Merge commit 'c2b0355b0de23f6ec83b5fa5be038bcce208e26f' as 'waflib'

1 files changed, 1394 insertions, 0 deletions

diff --git a/waflib/Task.py b/waflib/Task.py
new file mode 100644
index 00000000..0fc449d4
--- /dev/null
+++ b/waflib/Task.py
@@ -0,0 +1,1394 @@
+#!/usr/bin/env python
+# encoding: utf-8
+# Thomas Nagy, 2005-2018 (ita)
+
+"""
+Tasks represent atomic operations such as processes.
+"""
+
+import os, re, sys, tempfile, traceback
+from waflib import Utils, Logs, Errors
+
+# task states
+NOT_RUN = 0
+"""The task was not executed yet"""
+
+MISSING = 1
+"""The task has been executed but the files have not been created"""
+
+CRASHED = 2
+"""The task execution returned a non-zero exit status"""
+
+EXCEPTION = 3
+"""An exception occurred in the task execution"""
+
+CANCELED = 4
+"""A dependency for the task is missing so it was cancelled"""
+
+SKIPPED = 8
+"""The task did not have to be executed"""
+
+SUCCESS = 9
+"""The task was successfully executed"""
+
+ASK_LATER = -1
+"""The task is not ready to be executed"""
+
+SKIP_ME = -2
+"""The task does not need to be executed"""
+
+RUN_ME = -3
+"""The task must be executed"""
+
+CANCEL_ME = -4
+"""The task cannot be executed because of a dependency problem"""
+
+COMPILE_TEMPLATE_SHELL = '''
+def f(tsk):
+	env = tsk.env
+	gen = tsk.generator
+	bld = gen.bld
+	cwdx = tsk.get_cwd()
+	p = env.get_flat
+	tsk.last_cmd = cmd = \'\'\' %s \'\'\' % s
+	return tsk.exec_command(cmd, cwd=cwdx, env=env.env or None)
+'''
+
+COMPILE_TEMPLATE_NOSHELL = '''
+def f(tsk):
+	env = tsk.env
+	gen = tsk.generator
+	bld = gen.bld
+	cwdx = tsk.get_cwd()
+	def to_list(xx):
+		if isinstance(xx, str): return [xx]
+		return xx
+	def merge(lst1, lst2):
+		if lst1 and lst2:
+			return lst1[:-1] + [lst1[-1] + lst2[0]] + lst2[1:]
+		return lst1 + lst2
+	lst = []
+	%s
+	if '' in lst:
+		lst = [x for x in lst if x]
+	tsk.last_cmd = lst
+	return tsk.exec_command(lst, cwd=cwdx, env=env.env or None)
+'''
+
+COMPILE_TEMPLATE_SIG_VARS = '''
+def f(tsk):
+	super(tsk.__class__, tsk).sig_vars()
+	env = tsk.env
+	gen = tsk.generator
+	bld = gen.bld
+	cwdx = tsk.get_cwd()
+	p = env.get_flat
+	buf = []
+	%s
+	tsk.m.update(repr(buf).encode())
+'''
+
+classes = {}
+"""
+The metaclass :py:class:`waflib.Task.store_task_type` stores all class tasks
+created by user scripts or Waf tools to this dict. It maps class names to class objects.
+"""
+
+class store_task_type(type):
+	"""
+	Metaclass: store the task classes into the dict pointed by the
+	class attribute 'register' which defaults to :py:const:`waflib.Task.classes`,
+
+	The attribute 'run_str' is compiled into a method 'run' bound to the task class.
+	"""
+	def __init__(cls, name, bases, dict):
+		super(store_task_type, cls).__init__(name, bases, dict)
+		name = cls.__name__
+
+		if name != 'evil' and name != 'Task':
+			if getattr(cls, 'run_str', None):
+				# if a string is provided, convert it to a method
+				(f, dvars) = compile_fun(cls.run_str, cls.shell)
+				cls.hcode = Utils.h_cmd(cls.run_str)
+				cls.orig_run_str = cls.run_str
+				# change the name of run_str or it is impossible to subclass with a function
+				cls.run_str = None
+				cls.run = f
+				# process variables
+				cls.vars = list(set(cls.vars + dvars))
+				cls.vars.sort()
+				if cls.vars:
+					fun = compile_sig_vars(cls.vars)
+					if fun:
+						cls.sig_vars = fun
+			elif getattr(cls, 'run', None) and not 'hcode' in cls.__dict__:
+				# getattr(cls, 'hcode') would look in the upper classes
+				cls.hcode = Utils.h_cmd(cls.run)
+
+			# be creative
+			getattr(cls, 'register', classes)[name] = cls
+
+evil = store_task_type('evil', (object,), {})
+"Base class provided to avoid writing a metaclass, so the code can run in python 2.6 and 3.x unmodified"
+
+class Task(evil):
+	"""
+	Task objects represents actions to perform such as commands to execute by calling the `run` method.
+
+	Detecting when to execute a task occurs in the method :py:meth:`waflib.Task.Task.runnable_status`.
+
+	Detecting which tasks to execute is performed through a hash value returned by
+	:py:meth:`waflib.Task.Task.signature`. The task signature is persistent from build to build.
+	"""
+	vars = []
+	"""ConfigSet variables that should trigger a rebuild (class attribute used for :py:meth:`waflib.Task.Task.sig_vars`)"""
+
+	always_run = False
+	"""Specify whether task instances must always be executed or not (class attribute)"""
+
+	shell = False
+	"""Execute the command with the shell (class attribute)"""
+
+	color = 'GREEN'
+	"""Color for the console display, see :py:const:`waflib.Logs.colors_lst`"""
+
+	ext_in = []
+	"""File extensions that objects of this task class may use"""
+
+	ext_out = []
+	"""File extensions that objects of this task class may create"""
+
+	before = []
+	"""List of task class names to execute before instances of this class"""
+
+	after = []
+	"""List of task class names to execute after instances of this class"""
+
+	hcode = Utils.SIG_NIL
+	"""String representing an additional hash for the class representation"""
+
+	keep_last_cmd = False
+	"""Whether to keep the last command executed on the instance after execution.
