Support default Options values of None. (Gary Oberbrunner)

4 files changed, 27 insertions, 3 deletions

diff --git a/doc/man/scons.1 b/doc/man/scons.1
index b94d680..fdfae69 100644
--- a/doc/man/scons.1
+++ b/doc/man/scons.1
@@ -7104,7 +7104,13 @@ is the name of the variable.
 .I help 
 is the help text for the variable.
 .I default 
-is the default value of the variable.
+is the default value of the variable;
+if the default value is
+.B None
+and there is no explicit value specified,
+the construction variable will
+.I not
+be added to the construction environment.
 .I validator
 is called to validate the value of the variable, and should take three
 arguments: key, value, and environment
diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index df34c85..6747261 100644
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -150,6 +150,10 @@ RELEASE 0.97 - XXX
   - Allow Tool specifications to be passed a dictionary of keyword
     arguments.
 
+  - Support an Options default value of None, in which case the variable
+    will not be added to the construction environment unless it's set
+    explicitly by the user or from an Options file.
+
   From Chris Pawling:
 
   - Have the linkloc tool use $MSVS_VERSION to select the Microsoft
diff --git a/src/engine/SCons/Options/OptionsTests.py b/src/engine/SCons/Options/OptionsTests.py
index afcb4d3..4248dc3 100644
--- a/src/engine/SCons/Options/OptionsTests.py
+++ b/src/engine/SCons/Options/OptionsTests.py
@@ -244,7 +244,21 @@ class OptionsTestCase(unittest.TestCase):
         env = Environment()
         opts.Update(env, {})
         assert not env.has_key('ANSWER')
-        
+
+        # Test that a default value of None is all right.
+        test = TestSCons.TestSCons()
+        file = test.workpath('custom.py')
+        opts = SCons.Options.Options(file)
+
+        opts.Add('ANSWER',
+                 "This is the answer",
+                 None,
+                 check)
+
+        env = Environment()
+        opts.Update(env, {})
+        assert not env.has_key('ANSWER')
+
     def test_args(self):
         """Test updating an Environment with arguments overridden"""
 
diff --git a/src/engine/SCons/Options/__init__.py b/src/engine/SCons/Options/__init__.py
index 521171c..fdaee92 100644
--- a/src/engine/SCons/Options/__init__.py
+++ b/src/engine/SCons/Options/__init__.py
@@ -165,7 +165,7 @@ class Options:
 
         # Finally validate the values:
         for option in self.options:
-            if option.validator:
+            if option.validator and values.has_key(option.key):
                 option.validator(option.key, env.subst('${%s}'%option.key), env)
 
     def Save(self, filename, env):