-elif get_option('opencv').enabled()
-  error('OpenCV support enabled but required dependencies were not found.')
-else
-  gstopencv_dep = disabler()
-endif