add meson support

This is needed to integrate gst-plugins-rs with gst-build, see
https://gitlab.freedesktop.org/gstreamer/gst-build/issues/63

cargo.py

@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+
+import glob
+import os
+import os.path
+import shutil
+import subprocess
+import sys
+
+meson_build_dir, meson_current_source_dir, meson_build_root, target, ext = sys.argv[1:]
+
+cargo_target_dir = os.path.join(meson_build_dir, 'target')
+
+env = os.environ.copy()
+env['CARGO_TARGET_DIR'] = cargo_target_dir
+
+# FIXME: hack so cargo will find gst libs when building inside gst-build.
+# We should fetch this from meson deps instead of hardcoding the paths,
+# when Meson will generate -uninstalled.pc files, they all will be in
+# <meson_build_root>/meson-uninstalled/
+pkg_config_path = env.get('PKG_CONFIG_PATH', '').split(':')
+pkg_config_path.append(os.path.join(
+    meson_build_root, 'subprojects', 'gstreamer', 'pkgconfig'))
+pkg_config_path.append(os.path.join(
+    meson_build_root, 'subprojects', 'gst-plugins-base', 'pkgconfig'))
+env['PKG_CONFIG_PATH'] = ':'.join(pkg_config_path)
+
+# cargo build
+cargo_cmd = ['cargo', 'build', '--manifest-path',
+             os.path.join(meson_current_source_dir, 'Cargo.toml')]
+if target == 'release':
+    cargo_cmd.append('--release')
+
+try:
+    subprocess.run(cargo_cmd, env=env, check=True)
+except subprocess.SubprocessError:
+    sys.exit(1)
+
+# Copy so files to build dir
+for f in glob.glob(os.path.join(cargo_target_dir, target, '*.' + ext)):
+    shutil.copy(f, meson_build_dir)

meson.build

@@ -0,0 +1,64 @@
+project('gst-plugins-rs',
+        'rust',
+        version: '0.13.0',
+        meson_version : '>= 0.52')
+
+if get_option('debug')
+  target = 'debug'
+else
+  target = 'release'
+endif
+
+cargo = find_program('cargo', version:'>=1.39')
+cargo_script = find_program('cargo.py')
+
+system = build_machine.system()
+if system == 'windows'
+  ext = 'dll'
+elif system == 'darwin'
+  ext = 'dylib'
+else
+  ext = 'so'
+endif
+
+plugins_rep = {
+  'gst-plugin-audiofx': 'libgstrsaudiofx',
+  'gst-plugin-cdg': 'libgstcdg',
+  'gst-plugin-closedcaption': 'libgstrsclosedcaption',
+  'gst-plugin-fallbackswitch': 'libgstfallbackswitch',
+  'gst-plugin-file': 'libgstrsfile',
+  'gst-plugin-flv': 'libgstrsflv',
+  'gst-plugin-lewton': 'libgstlewton',
+  'gst-plugin-rav1e': 'libgstrav1e',
+  'gst-plugin-reqwest': 'libgstreqwest',
+  'gst-plugin-rusoto': 'libgstrusoto',
+  'gst-plugin-sodium': 'libgstsodium',
+  'gst-plugin-threadshare': 'libgstthreadshare',
+  'gst-plugin-togglerecord': 'libgsttogglerecord',
+}
+
+output = []
+
+foreach p, lib : plugins_rep
+  # Add the plugin file as output
+  output += [lib + '.' + ext]
+endforeach
+
+# Always build the target so we don't have to list all source files as input
+rs_plugins = custom_target('gst-plugins-rs',
+  build_by_default: true,
+  output: output,
+  console: true,
+  install: false,
+  build_always_stale: true,
+  command: [cargo_script,
+    meson.current_build_dir(),
+    meson.current_source_dir(),
+    meson.build_root(),
+    target,
+    ext])
+
+# FIXME: raises a warning as the target has multiple outputs and meson will use
+# only the first one. All the plugins have the same basedir, hence
+# GST_PLUGIN_PATH will include them all, so that's ok.
+plugins = [rs_plugins]