Add write_config installer directive

docs/installers.rst

@@ -204,6 +204,27 @@ Example:
         args: --argh
         file: great-id
 
+Writing into an INI type config file
+------------------------------------
+
+Modify or create a config file with the ``set_config`` directive. A config file
+is a text file composed of key=value (or key: value) lines grouped under
+[sections]. Use the ``file`` (an absolute path or a ``file id``), ``section``,
+``key`` and ``value`` parameters. Not that the file is entirely rewritten and
+comments are left out; Make sure to compare the initial and resulting file
+to spot any potential parsing issues.
+
+Example:
+
+::
+
+    - set_config:
+        file: $GAMEDIR/game.ini
+        section: Engine
+        key: Renderer
+        value: OpenGL
+
+
 Running a task provided by a runner
 -----------------------------------
 

lutris/installer.py

@@ -14,6 +14,7 @@ from gi.repository import Gtk, Gdk
 
 from lutris import pga
 from lutris.util import extract, devices
+from lutris.util.fileio import EvilConfigParser, MultiOrderedDict
 from lutris.util.jobs import async_call
 from lutris.util.log import logger
 from lutris.util.strings import slugify, add_url_tags
@@ -558,6 +559,33 @@ class ScriptInterpreter(object):
         logger.debug("extracting file %s to %s", filename, dest_path)
         extract.extract_archive(filename, dest_path, merge_single, extractor)
 
+    def write_config(self, params):
+        """Writes a key-value pair into an INI type config file."""
+        # Get file
+        if 'file' not in params:
+            raise ScriptingError('"file" parameter is mandatory for the '
+                                 'write_conf command', params)
+        config_file = self._get_file(params['file'])
+        if not config_file:
+            config_file = self._substitute(params['file'])
+
+        # Create it if necessary
+        basedir = os.path.dirname(config_file)
+        if not os.path.exists(basedir):
+            os.makedirs(basedir)
+
+        parser = EvilConfigParser(allow_no_value=True,
+                                  dict_type=MultiOrderedDict)
+        parser.optionxform = str  # Preserve text case
+        parser.read(config_file)
+
+        if not parser.has_section(params['section']):
+            parser.add_section(params['section'])
+        parser.set(params['section'], params['key'], params['value'])
+
+        with open(config_file, 'wb') as f:
+            parser.write(f)
+
     def _append_steam_data_to_files(self, runner_class):
         steam_runner = runner_class()
         data_path = steam_runner.get_game_path_from_appid(

lutris/util/fileio.py

@@ -0,0 +1,27 @@
+from collections import OrderedDict
+from ConfigParser import RawConfigParser
+
+
+class EvilConfigParser(RawConfigParser):
+    """ConfigParser with support for evil INIs using duplicate keys."""
+    def write(self, fp):
+        for section in self._sections:
+            fp.write("[%s]\n" % section)
+            for (key, value) in self._sections[section].items():
+                if key == "__name__":
+                    continue
+                if (value is not None) or (self._optcre == self.OPTCRE):
+                    # Duplicate keys writing support inside
+                    key = "=".join((key,
+                                    str(value).replace('\n', '\n%s=' % key)))
+                fp.write("%s\n" % (key))
+            fp.write("\n")
+
+
+class MultiOrderedDict(OrderedDict):
+    """dict_type to use with an EvilConfigParser instance."""
+    def __setitem__(self, key, value):
+        if isinstance(value, list) and key in self:
+            self[key].extend(value)
+        else:
+            super(MultiOrderedDict, self).__setitem__(key, value)