[Scons-users] Is it normal that changing a construction environment does not trigger a build

[Bill Deegan]

Per the manpage: (search for varlist= in the manpage)
Use Action()'s varlist argument like this:

# Alternatively, use a keyword argument.
a = Action(build_it, varlist=['DATA'])



On Tue, Oct 9, 2018 at 5:02 AM Arevalo Reggeti, Juan Carlos Ramon (CW) <
exceltic-services.juan.arevalo at hp.com> wrote:

> Hi all,
>
>
>
> I noticed that in SCons the decider is not called on targets with no
> dependencies, which I can understand given that the build should entirely
> depend on the construction env.
>
> However, I noticed that if you changed the environment on a target with no
> dependencies the build is not triggered, but it is when the builder is
> changed.
>
>
>
> I put together an example below (and attached the files) where every time
> the SConstruct file is read the environment changes, but the target gets
> built only once.
>
>
>
> My questions are: Shouldn’t a change in the environment  trigger a new
> build? If not, is there a workaround other than including a dummy target to
> make a custom decider that compares environments?
>
>
>
> For example take this simple SConstruct:
>
>
>
> ******************* SCONSTRUCT**************
>
> #!python
>
>
>
> import random
>
>
>
> print ("-----------NEW EXECUTION-----------")
>
> env = Environment(DATA =  str(random.randint(0,20)) + "\n")
>
>
>
> def generate_dummy_file(target, env):
>
>     with open(str(target), 'w') as f:
>
>         f.write(env["DATA"])
>
>
>
> def my_builder(target, source, env):
>
>     generate_dummy_file(target[0], env)
>
>
>
> env.Append(BUILDERS = {'MyBuilder' : Builder(action=my_builder)})
>
>
>
>
>
>
>
> print ("Environment data: " + env["DATA"])
>
> print ("")
>
> target = env.MyBuilder('dummy_file.txt',[])
>
>
>
> *************** EXECUTION LOG *******************
>
>
>
> [arevalor at vl337 example]$ for INDEX in {1..2}; do scons; done
>
> scons: Reading SConscript files ...
>
> -----------NEW EXECUTION-----------
>
> Environment data: 13
>
>
>
>
>
> scons: done reading SConscript files.
>
> scons: Building targets ...
>
> my_builder(["dummy_file.txt"], [])
>
> scons: done building targets.
>
> scons: Reading SConscript files ...
>
> -----------NEW EXECUTION-----------
>
> Environment data: 7
>
>
>
>
>
> scons: done reading SConscript files.
>
> scons: Building targets ...
>
> scons: `.' is up to date.
>
> scons: done building targets.
>
>
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>
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