Speed up SCons execution by creating DefaultEnvironment for

SCons.SConf.CreateConfigHBuilder only if necessary.

2 files changed, 14 insertions, 4 deletions

diff --git a/src/engine/SCons/SConf.py b/src/engine/SCons/SConf.py
index 6cc8de8..dd93269 100644
--- a/src/engine/SCons/SConf.py
+++ b/src/engine/SCons/SConf.py
@@ -119,16 +119,22 @@ def _createConfigH(target, source, env):
 def _stringConfigH(target, source, env):
     return "scons: Configure: creating " + str(target[0])
 
-def CreateConfigHBuilder(env):
-    """Called just before the building targets phase begins."""
+
+def NeedConfigHBuilder():
     if len(_ac_config_hs) == 0:
-        return
+       return False
+    else:
+       return True
+
+def CreateConfigHBuilder(env):
+    """Called if necessary just before the building targets phase begins."""
     action = SCons.Action.Action(_createConfigH,
                                  _stringConfigH)
     sconfigHBld = SCons.Builder.Builder(action=action)
     env.Append( BUILDERS={'SConfigHBuilder':sconfigHBld} )
     for k in _ac_config_hs.keys():
         env.SConfigHBuilder(k, env.Value(_ac_config_hs[k]))
+
     
 class SConfWarning(SCons.Warnings.Warning):
     pass
diff --git a/src/engine/SCons/Script/Main.py b/src/engine/SCons/Script/Main.py
index d4dd229..439b869 100644
--- a/src/engine/SCons/Script/Main.py
+++ b/src/engine/SCons/Script/Main.py
@@ -1031,7 +1031,11 @@ def _main(parser):
                             msg % (deprecated_version_string, python_version_string()))
 
     if not options.help:
-        SCons.SConf.CreateConfigHBuilder(SCons.Defaults.DefaultEnvironment())
+        # [ ] Clarify why we need to create Builder here at all, and
+        #     why it is created in DefaultEnvironment
+        # https://bitbucket.org/scons/scons/commits/d27a548aeee8ad5e67ea75c2d19a7d305f784e30
+        if SCons.SConf.NeedConfigHBuilder():
+            SCons.SConf.CreateConfigHBuilder(SCons.Defaults.DefaultEnvironment())
 
     # Now re-parse the command-line options (any to the left of a '--'
     # argument, that is) with any user-defined command-line options that