Bug 1522135 - Make .ycm_extra_conf.py work with python3. r=jgraham

By calling into mach instead, which knows how to get to run itself with the
right python version.

Differential Revision: https://phabricator.services.mozilla.com/D17371

.ycm_extra_conf.py

@@ -2,25 +2,23 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-import imp
+from __future__ import absolute_import, print_function
+import json
 import os
 import shlex
+import subprocess
 import sys
-try:
-    from StringIO import StringIO
-except ImportError:
-    from io import StringIO
 
 old_bytecode = sys.dont_write_bytecode
 sys.dont_write_bytecode = True
 
-path = os.path.join(os.path.dirname(__file__), 'mach')
+path = os.path.abspath(os.path.join(os.path.dirname(__file__), 'mach'))
 
+# If mach is not here, we're on the objdir go to the srcdir.
 if not os.path.exists(path):
-    path = os.path.join(os.path.dirname(__file__), 'config.status')
-    config = imp.load_module('_buildconfig', open(path), path, ('', 'r', imp.PY_SOURCE))
-    path = os.path.join(config.topsrcdir, 'mach')
-mach_module = imp.load_module('_mach', open(path), path, ('', 'r', imp.PY_SOURCE))
+    with open(os.path.join(os.path.dirname(__file__), 'mozinfo.json')) as info:
+        config = json.loads(info.read())
+    path = os.path.join(config['topsrcdir'], 'mach')
 
 sys.dont_write_bytecode = old_bytecode
 
@@ -35,16 +33,10 @@ def _is_likely_cpp_header(filename):
     return os.path.exists(cpp_file)
 
 def FlagsForFile(filename):
-    mach = mach_module.get_mach()
-    out = StringIO()
+    output = subprocess.check_output([path, 'compileflags', filename])
+    output = output.decode('utf-8')
 
-    # Mach calls sys.stdout.fileno(), so we need to fake it when capturing it.
-    # Returning an invalid file descriptor does the trick.
-    out.fileno = lambda: -1
-    out.encoding = None
-    mach.run(['compileflags', filename], stdout=out, stderr=out)
-
-    flag_list = shlex.split(out.getvalue())
+    flag_list = shlex.split(output)
 
     # This flag is added by Fennec for android build and causes ycmd to fail to parse the file.
     # Removing this flag is a workaround until ycmd starts to handle this flag properly.
@@ -58,3 +50,6 @@ def FlagsForFile(filename):
         'flags': final_flags,
         'do_cache': True
     }
+
+if __name__ == '__main__':
+    print(FlagsForFile(sys.argv[1]))