[Scons-users] Dependency between Command calls

[Bill Deegan]

This should be pretty close to what you want:

https://gist.github.com/bdbaddog/698e0c4fe9922eb24da6a66cd760f8a1

Give it a try and let us know what you think.
Also it may be easier to get your solution working if you join our discord
server.
https://discord.gg/bXVpWAy

-Bill
SCons Project Manager

On Sat, Apr 12, 2025 at 12:26 PM Mats Wichmann <mats at wichmann.us> wrote:

> On 4/12/25 12:13, Oliver Koch via Scons-users wrote:
> > Dear SCons experts,
> >
> > Thank your for your last supporting comments!
> >
> > I have developed a small SConstruct file (attached) that implements to
> > tool calls via Command().
> > However, I have a few questions regarding generalization as given in the
> > comments of the SConstruct file.
> >
> > The required input file (MyDeps.puml) is also attached.
> >
> > The output of the two subsequent runs of "scons" are given in Run1.out
> > and Run2.out.
> >
> > So, the build is executed as intended, but the toy example is not really
> > scalable to a real world tool chain.
> >
> > Could you answer my questions resp. give me some hints, how to make this
> > a "real" build chain?
> >
> > Thank you!
> >
> > Oliver
>
> A few comments, out of order.
>
> # This is not executed. Why?
> act = env.Action(PlantUML, cmdstr="Building ${TARGET}")
>
> The Action method produces an action object, but you never do anything
> with that action object. You have to tell something that act is its
> action before anything happens with it. It's fine to pass it to Command,
> that works in the same way as passing it an action string (which will
> anyway be converted to an action object). So like:
>
> tgt = env.Command(target, source, action=act)
>
> ----
>
> from SCons.Script import *
>
> you don't need to do that in an SConstruct/SConscript file, the
> execution context causes it to be done for you.  Where you need that
> import is in files that are run directly and not executed by the
> SConscript() function.
>
> ----
>
> The classic way to scale when there are many files is to write a
> builder.  I think we've previously sent you links on that, please check
> the earlier messages.  But you don't have to. You could also take this:
>
> # I am lloking for something like:
> # for svg in SVGs:
> #   env.Command(svg.basename + '.svgz', svg, SVGZ)
>
> and actually enable it, there's no real reason it wouldn't work
>
> from pathlib import Path
>
> for svg in SVGs:
>      tgtpath = str(Path(svg).name) + '.svgz'
>      env.Command(tgtpath, svg, action=SVGZ)
>
>
> That's a bit "hacky", you should properly let SCons compute the path and
> there are facilities for doing so. If you write a real Builder, part of
> the plumbing it the knowlede of how to transform source to target names
> for the type of files that builder handles.-
>
> There's also a function which can let you find files - read up on Glob
> in the manual. The nice thing about Glob() is it "finds" files that
> haven't been built yet, as it can compute targets based on the
> information in the graph. So you can potentially:
>
> for svg in env.Glob('*.svg'):   # these will be Nodes, unless you add a
> strings=True arg
>
> ----
>
> def PlantUML(target, source, env):
>    import os
>    for src in source:
>      Cmd = 'java.exe' + \
>            ' -jar C:\\Progra~1\\PlantUML\\plantuml.jar' + \
>            ' -tsvg ' + str(src)
>      print('Calling: ', Cmd)
>      os.system(Cmd)
>    # target should not be an input, but is given from Cmd output.
>    # How to make a list of targets from the just created files?
>    for tgt in target:
>      print('  Creating: ', str(tgt))
>
> If you do things this way, you bypass the work SCons does for you. If
> you build a command string like Cmd, and include substitutable elements
> (like $SOURCE), and pass that to Command (instead of going directly out
> via os.system() - and fwiw, using subprocess.run() is preferred if you
> *MUST*), then bingo: the return from Command is the list of targets it
> computed, and you have your answer to
>
>    # How to make a list of targets from the just created files?
>
>
>
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