+	This may be useful for certain extensions but it can a lot of memory.
+	"""
+
+	weight = 0
+	"""Optional weight to tune the priority for task instances.
+	The higher, the earlier. The weight only applies to single task objects."""
+
+	tree_weight = 0
+	"""Optional weight to tune the priority of task instances and whole subtrees.
+	The higher, the earlier."""
+
+	prio_order = 0
+	"""Priority order set by the scheduler on instances during the build phase.
+	You most likely do not need to set it.
+	"""
+
+	__slots__ = ('hasrun', 'generator', 'env', 'inputs', 'outputs', 'dep_nodes', 'run_after')
+
+	def __init__(self, *k, **kw):
+		self.hasrun = NOT_RUN
+		try:
+			self.generator = kw['generator']
+		except KeyError:
+			self.generator = self
+
+		self.env = kw['env']
+		""":py:class:`waflib.ConfigSet.ConfigSet` object (make sure to provide one)"""
+
+		self.inputs  = []
+		"""List of input nodes, which represent the files used by the task instance"""
+
+		self.outputs = []
+		"""List of output nodes, which represent the files created by the task instance"""
+
+		self.dep_nodes = []
+		"""List of additional nodes to depend on"""
+
+		self.run_after = set()
+		"""Set of tasks that must be executed before this one"""
+
+	def __lt__(self, other):
+		return self.priority() > other.priority()
+	def __le__(self, other):
+		return self.priority() >= other.priority()
+	def __gt__(self, other):
+		return self.priority() < other.priority()
+	def __ge__(self, other):
+		return self.priority() <= other.priority()
+
+	def get_cwd(self):
+		"""
+		:return: current working directory
+		:rtype: :py:class:`waflib.Node.Node`
+		"""
+		bld = self.generator.bld
+		ret = getattr(self, 'cwd', None) or getattr(bld, 'cwd', bld.bldnode)
+		if isinstance(ret, str):
+			if os.path.isabs(ret):
+				ret = bld.root.make_node(ret)
+			else:
+				ret = self.generator.path.make_node(ret)
+		return ret
+
+	def quote_flag(self, x):
+		"""
+		Surround a process argument by quotes so that a list of arguments can be written to a file
+
+		:param x: flag
+		:type x: string
+		:return: quoted flag
+		:rtype: string
+		"""
+		old = x
+		if '\\' in x:
+			x = x.replace('\\', '\\\\')
+		if '"' in x:
+			x = x.replace('"', '\\"')
+		if old != x or ' ' in x or '\t' in x or "'" in x:
+			x = '"%s"' % x
+		return x
+
+	def priority(self):
+		"""
+		Priority of execution; the higher, the earlier
+
+		:return: the priority value
+		:rtype: a tuple of numeric values
+		"""
+		return (self.weight + self.prio_order, - getattr(self.generator, 'tg_idx_count', 0))
+
+	def split_argfile(self, cmd):
+		"""
+		Splits a list of process commands into the executable part and its list of arguments
+
+		:return: a tuple containing the executable first and then the rest of arguments
+		:rtype: tuple
+		"""
+		return ([cmd[0]], [self.quote_flag(x) for x in cmd[1:]])
+
+	def exec_command(self, cmd, **kw):
+		"""
+		Wrapper for :py:meth:`waflib.Context.Context.exec_command`.
+		This version set the current working directory (``build.variant_dir``),
+		applies PATH settings (if self.env.PATH is provided), and can run long
+		commands through a temporary ``@argfile``.
+
+		:param cmd: process command to execute
+		:type cmd: list of string (best) or string (process will use a shell)
+		:return: the return code
+		:rtype: int
+
+		Optional parameters:
+
+		#. cwd: current working directory (Node or string)
+		#. stdout: set to None to prevent waf from capturing the process standard output
+		#. stderr: set to None to prevent waf from capturing the process standard error
+		#. timeout: timeout value (Python 3)
+		"""
+		if not 'cwd' in kw:
+			kw['cwd'] = self.get_cwd()
+
+		if hasattr(self, 'timeout'):
+			kw['timeout'] = self.timeout
+
+		if self.env.PATH:
+			env = kw['env'] = dict(kw.get('env') or self.env.env or os.environ)
+			env['PATH'] = self.env.PATH if isinstance(self.env.PATH, str) else os.pathsep.join(self.env.PATH)
+
+		if hasattr(self, 'stdout'):
+			kw['stdout'] = self.stdout
+		if hasattr(self, 'stderr'):
+			kw['stderr'] = self.stderr
+
+		# workaround for command line length limit:
+		# http://support.microsoft.com/kb/830473
+		if not isinstance(cmd, str) and (len(repr(cmd)) >= 8192 if Utils.is_win32 else len(cmd) > 200000):
+			cmd, args = self.split_argfile(cmd)
+			try:
+				(fd, tmp) = tempfile.mkstemp()
+				os.write(fd, '\r\n'.join(args).encode())
+				os.close(fd)
+				if Logs.verbose:
+					Logs.debug('argfile: @%r -> %r', tmp, args)
+				return self.generator.bld.exec_command(cmd + ['@' + tmp], **kw)
+			finally:
+				try:
+					os.remove(tmp)
+				except OSError:
+					# anti-virus and indexers can keep files open -_-
+					pass
+		else:
+			return self.generator.bld.exec_command(cmd, **kw)
+
+	def process(self):
+		"""
+		Runs the task and handles errors
+
+		:return: 0 or None if everything is fine
+		:rtype: integer
+		"""
+		# remove the task signature immediately before it is executed
+		# so that the task will be executed again in case of failure
+		try:
+			del self.generator.bld.task_sigs[self.uid()]
+		except KeyError:
+			pass
+
+		try:
+			ret = self.run()
+		except Exception:
+			self.err_msg = traceback.format_exc()
+			self.hasrun = EXCEPTION
+		else:
+			if ret:
+				self.err_code = ret
+				self.hasrun = CRASHED
+			else:
+				try:
+					self.post_run()
+				except Errors.WafError:
+					pass
+				except Exception:
+					self.err_msg = traceback.format_exc()
+					self.hasrun = EXCEPTION
+				else:
+					self.hasrun = SUCCESS
+
+		if self.hasrun != SUCCESS and self.scan:
+			# rescan dependencies on next run
+			try:
+				del self.generator.bld.imp_sigs[self.uid()]
+			except KeyError:
+				pass
+
+	def log_display(self, bld):
+		"Writes the execution status on the context logger"
+		if self.generator.bld.progress_bar == 3:
+			return
+
+		s = self.display()
+		if s:
+			if bld.logger:
+				logger = bld.logger
+			else:
+				logger = Logs
+
+			if self.generator.bld.progress_bar == 1:
+				c1 = Logs.colors.cursor_off
+				c2 = Logs.colors.cursor_on
+				logger.info(s, extra={'stream': sys.stderr, 'terminator':'', 'c1': c1, 'c2' : c2})
+			else:
+				logger.info(s, extra={'terminator':'', 'c1': '', 'c2' : ''})
+
+	def display(self):
+		"""
+		Returns an execution status for the console, the progress bar, or the IDE output.
