Use output of waf Task in other waf Task

Question

I want to use the target of a waf Task as source in another waf Task, but this does not work as expected.

A simple but complete example: I added two Tasks (t_1, t_2) I want to add as a feature and added their constraints by before and after.

• In Task t_1 I use src=link_task.outputs[0] as src and link_task.outputs[0].change_ext('.txt') as tgt for the Task.

• But in t_2 I want to use the output/target of t_1 as input. I assumed I can get it by referencing self.t_1.ouputs, but this seems to be wrong. Why does this work for in t_1 for the apply_link Task, but not for t_1?

---

1. MWE: wscript

   from waflib import Context, Options
   from waflib import Task, TaskGen
   from waflib.Tools.compiler_c import c_compiler
   
   def options(opt):
           opt.load('compiler_c')
   
   def configure(cnf):
           cnf.load('compiler_c')
   
   def build(bld):
           bld.program(features=['t_1', 't_2'], source='main.c', target="abc")
   
   class t_1(Task.Task):
       always_run = True
       run_str = 'echo ${SRC} && echo hello t_1 > ${TGT}'
       color = 'RED'
   
   
   @TaskGen.feature('t_1')
   @TaskGen.after('apply_link')
   @TaskGen.before('t_2')
   def add_t_1_task(self):
       try:
           link_task = self.link_task
       except AttributeError as err:
           print err
           return
       self.create_task('t_1', src=link_task.outputs[0], tgt=link_task.outputs[0].change_ext('.txt'))
   
   
   class t_2(Task.Task):
       always_run = True
       run_str = 'echo ${SRC}'
       color = 'RED'
   
   
   @TaskGen.feature('t_2')
   @TaskGen.after('apply_link', 't_1')
   def add_t_2_task(self):
       try:
           t_1 = self.t_1
       except AttributeError as err:
           print err
           return
       self.create_task('t_2', src=t_1.outputs[0])
   

---

2. Running python waf configure build leads to:

   user@laptop /cygdrive/c/work
   $ python waf-1.9.13 configure clean build
   Setting top to                           : /cygdrive/c/work
   Setting out to                           : /cygdrive/c/work/build
   Checking for 'gcc' (C compiler)          : /usr/bin/gcc
   'configure' finished successfully (0.150s)
   'clean' finished successfully (0.010s)
   Waf: Entering directory `/cygdrive/c/work/build'
   'task_gen' object has no attribute 't_1' <===================== How to get this working
   [1/3] Compiling main.c
   [2/3] Linking build/abc.exe
   [3/3] Compiling build/abc.exe
   abc.exe
   
   Waf: Leaving directory `/cygdrive/c/work/build'
   'build' finished successfully (0.270s)
   

Answer 1

The before and after decorators apply to task generator methods, not tasks. You should have:

@TaskGen.feature('t_1')
@TaskGen.after('apply_link')
# correction: no need to use @TaskGen.before('add_t_2_task')
def add_t_1_task(self):

    # correction: you have to define self.t_1

    self.t_1 = self.create_task(
        't_1',
        self.link_task.outputs[0], 
        self.link_task.outputs[0].change_ext('.txt')
    )

@TaskGen.feature('t_2')
@TaskGen.after('apply_link', 'add_t_1_task') # correction: use method name
def add_t_2_task(self):

    # add_t-2_task is executed after add_t_1_task, so using self.t_1 is ok

    print "t_1", self.t_1

By the way, do not use always_run=True as it defeats one of waf main feature, ie only build what you need to build :)