build: add a helper script to retreive data from a GN project

script/lib/gn.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python
+
+import subprocess
+
+from util import scoped_cwd
+
+
+class GNProject:
+  def __init__(self, out_dir):
+    self.out_dir = out_dir
+
+  def run(self, command_name, command_args):
+    with scoped_cwd(self.out_dir):
+      complete_args = ['gn', command_name, '.'] + command_args
+      return subprocess.check_output(complete_args)
+
+  def args(self):
+    return GNArgs(self)
+
+
+class GNArgs:
+  def __init__(self, project):
+    self.project = project
+
+  def _get_raw_value(self, name):
+    # E.g. 'version = "1.0.0"\n'
+    raw_output = self.project.run('args',
+                                  ['--list={}'.format(name), '--short'])
+
+    # E.g. 'version = "1.0.0"'
+    name_with_raw_value = raw_output[:-1]
+
+    # E.g. ['version', '"1.0.0"']
+    name_and_raw_value = name_with_raw_value.split(' = ')
+
+    raw_value = name_and_raw_value[1]
+    return raw_value
+
+  def get_string(self, name):
+    # Expects to get a string in double quotes, e.g. '"some_value"'.
+    raw_value = self._get_raw_value(name)
+
+    # E.g. 'some_value' (without enclosing quotes).
+    value = raw_value[1:-1]
+    return value
+
+  def get_boolean(self, name):
+    # Expects to get a 'true' or a 'false' string.
+    raw_value = self._get_raw_value(name)
+
+    if raw_value == 'true':
+      return True
+
+    if raw_value == 'false':
+      return False
+
+    return None
+
+
+def gn(out_dir):
+  return GNProject(out_dir)