+
+		:rtype: string
+		"""
+		col1 = Logs.colors(self.color)
+		col2 = Logs.colors.NORMAL
+		master = self.generator.bld.producer
+
+		def cur():
+			# the current task position, computed as late as possible
+			return master.processed - master.ready.qsize()
+
+		if self.generator.bld.progress_bar == 1:
+			return self.generator.bld.progress_line(cur(), master.total, col1, col2)
+
+		if self.generator.bld.progress_bar == 2:
+			ela = str(self.generator.bld.timer)
+			try:
+				ins  = ','.join([n.name for n in self.inputs])
+			except AttributeError:
+				ins = ''
+			try:
+				outs = ','.join([n.name for n in self.outputs])
+			except AttributeError:
+				outs = ''
+			return '|Total %s|Current %s|Inputs %s|Outputs %s|Time %s|\n' % (master.total, cur(), ins, outs, ela)
+
+		s = str(self)
+		if not s:
+			return None
+
+		total = master.total
+		n = len(str(total))
+		fs = '[%%%dd/%%%dd] %%s%%s%%s%%s\n' % (n, n)
+		kw = self.keyword()
+		if kw:
+			kw += ' '
+		return fs % (cur(), total, kw, col1, s, col2)
+
+	def hash_constraints(self):
+		"""
+		Identifies a task type for all the constraints relevant for the scheduler: precedence, file production
+
+		:return: a hash value
+		:rtype: string
+		"""
+		return (tuple(self.before), tuple(self.after), tuple(self.ext_in), tuple(self.ext_out), self.__class__.__name__, self.hcode)
+
+	def format_error(self):
+		"""
+		Returns an error message to display the build failure reasons
+
+		:rtype: string
+		"""
+		if Logs.verbose:
+			msg = ': %r\n%r' % (self, getattr(self, 'last_cmd', ''))
+		else:
+			msg = ' (run with -v to display more information)'
+		name = getattr(self.generator, 'name', '')
+		if getattr(self, "err_msg", None):
+			return self.err_msg
+		elif not self.hasrun:
+			return 'task in %r was not executed for some reason: %r' % (name, self)
+		elif self.hasrun == CRASHED:
+			try:
+				return ' -> task in %r failed with exit status %r%s' % (name, self.err_code, msg)
+			except AttributeError:
+				return ' -> task in %r failed%s' % (name, msg)
+		elif self.hasrun == MISSING:
+			return ' -> missing files in %r%s' % (name, msg)
+		elif self.hasrun == CANCELED:
+			return ' -> %r canceled because of missing dependencies' % name
+		else:
+			return 'invalid status for task in %r: %r' % (name, self.hasrun)
+
+	def colon(self, var1, var2):
+		"""
+		Enable scriptlet expressions of the form ${FOO_ST:FOO}
+		If the first variable (FOO_ST) is empty, then an empty list is returned
+
+		The results will be slightly different if FOO_ST is a list, for example::
+
+			env.FOO    = ['p1', 'p2']
+			env.FOO_ST = '-I%s'
+			# ${FOO_ST:FOO} returns
+			['-Ip1', '-Ip2']
+
+			env.FOO_ST = ['-a', '-b']
+			# ${FOO_ST:FOO} returns
+			['-a', '-b', 'p1', '-a', '-b', 'p2']
+		"""
+		tmp = self.env[var1]
+		if not tmp:
+			return []
+
+		if isinstance(var2, str):
+			it = self.env[var2]
+		else:
+			it = var2
+		if isinstance(tmp, str):
+			return [tmp % x for x in it]
+		else:
+			lst = []
+			for y in it:
+				lst.extend(tmp)
+				lst.append(y)
+			return lst
+
+	def __str__(self):
+		"string to display to the user"
+		name = self.__class__.__name__
+		if self.outputs:
+			if name.endswith(('lib', 'program')) or not self.inputs:
+				node = self.outputs[0]
+				return node.path_from(node.ctx.launch_node())
+		if not (self.inputs or self.outputs):
+			return self.__class__.__name__
+		if len(self.inputs) == 1:
+			node = self.inputs[0]
+			return node.path_from(node.ctx.launch_node())
+
+		src_str = ' '.join([a.path_from(a.ctx.launch_node()) for a in self.inputs])
+		tgt_str = ' '.join([a.path_from(a.ctx.launch_node()) for a in self.outputs])
+		if self.outputs:
+			sep = ' -> '
+		else:
+			sep = ''
+		return '%s: %s%s%s' % (self.__class__.__name__, src_str, sep, tgt_str)
+
+	def keyword(self):
+		"Display keyword used to prettify the console outputs"
+		name = self.__class__.__name__
+		if name.endswith(('lib', 'program')):
+			return 'Linking'
+		if len(self.inputs) == 1 and len(self.outputs) == 1:
+			return 'Compiling'
+		if not self.inputs:
+			if self.outputs:
+				return 'Creating'
+			else:
+				return 'Running'
+		return 'Processing'
+
+	def __repr__(self):
+		"for debugging purposes"
+		try:
+			ins = ",".join([x.name for x in self.inputs])
+			outs = ",".join([x.name for x in self.outputs])
+		except AttributeError:
+			ins = ",".join([str(x) for x in self.inputs])
+			outs = ",".join([str(x) for x in self.outputs])
+		return "".join(['\n\t{task %r: ' % id(self), self.__class__.__name__, " ", ins, " -> ", outs, '}'])
+
+	def uid(self):
+		"""
+		Returns an identifier used to determine if tasks are up-to-date. Since the
+		identifier will be stored between executions, it must be:
+
+			- unique for a task: no two tasks return the same value (for a given build context)
+			- the same for a given task instance
+
+		By default, the node paths, the class name, and the function are used
+		as inputs to compute a hash.
