This changes variable expansion so that it is recursive

pylib/gyp/__init__.py

 #!/usr/bin/python
 
 import copy
 import gyp.input
 import optparse
 import os.path
+import sets
 import shlex
 import sys
 
+# Default debug modes for GYP
+debug = sets.Set([])
+
+# List of "official" debug modes, but you can use anything you like.
+DEBUG_GENERAL = 'general'
+DEBUG_VARIABLES = 'variables'
+
+def DebugOutput(mode, message):
+  if mode in gyp.debug:
+    print "%s: %s" % (mode.upper(), message)
 
 def FindBuildFiles():
   extension = '.gyp'
   files = os.listdir(os.getcwd())
   build_files = []
   for file in files:
     if file[-len(extension):] == extension:
       build_files.append(file)
   return build_files
 
@@ skipping 71 matching lines @@
                     help='sets variable VAR to value VAL')
   parser.add_option('-f', '--format', dest='formats', action='append',
                     help='output formats to generate')
   parser.add_option('--msvs-version', dest='msvs_version',
                     help='Deprecated; use -G msvs_version=MSVS_VERSION instead')
   parser.add_option('-I', '--include', dest='includes', action='append',
                     metavar='INCLUDE',
                     help='files to include in all loaded .gyp files')
   parser.add_option('--depth', dest='depth', metavar='PATH',
                     help='set DEPTH gyp variable to a relative path to PATH')
+  parser.add_option('-d', '--debug', dest='debug', metavar='DEBUGMODE',
+                    action='append', default=[], help='turn on a debugging '
+                    'mode for debugging GYP.  Supported modes are "variables" '
+                    'and "general"')
   parser.add_option('-S', '--suffix', dest='suffix', default='',
                     help='suffix to add to generated files')
   parser.add_option('-G', dest='generator_flags', action='append', default=[],
                     metavar='FLAG=VAL', help='sets generator flag FLAG to VAL')
 
   # We read a few things from ~/.gyp, so set up a var for that.
   home_vars = ['HOME']
   if sys.platform in ('cygwin', 'win32'):
     home_vars.append('USERPROFILE')
   home = None
   for home_var in home_vars:
     home = os.getenv(home_var)
     if home != None:
       break
   home_dot_gyp = None
   if home != None:
     home_dot_gyp = os.path.join(home, '.gyp')
     if not os.path.exists(home_dot_gyp):
       home_dot_gyp = None
 
   # TODO(thomasvl): add support for ~/.gyp/defaults
 
   (options, build_files) = parser.parse_args(args)
 
+  gyp.debug = sets.Set(options.debug)
+
+  # Do an extra check to avoid work when we're not debugging.
+  if DEBUG_GENERAL in gyp.debug:
+    DebugOutput(DEBUG_GENERAL, 'running with these options:')
+    for (option, value) in options.__dict__.items():
+      if isinstance(value, basestring):
+        DebugOutput(DEBUG_GENERAL, "  %s: '%s'" % (option, value))
+      else:
+        DebugOutput(DEBUG_GENERAL, "  %s: %s" % (option, str(value)))
+
   if not options.formats:
     # If no format was given on the command line, then check the env variable.
     generate_formats = os.environ.get('GYP_GENERATORS', [])
     if generate_formats:
       generate_formats = shlex.split(generate_formats)
     if generate_formats:
       options.formats = generate_formats
     else:
       # Nothing in the variable, default based on platform.
       options.formats = [ {'darwin':   'xcode',
@@ skipping 64 matching lines @@
     includes.extend(options.includes)
 
   # Generator flags should be prefixed with the target generator since they
   # are global across all generator runs.
   gen_flags = os.environ.get('GYP_GENERATOR_FLAGS', [])
   if gen_flags:
     gen_flags = shlex.split(gen_flags)
   if options.generator_flags:
     gen_flags += options.generator_flags
   generator_flags = NameValueListToDict(gen_flags)
-  
+
   # TODO: Remove this and the option after we've gotten folks to move to the
   # generator flag.
   if options.msvs_version:
     print >>sys.stderr, \
       'DEPRECATED: Use generator flag (-G msvs_version=' + \
       options.msvs_version + ') instead of --msvs-version=' + \
       options.msvs_version
     generator_flags['msvs_version'] = options.msvs_version
 
   # Generate all requested formats (use a set in case we got one format request
@@ skipping 17 matching lines @@
     # need to have dependencies defined before dependents reference them should
     # generate targets in the order specified in flat_list.
     generator.GenerateOutput(flat_list, targets, data, params)
 
   # Done
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))