Add support for Meson build system

Tested on:
 - Linux/x86* with gcc
 - Android armv7 arm64 x86 x86_64 with clang
 - Windows x86 x86_64 with Visual Studio 2017
 - Windows x86 x86_64 with MinGW
 - macOS x86_64 with clang
 - iOS arm64 x86_64 with clang

Co-authored by: Nirbheek Chauhan <nirbheek@centricular.com>

https://gitlab.xiph.org/xiph/opus/-/merge_requests/13

meson/get-version.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python3
+#
+# Opus get-version.py
+#
+# Extracts versions for build:
+#  - Opus package version based on 'git describe' or $srcroot/package_version
+#  - libtool version based on configure.ac
+#  - macos lib version based on configure.ac
+#
+# Usage:
+# get-version.py [--package-version | --libtool-version | --darwin-version]
+import argparse
+import subprocess
+import os
+import sys
+import shutil
+
+if __name__ == '__main__':
+    arg_parser = argparse.ArgumentParser(description='Extract Opus package version or libtool version')
+    group = arg_parser.add_mutually_exclusive_group(required=True)
+    group.add_argument('--libtool-version', action='store_true')
+    group.add_argument('--package-version', action='store_true')
+    group.add_argument('--darwin-version', action='store_true')
+    args = arg_parser.parse_args()
+
+    srcroot = os.path.normpath(os.path.join(os.path.dirname(__file__), '..'))
+
+    # package version
+    if args.package_version:
+        package_version = None
+
+        # check if git checkout
+        git_dir = os.path.join(srcroot, '.git')
+        is_git = os.path.isdir(git_dir)
+        have_git = shutil.which('git') is not None
+
+        if is_git and have_git:
+            git_cmd = subprocess.run(['git', '--git-dir=' + git_dir, 'describe', 'HEAD'], stdout=subprocess.PIPE)
+            if git_cmd.returncode:
+                print('ERROR: Could not extract package version via `git describe` in', srcroot, file=sys.stderr)
+                sys.exit(-1)
+            package_version = git_cmd.stdout.decode('ascii').strip().lstrip('v')
+        else:
+            with open(os.path.join(srcroot, 'package_version'), 'r') as f:
+                for line in f:
+                    if line.startswith('PACKAGE_VERSION="'):
+                        package_version = line[17:].strip().lstrip('v').rstrip('"')
+                    if package_version:
+                        break
+
+        if not package_version:
+            print('ERROR: Could not extract package version from package_version file in', srcroot, file=sys.stderr)
+            sys.exit(-1)
+
+        print(package_version)
+        sys.exit(0)
+
+    # libtool version + darwin version
+    elif args.libtool_version or args.darwin_version:
+        opus_lt_cur = None
+        opus_lt_rev = None
+        opus_lt_age = None
+
+        with open(os.path.join(srcroot, 'configure.ac'), 'r') as f:
+            for line in f:
+                if line.strip().startswith('OPUS_LT_CURRENT='):
+                    opus_lt_cur = line[16:].strip()
+                elif line.strip().startswith('OPUS_LT_REVISION='):
+                    opus_lt_rev = line[17:].strip()
+                elif line.strip().startswith('OPUS_LT_AGE='):
+                    opus_lt_age = line[12:].strip()
+
+        if opus_lt_cur and opus_lt_rev and opus_lt_age:
+            opus_lt_cur = int(opus_lt_cur)
+            opus_lt_rev = int(opus_lt_rev)
+            opus_lt_age = int(opus_lt_age)
+            if args.libtool_version:
+              print('{}.{}.{}'.format(opus_lt_cur - opus_lt_age, opus_lt_age, opus_lt_rev))
+            elif args.darwin_version:
+              print('{}.{}.{}'.format(opus_lt_cur + 1, 0, 0))
+            sys.exit(0)
+        else:
+            print('ERROR: Could not extract libtool version from configure.ac file in', srcroot, file=sys.stderr)
+            sys.exit(-1)
+    else:
+        sys.exit(-1)