+
+		The pointer to the object (python built-in 'id') will change between build executions,
+		and must be avoided in such hashes.
+
+		:return: hash value
+		:rtype: string
+		"""
+		try:
+			return self.uid_
+		except AttributeError:
+			m = Utils.md5(self.__class__.__name__)
+			up = m.update
+			for x in self.inputs + self.outputs:
+				up(x.abspath())
+			self.uid_ = m.digest()
+			return self.uid_
+
+	def set_inputs(self, inp):
+		"""
+		Appends the nodes to the *inputs* list
+
+		:param inp: input nodes
+		:type inp: node or list of nodes
+		"""
+		if isinstance(inp, list):
+			self.inputs += inp
+		else:
+			self.inputs.append(inp)
+
+	def set_outputs(self, out):
+		"""
+		Appends the nodes to the *outputs* list
+
+		:param out: output nodes
+		:type out: node or list of nodes
+		"""
+		if isinstance(out, list):
+			self.outputs += out
+		else:
+			self.outputs.append(out)
+
+	def set_run_after(self, task):
+		"""
+		Run this task only after the given *task*.
+
+		Calling this method from :py:meth:`waflib.Task.Task.runnable_status` may cause
+		build deadlocks; see :py:meth:`waflib.Tools.fc.fc.runnable_status` for details.
+
+		:param task: task
+		:type task: :py:class:`waflib.Task.Task`
+		"""
+		assert isinstance(task, Task)
+		self.run_after.add(task)
+
+	def signature(self):
+		"""
+		Task signatures are stored between build executions, they are use to track the changes
+		made to the input nodes (not to the outputs!). The signature hashes data from various sources:
+
+		* explicit dependencies: files listed in the inputs (list of node objects) :py:meth:`waflib.Task.Task.sig_explicit_deps`
+		* implicit dependencies: list of nodes returned by scanner methods (when present) :py:meth:`waflib.Task.Task.sig_implicit_deps`
+		* hashed data: variables/values read from task.vars/task.env :py:meth:`waflib.Task.Task.sig_vars`
+
+		If the signature is expected to give a different result, clear the cache kept in ``self.cache_sig``::
+
+			from waflib import Task
+			class cls(Task.Task):
+				def signature(self):
+					sig = super(Task.Task, self).signature()
+					delattr(self, 'cache_sig')
+					return super(Task.Task, self).signature()
+
+		:return: the signature value
+		:rtype: string or bytes
+		"""
+		try:
+			return self.cache_sig
+		except AttributeError:
+			pass
+
+		self.m = Utils.md5(self.hcode)
+
+		# explicit deps
+		self.sig_explicit_deps()
+
+		# env vars
+		self.sig_vars()
+
+		# implicit deps / scanner results
+		if self.scan:
+			try:
+				self.sig_implicit_deps()
+			except Errors.TaskRescan:
+				return self.signature()
+
+		ret = self.cache_sig = self.m.digest()
+		return ret
+
+	def runnable_status(self):
+		"""
+		Returns the Task status
+
+		:return: a task state in :py:const:`waflib.Task.RUN_ME`,
+			:py:const:`waflib.Task.SKIP_ME`, :py:const:`waflib.Task.CANCEL_ME` or :py:const:`waflib.Task.ASK_LATER`.
+		:rtype: int
+		"""
+		bld = self.generator.bld
+		if bld.is_install < 0:
+			return SKIP_ME
+
+		for t in self.run_after:
+			if not t.hasrun:
+				return ASK_LATER
+			elif t.hasrun < SKIPPED:
+				# a dependency has an error
+				return CANCEL_ME
+
+		# first compute the signature
+		try:
+			new_sig = self.signature()
+		except Errors.TaskNotReady:
+			return ASK_LATER
+
+		# compare the signature to a signature computed previously
+		key = self.uid()
+		try:
+			prev_sig = bld.task_sigs[key]
+		except KeyError:
+			Logs.debug('task: task %r must run: it was never run before or the task code changed', self)
+			return RUN_ME
+
+		if new_sig != prev_sig:
+			Logs.debug('task: task %r must run: the task signature changed', self)
+			return RUN_ME
+
+		# compare the signatures of the outputs
+		for node in self.outputs:
+			sig = bld.node_sigs.get(node)
+			if not sig:
+				Logs.debug('task: task %r must run: an output node has no signature', self)
+				return RUN_ME
+			if sig != key:
+				Logs.debug('task: task %r must run: an output node was produced by another task', self)
+				return RUN_ME
+			if not node.exists():
+				Logs.debug('task: task %r must run: an output node does not exist', self)
+				return RUN_ME
+
+		return (self.always_run and RUN_ME) or SKIP_ME
+
+	def post_run(self):
+		"""
+		Called after successful execution to record that the task has run by
+		updating the entry in :py:attr:`waflib.Build.BuildContext.task_sigs`.
+		"""
+		bld = self.generator.bld
+		for node in self.outputs:
+			if not node.exists():
+				self.hasrun = MISSING
+				self.err_msg = '-> missing file: %r' % node.abspath()
+				raise Errors.WafError(self.err_msg)
+			bld.node_sigs[node] = self.uid() # make sure this task produced the files in question
+		bld.task_sigs[self.uid()] = self.signature()
+		if not self.keep_last_cmd:
+			try:
+				del self.last_cmd
+			except AttributeError:
+				pass
+
+	def sig_explicit_deps(self):
+		"""
+		Used by :py:meth:`waflib.Task.Task.signature`; it hashes :py:attr:`waflib.Task.Task.inputs`
+		and :py:attr:`waflib.Task.Task.dep_nodes` signatures.
+		"""
+		bld = self.generator.bld
+		upd = self.m.update
+
+		# the inputs
+		for x in self.inputs + self.dep_nodes:
+			upd(x.get_bld_sig())
+
+		# manual dependencies, they can slow down the builds
+		if bld.deps_man:
+			additional_deps = bld.deps_man
+			for x in self.inputs + self.outputs:
+				try:
+					d = additional_deps[x]
+				except KeyError:
+					continue
+
+				for v in d:
+					try:
+						v = v.get_bld_sig()
+					except AttributeError:
+						if hasattr(v, '__call__'):
+							v = v() # dependency is a function, call it
+					upd(v)
+
+	def sig_deep_inputs(self):
+		"""
+		Enable rebuilds on input files task signatures. Not used by default.
+
+		Example: hashes of output programs can be unchanged after being re-linked,
+		despite the libraries being different. This method can thus prevent stale unit test
+		results (waf_unit_test.py).
+
+		Hashing input file timestamps is another possibility for the implementation.
+		This may cause unnecessary rebuilds when input tasks are frequently executed.
+		Here is an implementation example::
+
+			lst = []
+			for node in self.inputs + self.dep_nodes:
+				st = os.stat(node.abspath())
+				lst.append(st.st_mtime)
+				lst.append(st.st_size)
+			self.m.update(Utils.h_list(lst))
+
+		The downside of the implementation is that it absolutely requires all build directory
+		files to be declared within the current build.
+		"""
+		bld = self.generator.bld
+		lst = [bld.task_sigs[bld.node_sigs[node]] for node in (self.inputs + self.dep_nodes) if node.is_bld()]
+		self.m.update(Utils.h_list(lst))
+
+	def sig_vars(self):
+		"""
+		Used by :py:meth:`waflib.Task.Task.signature`; it hashes :py:attr:`waflib.Task.Task.env` variables/values
+		When overriding this method, and if scriptlet expressions are used, make sure to follow
+		the code in :py:meth:`waflib.Task.Task.compile_sig_vars` to enable dependencies on scriptlet results.
+		"""
+		sig = self.generator.bld.hash_env_vars(self.env, self.vars)
+		self.m.update(sig)
+
+	scan = None
+	"""
+	This method, when provided, returns a tuple containing:
+
+	* a list of nodes corresponding to real files
+	* a list of names for files not found in path_lst
+
+	For example::
+
+		from waflib.Task import Task
+		class mytask(Task):
+			def scan(self, node):
+				return ([], [])
+
+	The first and second lists in the tuple are stored in :py:attr:`waflib.Build.BuildContext.node_deps` and
+	:py:attr:`waflib.Build.BuildContext.raw_deps` respectively.
+	"""
+
+	def sig_implicit_deps(self):
+		"""
+		Used by :py:meth:`waflib.Task.Task.signature`; it hashes node signatures
+		obtained by scanning for dependencies (:py:meth:`waflib.Task.Task.scan`).
+
+		The exception :py:class:`waflib.Errors.TaskRescan` is thrown
+		when a file has changed. In this case, the method :py:meth:`waflib.Task.Task.signature` is called
+		once again, and return here to call :py:meth:`waflib.Task.Task.scan` and searching for dependencies.
+		"""
+		bld = self.generator.bld
+
+		# get the task signatures from previous runs
+		key = self.uid()
+		prev = bld.imp_sigs.get(key, [])
+
+		# for issue #379
+		if prev:
+			try:
+				if prev == self.compute_sig_implicit_deps():
+					return prev
+			except Errors.TaskNotReady:
+				raise
+			except EnvironmentError:
+				# when a file was renamed, remove the stale nodes (headers in folders without source files)
+				# this will break the order calculation for headers created during the build in the source directory (should be uncommon)
+				# the behaviour will differ when top != out
+				for x in bld.node_deps.get(self.uid(), []):
+					if not x.is_bld() and not x.exists():
+						try:
+							del x.parent.children[x.name]
+						except KeyError:
+							pass
+			del bld.imp_sigs[key]
+			raise Errors.TaskRescan('rescan')
+
+		# no previous run or the signature of the dependencies has changed, rescan the dependencies
+		(bld.node_deps[key], bld.raw_deps[key]) = self.scan()
+		if Logs.verbose:
+			Logs.debug('deps: scanner for %s: %r; unresolved: %r', self, bld.node_deps[key], bld.raw_deps[key])
+
+		# recompute the signature and return it
+		try:
+			bld.imp_sigs[key] = self.compute_sig_implicit_deps()
+		except EnvironmentError:
+			for k in bld.node_deps.get(self.uid(), []):
+				if not k.exists():
+					Logs.warn('Dependency %r for %r is missing: check the task declaration and the build order!', k, self)
+			raise
+
+	def compute_sig_implicit_deps(self):
+		"""
+		Used by :py:meth:`waflib.Task.Task.sig_implicit_deps` for computing the actual hash of the
+		:py:class:`waflib.Node.Node` returned by the scanner.
