gyp_skia: make default GYP_GENERATORS for each platform explicit

gyp_skia

 #!/usr/bin/python
 
 # Copyright 2011 The Android Open Source Project
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script is a wrapper which invokes gyp with the correct --depth argument,
 # and supports the automatic regeneration of build files if all.gyp is
 # changed (Linux-only).
@@ skipping 10 matching lines @@
 gyp_source_dir = os.path.join(script_dir, 'third_party', 'externals', 'gyp')
 
 # Directory within which we can find most of Skia's gyp configuration files.
 gyp_config_dir = os.path.join(script_dir, 'gyp')
 
 # Ensure we import our current gyp source's module, not any version
 # pre-installed in your PYTHONPATH.
 sys.path.insert(0, os.path.join(gyp_source_dir, 'pylib'))
 import gyp
 
+ENVVAR_GYP_GENERATORS = 'GYP_GENERATORS'
+
+
 def additional_include_files(args=[]):
   # Determine the include files specified on the command line.
   # This doesn't cover all the different option formats you can use,
   # but it's mainly intended to avoid duplicating flags on the automatic
   # makefile regeneration which only uses this format.
   specified_includes = set()
   for arg in args:
     if arg.startswith('-I') and len(arg) > 2:
       specified_includes.add(os.path.realpath(arg[2:]))
 
@@ skipping 14 matching lines @@
 # be written.
 def get_output_dir():
 
   # SKIA_OUT can be any directory either as a child of the standard out/
   # directory or any given location on the file system (e.g. /tmp/skia)
   output_dir = os.getenv('SKIA_OUT')
 
   if not output_dir:
     return os.path.join(os.path.abspath(script_dir), 'out')
 
-  if (sys.platform.startswith('darwin') and 
-      (not os.getenv('GYP_GENERATORS') or 
-       'xcode' in os.getenv('GYP_GENERATORS'))):
+  if (sys.platform.startswith('darwin') and
+      (not os.getenv(ENVVAR_GYP_GENERATORS) or
+       'xcode' in os.getenv(ENVVAR_GYP_GENERATORS))):
     print 'ERROR: variable SKIA_OUT is not valid on Mac (using xcodebuild)'
     sys.exit(-1);
 
   if os.path.isabs(output_dir):
     return output_dir
   else:
     return os.path.join(os.path.abspath(script_dir), output_dir)
 
 
 if __name__ == '__main__':
   args = sys.argv[1:]
 
+  if not os.getenv(ENVVAR_GYP_GENERATORS):
+    print ('%s environment variable not set, using default' %
+           ENVVAR_GYP_GENERATORS)
+    if sys.platform.startswith('darwin'):
+      default_gyp_generators = 'xcode'
+    elif sys.platform.startswith('win'):
+      default_gyp_generators = 'msvs'
+    elif sys.platform.startswith('cygwin'):
+      default_gyp_generators = 'msvs'
+    else:
+      default_gyp_generators = 'make'
+    os.environ[ENVVAR_GYP_GENERATORS] = default_gyp_generators
+  print '%s is "%s"' % (ENVVAR_GYP_GENERATORS, os.getenv(ENVVAR_GYP_GENERATORS))
+
   # Set CWD to the directory containing this script.
   # This allows us to launch it from other directories, in spite of gyp's
   # finickyness about the current working directory.
   # See http://b.corp.google.com/issue?id=5019517 ('Linux make build
   # (from out dir) no longer runs skia_gyp correctly')
   os.chdir(os.path.abspath(script_dir))
 
   # This could give false positives since it doesn't actually do real option
   # parsing.  Oh well.
   gyp_file_specified = False
@@ skipping 19 matching lines @@
   args.extend(['-Goutput_dir=.'])
 
   # By default, we build 'most' instead of 'all' or 'everything'. See skia.gyp.
   args.extend(['-Gdefault_target=most'])
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Off we go...
   sys.exit(gyp.main(args))