added way for user to configure shell envronment before its executed.

2 files changed, 30 insertions, 8 deletions

diff --git a/SCons/Action.py b/SCons/Action.py
index 81dc033..0110299 100644
--- a/SCons/Action.py
+++ b/SCons/Action.py
@@ -799,25 +799,25 @@ def _subproc(scons_env, cmd, error='ignore', **kw):
         if error == 'raise': raise
         # return a dummy Popen instance that only returns error
         class dummyPopen:
-            def __init__(self, e): 
+            def __init__(self, e):
                 self.exception = e
             # Add the following two to enable using the return value as a context manager
-            # for example 
+            # for example
             #    with Action._subproc(...) as po:
             #       logic here which uses po
 
-            def __enter__(self): 
+            def __enter__(self):
                 return self
 
-            def __exit__(self, *args): 
+            def __exit__(self, *args):
                 pass
 
-            def communicate(self, input=None): 
+            def communicate(self, input=None):
                 return ('', '')
 
-            def wait(self): 
+            def wait(self):
                 return -self.exception.errno
-                
+
             stdin = None
             class f:
                 def read(self): return ''
@@ -924,7 +924,7 @@ class CommandAction(_ActionAction):
 
         escape = env.get('ESCAPE', lambda x: x)
 
-        ENV = get_default_ENV(env)
+        ENV = env.get('SHELL_ENV_EXPANDER', get_default_ENV)(env)
 
         # Ensure that the ENV values are all strings:
         for key, value in ENV.items():
diff --git a/SCons/Action.xml b/SCons/Action.xml
index 0e3ef33..69781b8 100644
--- a/SCons/Action.xml
+++ b/SCons/Action.xml
@@ -200,4 +200,26 @@ in which the command should be executed.
 </summary>
 </cvar>
 
+<cvar name="SHELL_ENV_EXPANDER">
+  <summary>
+    <para>
+A function to obtain the environment dictionary which will be used
+when executing the &cv-link-SPAWN; function. This primarily give the
+user a chance to customize the shell environment for particular Actions.
+It must return a dictionary containing the environment variables as
+keys and the values as values.
+    </para>
+
+    <example_commands>
+def custom_shell_env(env):
+    </example_commands>
+
+    <para>
+      <varname>env</varname>
+The SCons construction environment from which the functionality
+shell environment can be derived from.
+    </para>
+  </summary>
+</cvar>
+
 </sconsdoc>