+
+		:return: a hash value for the implicit dependencies
+		:rtype: string or bytes
+		"""
+		upd = self.m.update
+		self.are_implicit_nodes_ready()
+
+		# scanner returns a node that does not have a signature
+		# just *ignore* the error and let them figure out from the compiler output
+		# waf -k behaviour
+		for k in self.generator.bld.node_deps.get(self.uid(), []):
+			upd(k.get_bld_sig())
+		return self.m.digest()
+
+	def are_implicit_nodes_ready(self):
+		"""
+		For each node returned by the scanner, see if there is a task that creates it,
+		and infer the build order
+
+		This has a low performance impact on null builds (1.86s->1.66s) thanks to caching (28s->1.86s)
+		"""
+		bld = self.generator.bld
+		try:
+			cache = bld.dct_implicit_nodes
+		except AttributeError:
+			bld.dct_implicit_nodes = cache = {}
+
+		# one cache per build group
+		try:
+			dct = cache[bld.current_group]
+		except KeyError:
+			dct = cache[bld.current_group] = {}
+			for tsk in bld.cur_tasks:
+				for x in tsk.outputs:
+					dct[x] = tsk
+
+		modified = False
+		for x in bld.node_deps.get(self.uid(), []):
+			if x in dct:
+				self.run_after.add(dct[x])
+				modified = True
+
+		if modified:
+			for tsk in self.run_after:
+				if not tsk.hasrun:
+					#print "task is not ready..."
+					raise Errors.TaskNotReady('not ready')
+if sys.hexversion > 0x3000000:
+	def uid(self):
+		try:
+			return self.uid_
+		except AttributeError:
+			m = Utils.md5(self.__class__.__name__.encode('latin-1', 'xmlcharrefreplace'))
+			up = m.update
+			for x in self.inputs + self.outputs:
+				up(x.abspath().encode('latin-1', 'xmlcharrefreplace'))
+			self.uid_ = m.digest()
+			return self.uid_
+	uid.__doc__ = Task.uid.__doc__
+	Task.uid = uid
+
+def is_before(t1, t2):
+	"""
+	Returns a non-zero value if task t1 is to be executed before task t2::
+
+		t1.ext_out = '.h'
+		t2.ext_in = '.h'
+		t2.after = ['t1']
+		t1.before = ['t2']
+		waflib.Task.is_before(t1, t2) # True
+
+	:param t1: Task object
+	:type t1: :py:class:`waflib.Task.Task`
+	:param t2: Task object
+	:type t2: :py:class:`waflib.Task.Task`
+	"""
+	to_list = Utils.to_list
+	for k in to_list(t2.ext_in):
+		if k in to_list(t1.ext_out):
+			return 1
+
+	if t1.__class__.__name__ in to_list(t2.after):
+		return 1
+
+	if t2.__class__.__name__ in to_list(t1.before):
+		return 1
+
+	return 0
+
+def set_file_constraints(tasks):
+	"""
+	Updates the ``run_after`` attribute of all tasks based on the task inputs and outputs
+
+	:param tasks: tasks
+	:type tasks: list of :py:class:`waflib.Task.Task`
+	"""
+	ins = Utils.defaultdict(set)
+	outs = Utils.defaultdict(set)
+	for x in tasks:
+		for a in x.inputs:
+			ins[a].add(x)
+		for a in x.dep_nodes:
+			ins[a].add(x)
+		for a in x.outputs:
+			outs[a].add(x)
+
+	links = set(ins.keys()).intersection(outs.keys())
+	for k in links:
+		for a in ins[k]:
+			a.run_after.update(outs[k])
+
+
+class TaskGroup(object):
+	"""
+	Wrap nxm task order constraints into a single object
+	to prevent the creation of large list/set objects
+
+	This is an optimization
+	"""
+	def __init__(self, prev, next):
+		self.prev = prev
+		self.next = next
+		self.done = False
+
+	def get_hasrun(self):
+		for k in self.prev:
+			if not k.hasrun:
+				return NOT_RUN
+		return SUCCESS
+
+	hasrun = property(get_hasrun, None)
+
+def set_precedence_constraints(tasks):
+	"""
+	Updates the ``run_after`` attribute of all tasks based on the after/before/ext_out/ext_in attributes
+
+	:param tasks: tasks
+	:type tasks: list of :py:class:`waflib.Task.Task`
+	"""
+	cstr_groups = Utils.defaultdict(list)
+	for x in tasks:
+		h = x.hash_constraints()
+		cstr_groups[h].append(x)
+
+	keys = list(cstr_groups.keys())
+	maxi = len(keys)
+
+	# this list should be short
+	for i in range(maxi):
+		t1 = cstr_groups[keys[i]][0]
+		for j in range(i + 1, maxi):
+			t2 = cstr_groups[keys[j]][0]
+
+			# add the constraints based on the comparisons
+			if is_before(t1, t2):
+				a = i
+				b = j
+			elif is_before(t2, t1):
+				a = j
+				b = i
+			else:
+				continue
+
+			a = cstr_groups[keys[a]]
+			b = cstr_groups[keys[b]]
+
+			if len(a) < 2 or len(b) < 2:
+				for x in b:
+					x.run_after.update(a)
+			else:
+				group = TaskGroup(set(a), set(b))
+				for x in b:
+					x.run_after.add(group)
+
+def funex(c):
+	"""
+	Compiles a scriptlet expression into a Python function
+
+	:param c: function to compile
+	:type c: string
+	:return: the function 'f' declared in the input string
+	:rtype: function
+	"""
+	dc = {}
+	exec(c, dc)
+	return dc['f']
+
+re_cond = re.compile('(?P<var>\w+)|(?P<or>\|)|(?P<and>&)')
+re_novar = re.compile(r'^(SRC|TGT)\W+.*?$')
+reg_act = re.compile(r'(?P<backslash>\\)|(?P<dollar>\$\$)|(?P<subst>\$\{(?P<var>\w+)(?P<code>.*?)\})', re.M)
+def compile_fun_shell(line):
+	"""
+	Creates a compiled function to execute a process through a sub-shell
+	"""
+	extr = []
+	def repl(match):
+		g = match.group
+		if g('dollar'):
+			return "$"
+		elif g('backslash'):
+			return '\\\\'
+		elif g('subst'):
+			extr.append((g('var'), g('code')))
+			return "%s"
+		return None
+	line = reg_act.sub(repl, line) or line
+	dvars = []
+	def add_dvar(x):
+		if x not in dvars:
+			dvars.append(x)
+
+	def replc(m):
+		# performs substitutions and populates dvars
+		if m.group('and'):
+			return ' and '
+		elif m.group('or'):
+			return ' or '
+		else:
+			x = m.group('var')
+			add_dvar(x)
+			return 'env[%r]' % x
+
+	parm = []
+	app = parm.append
+	for (var, meth) in extr:
+		if var == 'SRC':
+			if meth:
+				app('tsk.inputs%s' % meth)
+			else:
+				app('" ".join([a.path_from(cwdx) for a in tsk.inputs])')
+		elif var == 'TGT':
+			if meth:
+				app('tsk.outputs%s' % meth)
+			else:
+				app('" ".join([a.path_from(cwdx) for a in tsk.outputs])')
+		elif meth:
+			if meth.startswith(':'):
+				add_dvar(var)
+				m = meth[1:]
+				if m == 'SRC':
+					m = '[a.path_from(cwdx) for a in tsk.inputs]'
+				elif m == 'TGT':
+					m = '[a.path_from(cwdx) for a in tsk.outputs]'
+				elif re_novar.match(m):
+					m = '[tsk.inputs%s]' % m[3:]
+				elif re_novar.match(m):
+					m = '[tsk.outputs%s]' % m[3:]
+				else:
+					add_dvar(m)
+					if m[:3] not in ('tsk', 'gen', 'bld'):
+						m = '%r' % m
+				app('" ".join(tsk.colon(%r, %s))' % (var, m))
+			elif meth.startswith('?'):
+				# In A?B|C output env.A if one of env.B or env.C is non-empty
+				expr = re_cond.sub(replc, meth[1:])
+				app('p(%r) if (%s) else ""' % (var, expr))
+			else:
+				call = '%s%s' % (var, meth)
+				add_dvar(call)
+				app(call)
+		else:
+			add_dvar(var)
+			app("p('%s')" % var)
+	if parm:
+		parm = "%% (%s) " % (',\n\t\t'.join(parm))
+	else:
+		parm = ''
+
+	c = COMPILE_TEMPLATE_SHELL % (line, parm)
+	Logs.debug('action: %s', c.strip().splitlines())
+	return (funex(c), dvars)
+
+reg_act_noshell = re.compile(r"(?P<space>\s+)|(?P<subst>\$\{(?P<var>\w+)(?P<code>.*?)\})|(?P<text>([^$ \t\n\r\f\v]|\$\$)+)", re.M)
+def compile_fun_noshell(line):
+	"""
+	Creates a compiled function to execute a process without a sub-shell
+	"""
+	buf = []
+	dvars = []
+	merge = False
+	app = buf.append
+
+	def add_dvar(x):
+		if x not in dvars:
+			dvars.append(x)
+
+	def replc(m):
+		# performs substitutions and populates dvars
+		if m.group('and'):
+			return ' and '
+		elif m.group('or'):
+			return ' or '
+		else:
+			x = m.group('var')
+			add_dvar(x)
+			return 'env[%r]' % x
+
+	for m in reg_act_noshell.finditer(line):
+		if m.group('space'):
+			merge = False
+			continue
+		elif m.group('text'):
+			app('[%r]' % m.group('text').replace('$$', '$'))
+		elif m.group('subst'):
+			var = m.group('var')
+			code = m.group('code')
+			if var == 'SRC':
+				if code:
+					app('[tsk.inputs%s]' % code)
+				else:
+					app('[a.path_from(cwdx) for a in tsk.inputs]')
+			elif var == 'TGT':
+				if code:
+					app('[tsk.outputs%s]' % code)
+				else:
+					app('[a.path_from(cwdx) for a in tsk.outputs]')
+			elif code:
+				if code.startswith(':'):
+					# a composed variable ${FOO:OUT}
+					add_dvar(var)
+					m = code[1:]
+					if m == 'SRC':
+						m = '[a.path_from(cwdx) for a in tsk.inputs]'
+					elif m == 'TGT':
+						m = '[a.path_from(cwdx) for a in tsk.outputs]'
+					elif re_novar.match(m):
+						m = '[tsk.inputs%s]' % m[3:]
+					elif re_novar.match(m):
+						m = '[tsk.outputs%s]' % m[3:]
+					else:
+						add_dvar(m)
+						if m[:3] not in ('tsk', 'gen', 'bld'):
+							m = '%r' % m
+					app('tsk.colon(%r, %s)' % (var, m))
+				elif code.startswith('?'):
+					# In A?B|C output env.A if one of env.B or env.C is non-empty
+					expr = re_cond.sub(replc, code[1:])
+					app('to_list(env[%r] if (%s) else [])' % (var, expr))
+				else:
+					# plain code such as ${tsk.inputs[0].abspath()}
+					call = '%s%s' % (var, code)
+					add_dvar(call)
+					app('gen.to_list(%s)' % call)
+			else:
+				# a plain variable such as # a plain variable like ${AR}
+				app('to_list(env[%r])' % var)
+				add_dvar(var)
+		if merge:
+			tmp = 'merge(%s, %s)' % (buf[-2], buf[-1])
+			del buf[-1]
+			buf[-1] = tmp
+		merge = True # next turn
+
+	buf = ['lst.extend(%s)' % x for x in buf]
+	fun = COMPILE_TEMPLATE_NOSHELL % "\n\t".join(buf)
+	Logs.debug('action: %s', fun.strip().splitlines())
+	return (funex(fun), dvars)
+
+def compile_fun(line, shell=False):
+	"""
+	Parses a string expression such as '${CC} ${SRC} -o ${TGT}' and returns a pair containing:
+
+	* The function created (compiled) for use as :py:meth:`waflib.Task.Task.run`
+	* The list of variables that must cause rebuilds when *env* data is modified
+
+	for example::
+
+		from waflib.Task import compile_fun
+		compile_fun('cxx', '${CXX} -o ${TGT[0]} ${SRC} -I ${SRC[0].parent.bldpath()}')
+
+		def build(bld):
+			bld(source='wscript', rule='echo "foo\\${SRC[0].name}\\bar"')
+
+	The env variables (CXX, ..) on the task must not hold dicts so as to preserve a consistent order.
