Add os_posix gyp variable, nesting variables dicts as needed to do so.

Review URL: https://codereview.appspot.com/5845050

git-svn-id: http://skia.googlecode.com/svn/trunk@3418 2bbb7eff-a529-9590-31e7-b0007b416f81

gyp/common.gypi

@@ -6,17 +6,9 @@
 # This file is automatically included by gyp_skia when building any target.
 
 {
-  # Define all variables, allowing for override in GYP_DEFINES.
-  #
-  # One such variable is 'skia_os', which we use instead of 'OS' throughout
-  # our gyp files.  We set it automatically based on 'OS', but allow the
-  # user to override it via GYP_DEFINES if they like.
-  'variables': {
-    'skia_scalar%': 'float',
-    'skia_os%': '<(OS)',
-    'skia_mesa%': 0,
-    'skia_target_arch%': 'x86',
-  },
+  'includes': [
+    'common_variables.gypi',
+  ],
 
   'target_defaults': {
 
@@ -32,7 +24,7 @@
       ],
     },
     'includes': [
-      'common_conditions.gypi'
+      'common_conditions.gypi',
     ],
     'conditions': [
       [ 'skia_scalar == "float"',

gyp/common_variables.gypi

@@ -0,0 +1,80 @@
+# Copyright 2012 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.
+
+{
+  # Get ready for the ugly...
+  #
+  # - We have to nest our variables dictionaries multiple levels deep, so that
+  #   this and other gyp files can rely on previously-set variable values in
+  #   their 'variables': { 'conditions': [] } clauses.
+  #
+  #   Example 1:
+  #   Within this file, we use the value of variable 'skia_os' to set the
+  #   value of variable 'os_posix', so 'skia_os' must be defined within a
+  #   "more inner" (enclosed) scope than 'os_posix'.
+  #
+  #   Example 2:
+  #   http://src.chromium.org/viewvc/chrome/trunk/src/third_party/libjpeg/libjpeg.gyp?revision=102306 ,
+  #   which we currently import into our build, uses the value of 'os_posix'
+  #   within the 'conditions' list in its 'variables' dict.
+  #   In order for that to work, it needs the value of 'os_posix' to have been
+  #   set within a "more inner" (enclosed) scope than its own 'variables' dict.
+  #
+  # - On the other hand, key/value pairs of a given 'variable' dict are only
+  #   inherited by:
+  #   1. directly enclosing 'variable' dicts, and
+  #   2. "sibling" 'variable' dicts (which, I guess, are combined into a single
+  #      'variable' dict during gyp processing)
+  #   and NOT inherited by "uncles" (siblings of directly enclosing 'variable'
+  #   dicts), so we have to re-define every variable at every enclosure level
+  #   within our ridiculous matryoshka doll of 'variable' dicts.  That's why
+  #   we have variable definitions like this:  'skia_os%': '<(skia_os)',
+  #
+  # See http://src.chromium.org/viewvc/chrome/trunk/src/build/common.gypi?revision=127004 ,
+  # which deals with these same constraints in a similar manner.
+  #
+  'variables': {  # level 1
+    'variables': {  # level 2
+
+      # Variables needed by conditions list within the level-2 variables dict.
+      'variables': {  # level 3
+        # We use 'skia_os' instead of 'OS' throughout our gyp files, to allow
+        # for cross-compilation (e.g. building for either MacOS or iOS on Mac).
+        # We set it automatically based on 'OS' (the host OS), but allow the
+        # user to override it via GYP_DEFINES if they like.
+        'skia_os%': '<(OS)',
+      },
+
+      # Re-define all variables defined within the level-3 'variables' dict,
+      # so that siblings of the level-2 'variables' dict can see them.
+      'skia_os%': '<(skia_os)',
+
+      'conditions': [
+        ['skia_os == "win"', {
+          'os_posix%': 0,
+        }, {
+          'os_posix%': 1,
+        }],
+      ],
+
+      'skia_scalar%': 'float',
+      'skia_mesa%': 0,
+      'skia_target_arch%': 'x86',
+    },
+
+    # Re-define all variables defined within the level-2 'variables' dict,
+    # so that siblings of the level-1 'variables' dict can see them.
+    'skia_os%': '<(skia_os)',
+    'os_posix%': '<(os_posix)',
+    'skia_scalar%': '<(skia_scalar)',
+    'skia_mesa%': '<(skia_mesa)',
+    'skia_target_arch%': '<(skia_target_arch)',
+  },
+}
+# Local Variables:
+# tab-width:2
+# indent-tabs-mode:nil
+# End:
+# vim: set expandtab tabstop=2 shiftwidth=2: