Add EnvContext to simplify configuration-dependent command definition

ChangeLog

@@ -10,26 +10,30 @@ NEW IN WAF 1.9
   - Merge ${FOO}${BAR} flags in commands executed without a shell (no space added)
   - Interpret empty command-line defines as integer values #1704
   - Waf tools are not cached on "waf configure" by default anymore; pass conf.load(.., cache=True)
+  - Enable a consistent progress bar output #1641
   - New --profile command-line option
+  - Add ${VAR?X} constructs in script expressions to enable simple conditional outputs
+  - Enable 'waf dist' to package arbitrary symlinks in tarballs #1719
 
 * Performance highlights:
   - Reduce the key size in bld.task_sigs by adding bld.node_sigs and bld.imp_sigs
   - Remove __hash__ and __eq__ from Context, Node and Task #1629
   - Make lazy visual studio detection the default
-  - Remove the uses of run_once that creates unfree-able memory
-  - Enable a consistent progress bar output #1641
-  - Reduce the memory footprint of Task objects, up to 50% memory reduction on large builds
-  - Enabled pre-forked builds by default to achieve faster builds, up to 2x speedup on short-lived processes
+  - Remove the uses of run_once that can consume a lot of memory
+  - Enable pre-forked builds by default to achieve faster builds, up to 2x speedup on short-lived processes
 
 * API changes:
   - The minimum Python version required is Python 2.5
-  - Remove the duplicate split functions from Utils
+  - Remove the duplicate split() functions from Utils
   - Remove the command called "update"
   - Add Task.get_cwd()
   - Remove Utils.nogc
   - Modify Utils.run_once so that it accepts a list of *args
-  - Improve the task consumer in Runner.py
+  - Rewrote the main task consumer in Runner.py for performance purposes
   - Use relative paths in apply_incpaths by default (and absolute ones when paths cross drives)
   - Remove Configure.err_handler
-  - Remove TaskBase.attr() as it was never used
+  - Remove TaskBase.attr() which was never used
   - Task.sig_vars, Task.sig_explit_deps and Task.sig_implicit_deps return None
+  - Better consistency between check_cfg and check_cc variables
+  - Subclass waflib.Build.ConfiguredContext to enable configuration-dependent user commands
+

TODO

@@ -1,8 +1,6 @@
 Waf 1.9
 -------
 
-* Better consistency between check_cfg and check_cc variables
-* Let more context commands depend on the configuration
 * Rework qt5
 * Regexps for extension-based processing
 * Other issues listed on https://github.com/waf-project/waf/issues

docs/book/examples/configuration_contexts/wscript

@@ -0,0 +1,18 @@
+#! /usr/bin/env python
+# encoding: utf-8
+
+"""
+Call 'waf configure display'
+"""
+
+def configure(conf):
+	pass
+
+from waflib.Build import EnvContext
+class fu_class(EnvContext):
+	cmd = 'display'
+
+def display(self):
+	print(self.env.PREFIX)
+
+

waflib/Build.py

@@ -1348,3 +1348,12 @@ class StepContext(BuildContext):
 				return pattern.match(node.abspath())
 		return match
 
+class EnvContext(BuildContext):
+	"""Subclass EnvContext to create commands that require configuration data in 'env'"""
+	fun = cmd = None
+	def execute(self):
+		self.restore()
+		if not self.all_envs:
+			self.load_envs()
+		self.recurse([self.run_dir])
+