+	The reserved keywords ``TGT`` and ``SRC`` represent the task input and output nodes
+
+	"""
+	if isinstance(line, str):
+		if line.find('<') > 0 or line.find('>') > 0 or line.find('&&') > 0:
+			shell = True
+	else:
+		dvars_lst = []
+		funs_lst = []
+		for x in line:
+			if isinstance(x, str):
+				fun, dvars = compile_fun(x, shell)
+				dvars_lst += dvars
+				funs_lst.append(fun)
+			else:
+				# assume a function to let through
+				funs_lst.append(x)
+		def composed_fun(task):
+			for x in funs_lst:
+				ret = x(task)
+				if ret:
+					return ret
+			return None
+		return composed_fun, dvars_lst
+	if shell:
+		return compile_fun_shell(line)
+	else:
+		return compile_fun_noshell(line)
+
+def compile_sig_vars(vars):
+	"""
+	This method produces a sig_vars method suitable for subclasses that provide
+	scriptlet code in their run_str code.
+	If no such method can be created, this method returns None.
+
+	The purpose of the sig_vars method returned is to ensures
+	that rebuilds occur whenever the contents of the expression changes.
+	This is the case B below::
+
+		import time
+		# case A: regular variables
+		tg = bld(rule='echo ${FOO}')
+		tg.env.FOO = '%s' % time.time()
+		# case B
+		bld(rule='echo ${gen.foo}', foo='%s' % time.time())
+
+	:param vars: env variables such as CXXFLAGS or gen.foo
+	:type vars: list of string
+	:return: A sig_vars method relevant for dependencies if adequate, else None
+	:rtype: A function, or None in most cases
+	"""
+	buf = []
+	for x in sorted(vars):
+		if x[:3] in ('tsk', 'gen', 'bld'):
+			buf.append('buf.append(%s)' % x)
+	if buf:
+		return funex(COMPILE_TEMPLATE_SIG_VARS % '\n\t'.join(buf))
+	return None
+
+def task_factory(name, func=None, vars=None, color='GREEN', ext_in=[], ext_out=[], before=[], after=[], shell=False, scan=None):
+	"""
+	Returns a new task subclass with the function ``run`` compiled from the line given.
+
+	:param func: method run
+	:type func: string or function
+	:param vars: list of variables to hash
+	:type vars: list of string
+	:param color: color to use
+	:type color: string
+	:param shell: when *func* is a string, enable/disable the use of the shell
+	:type shell: bool
+	:param scan: method scan
+	:type scan: function
+	:rtype: :py:class:`waflib.Task.Task`
+	"""
+
+	params = {
+		'vars': vars or [], # function arguments are static, and this one may be modified by the class
+		'color': color,
+		'name': name,
+		'shell': shell,
+		'scan': scan,
+	}
+
+	if isinstance(func, str) or isinstance(func, tuple):
+		params['run_str'] = func
+	else:
+		params['run'] = func
+
+	cls = type(Task)(name, (Task,), params)
+	classes[name] = cls
+
+	if ext_in:
+		cls.ext_in = Utils.to_list(ext_in)
+	if ext_out:
+		cls.ext_out = Utils.to_list(ext_out)
+	if before:
+		cls.before = Utils.to_list(before)
+	if after:
+		cls.after = Utils.to_list(after)
+
+	return cls
+
+def deep_inputs(cls):
+	"""
+	Task class decorator to enable rebuilds on input files task signatures
+	"""
+	def sig_explicit_deps(self):
+		Task.sig_explicit_deps(self)
+		Task.sig_deep_inputs(self)
+	cls.sig_explicit_deps = sig_explicit_deps
+	return cls
+
+TaskBase = Task
+"Provided for compatibility reasons, TaskBase should not be used"
+
+class TaskSemaphore(object):
+	"""
+	Task semaphores provide a simple and efficient way of throttling the amount of
+	a particular task to run concurrently. The throttling value is capped
+	by the amount of maximum jobs, so for example, a `TaskSemaphore(10)`
+	has no effect in a `-j2` build.
+
+	Task semaphores are typically specified on the task class level::
+
+		class compile(waflib.Task.Task):
+			semaphore = waflib.Task.TaskSemaphore(2)
+			run_str = 'touch ${TGT}'
+
+	Task semaphores are meant to be used by the build scheduler in the main
+	thread, so there are no guarantees of thread safety.
+	"""
+	def __init__(self, num):
+		"""
+		:param num: maximum value of concurrent tasks
+		:type num: int
+		"""
+		self.num = num
+		self.locking = set()
+		self.waiting = set()
+
+	def is_locked(self):
+		"""Returns True if this semaphore cannot be acquired by more tasks"""
+		return len(self.locking) >= self.num
+
+	def acquire(self, tsk):
+		"""
+		Mark the semaphore as used by the given task (not re-entrant).
+
+		:param tsk: task object
+		:type tsk: :py:class:`waflib.Task.Task`
+		:raises: :py:class:`IndexError` in case the resource is already acquired
+		"""
+		if self.is_locked():
+			raise IndexError('Cannot lock more %r' % self.locking)
+		self.locking.add(tsk)
+
+	def release(self, tsk):
+		"""
+		Mark the semaphore as unused by the given task.
+
+		:param tsk: task object
+		:type tsk: :py:class:`waflib.Task.Task`
+		:raises: :py:class:`KeyError` in case the resource is not acquired by the task
+		"""
+		self.locking.remove(tsk)
+