1 files changed, 78 insertions, 0 deletions
diff --git a/extras/why.py b/extras/why.py
new file mode 100644
index 00000000..1bb941f6
--- /dev/null
+++ b/extras/why.py
@@ -0,0 +1,78 @@
+#! /usr/bin/env python
+# encoding: utf-8
+# Thomas Nagy, 2010 (ita)
+
+"""
+This tool modifies the task signature scheme to store and obtain
+information about the task execution (why it must run, etc)::
+
+	def configure(conf):
+		conf.load('why')
+
+After adding the tool, a full rebuild is necessary:
+waf clean build --zones=task
+"""
+
+from waflib import Task, Utils, Logs, Errors
+
+def signature(self):
+	# compute the result one time, and suppose the scan_signature will give the good result
+	try:
+		return self.cache_sig
+	except AttributeError:
+		pass
+
+	self.m = Utils.md5()
+	self.m.update(self.hcode)
+	id_sig = self.m.digest()
+
+	# explicit deps
+	self.m = Utils.md5()
+	self.sig_explicit_deps()
+	exp_sig = self.m.digest()
+
+	# env vars
+	self.m = Utils.md5()
+	self.sig_vars()
+	var_sig = self.m.digest()
+
+	# implicit deps / scanner results
+	self.m = Utils.md5()
+	if self.scan:
+		try:
+			self.sig_implicit_deps()
+		except Errors.TaskRescan:
+			return self.signature()
+	impl_sig = self.m.digest()
+
+	ret = self.cache_sig = impl_sig + id_sig + exp_sig + var_sig
+	return ret
+
+
+Task.Task.signature = signature
+
+old = Task.Task.runnable_status
+def runnable_status(self):
+	ret = old(self)
+	if ret == Task.RUN_ME:
+		try:
+			old_sigs = self.generator.bld.task_sigs[self.uid()]
+		except (KeyError, AttributeError):
+			Logs.debug("task: task must run as no previous signature exists")
+		else:
+			new_sigs = self.cache_sig
+			def v(x):
+				return Utils.to_hex(x)
+
+			Logs.debug('Task %r', self)
+			msgs = ['* Implicit or scanner dependency', '* Task code', '* Source file, explicit or manual dependency', '* Configuration data variable']
+			tmp = 'task: -> %s: %s %s'
+			for x in range(len(msgs)):
+				l = len(Utils.SIG_NIL)
+				a = new_sigs[x*l : (x+1)*l]
+				b = old_sigs[x*l : (x+1)*l]
+				if (a != b):
+					Logs.debug(tmp, msgs[x].ljust(35), v(a), v(b))
+	return ret
+Task.Task.runnable_status = runnable_status
+