Improve the definition of static link tasks

waflib/Tools/ccroot.py

@@ -224,14 +224,24 @@ class link_task(Task.Task):
 class stlink_task(link_task):
 	"""
 	Base for static link tasks, which use *ar* most of the time.
-	The target is always removed before being written.
 	"""
-	run_str = '${AR} ${ARFLAGS} ${AR_TGT_F}${TGT} ${AR_SRC_F}${SRC}'
+	run_str = [
+		lambda task: task.remove_before_build(),
+		'${AR} ${ARFLAGS} ${AR_TGT_F}${TGT} ${AR_SRC_F}${SRC}'
+	]
 
 	chmod   = Utils.O644
 	"""Default installation mode for the static libraries"""
 
+	def remove_before_build(self):
+		"Remove the library before building it"
+		try:
+			os.remove(self.outputs[0].abspath())
+		except OSError:
+			pass
+
 def rm_tgt(cls):
+	# TODO obsolete code, remove in waf 2.2
 	old = cls.run
 	def wrap(self):
 		try:
@@ -240,7 +250,6 @@ def rm_tgt(cls):
 			pass
 		return old(self)
 	setattr(cls, 'run', wrap)
-rm_tgt(stlink_task)
 
 @feature('skip_stlib_link_deps')
 @before_method('process_use')