Add a new subproject 'win-flex-bison-binaries'

This subproject will download and provide win32 binaries for flex
and/or bison if they aren't found at configure time on Windows.

meson.build

@@ -14,6 +14,7 @@ subprojects = [
     'gst-plugins-good',
 ]
 
+build_system = build_machine.system()
 cc = meson.get_compiler('c')
 
 # Make it possible to use msys2 built zlib which fails
@@ -130,6 +131,13 @@ foreach custom_subproj: get_option('custom_subprojects').split(',')
     endif
 endforeach
 
+# On Windows, if flex/bison aren't found, we use a subproject to get them
+flex = find_program('flex', 'win_flex', required : build_system != 'windows')
+bison = find_program('bison', 'win_bison', required : build_system != 'windows')
+if not flex.found() or not bison.found()
+  subproject('win-flex-bison-binaries')
+endif
+
 message('Building subprojects: ' + ', '.join(subprojects))
 foreach subproj: subprojects
     subproject(subproj, version: gst_version)

subprojects/win-flex-bison-binaries/.gitignore

@@ -0,0 +1,9 @@
+*.sw[op]
+*~
+custom_build_rules
+data/
+FlexLexer.h
+README.txt
+UNISTD_ERROR.readme
+*.exe
+*.zip

subprojects/win-flex-bison-binaries/download-binary.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+import ssl
+import zipfile
+import hashlib
+import urllib.request
+
+# Disable certificate checking because it always fails on Windows
+# We verify the checksum anyway.
+ctx = ssl.create_default_context()
+ctx.check_hostname = False
+ctx.verify_mode = ssl.CERT_NONE
+
+base_url = 'https://sourceforge.net/projects/winflexbison/files/win_flex_bison-{}.zip'
+url = base_url.format(sys.argv[1])
+zip_sha256 = sys.argv[2]
+source_dir = os.path.join(os.environ['MESON_SOURCE_ROOT'], os.environ['MESON_SUBDIR'])
+dest = os.path.basename(url)
+dest_path = os.path.join(source_dir, dest)
+
+def get_sha256(zipf):
+    hasher = hashlib.sha256()
+    with open(zipf, 'rb') as f:
+        hasher.update(f.read())
+    return hasher.hexdigest()
+
+if os.path.isfile(dest_path):
+    found_sha256 = get_sha256(dest_path)
+    if found_sha256 == zip_sha256:
+        print('{} already downloaded'.format(dest))
+        sys.exit(0)
+    else:
+        print('{} checksum mismatch, redownloading'.format(dest))
+
+print('Downloading {} to {}'.format(url, dest))
+with open(dest_path, 'wb') as d:
+    f = urllib.request.urlopen(url, context=ctx)
+    d.write(f.read())
+
+found_sha256 = get_sha256(dest_path)
+if found_sha256 != zip_sha256:
+    print('SHA256 of downloaded file {} was {} instead of {}'
+          ''.format(dest, found_sha256, zip_sha256))
+    sys.exit(1)
+
+print('Extracting {}'.format(dest))
+zf = zipfile.ZipFile(dest_path, "r")
+zf.extractall(path=source_dir)

subprojects/win-flex-bison-binaries/meson.build

@@ -0,0 +1,25 @@
+project('win-flex-bison-binary', version : '2.5.14')
+
+provide_flex = not find_program('flex', required : false).found()
+provide_bison = not find_program('bison', required : false).found()
+
+if provide_flex or provide_bison
+  py3 = import('python3').find_python()
+
+  message('Downloading and extracting win-flex-bison binaries...')
+
+  zip_hash = '354c9aae02aca421c52abfda7fe3ce6c32ad07e25ff3f66e31da9437a0b906cf'
+
+  ret = run_command(py3, files('download-binary.py'), meson.project_version(), zip_hash)
+  if ret.returncode() != 0
+    message(ret.stdout())
+    error(ret.stderr())
+  endif
+
+  if provide_flex
+    meson.override_find_program('flex', find_program('win_flex'))
+  endif
+  if provide_bison
+    meson.override_find_program('bison', find_program('win_bison'))
+  endif
+endif