Port tools/message.jam.

[SVN r64708]

v2/tools/builtin.py

@@ -715,3 +715,4 @@ get_manager().projects().add_rule("variant", variant)
 
 import stage
 import symlink
+import message

v2/tools/message.py

@@ -0,0 +1,46 @@
+# Status: ported.
+# Base revision: 64488.
+#
+# Copyright 2008, 2010 Vladimir Prus
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
+
+# Defines main target type 'message', that prints a message when built for the
+# first time.
+
+import b2.build.targets as targets
+import b2.build.property_set as property_set
+
+from b2.manager import get_manager
+
+class MessageTargetClass(targets.BasicTarget):
+
+    def __init__(self, name, project, *args):
+
+        targets.BasicTarget.__init__(self, name, project, [])
+        self.args = args
+        self.built = False
+
+    def construct(self, name, sources, ps):
+
+        if not self.built:
+            for arg in self.args:
+                if type(arg) == type([]):
+                    arg = " ".join(arg)                
+                print arg
+            self.built = True
+
+        return (property_set.empty(), [])
+
+def message(name, *args):
+
+    if type(name) == type([]):
+        name = name[0]
+
+    t = get_manager().targets()
+    
+    project = get_manager().projects().current()
+        
+    return t.main_target_alternative(MessageTargetClass(*((name, project) + args)))
+
+get_manager().projects().add_rule("message", message)