[Scons-users] Value/Alias Nodes default to up-to-date

Bill Deegan bill at baddogconsulting.com
Sun Jan 2 22:52:47 EST 2022 

Can you give a more concrete example of what you're trying to do?
Sounds like you want a target which isn't built unless explicitly requested?
Is that correct?
An your current approach is to use an Action for that?

Lots of users dig around the docs and come up with some poorly constructed
overcomplicated "solution".
I'm trying to help you avoid doing such.

Yes. If any node has no children or the children are up to date, then it
will not rebuild the node.. (as you'd expect).


On Sun, Jan 2, 2022 at 5:37 PM Brad Kraemer <computerpro_58 at hotmail.com>
wrote:

> Simply that I can use the Node returned by Alias() in places where a Node
> is expected (for instance in the example I've given Depends(t1, a1)).
>
> Now you may ask why wouldn't I use Command(), since that it's defined
> purpose? In this case I wanted the special property of Alias Node's (they
> exist in their own namespace, outside the standard FS namespace). Well why
> would I need this target to exist outside the standard FS namespace? Simply
> because I have some internal Action's that I want to run (in the process of
> building) that are not specific to any target (that the user can specify).
> i.e. $ scons / , or $ scons . is not going to pick up these Alias Node
> targets (and thats exactly what I want).
>
>
> My reasons for wanting this are more abstract at this point (as I said I'm
> experimenting around the limitations of SCons). But to save some time here,
> I'm literally looking for a Yes or No answer, with regards to the
> Alias/Value node's up-to-date behavior.
>
> Specifically, check the file: /SCons/Node/__init__.py:1520
>
>  def children_are_up_to_date(self):
>      """Alternate check for whether the Node is current:  If all of
>      our children were up-to-date, then this Node was up-to-date, too.
>      The SCons.Node.Alias and SCons.Node.Python.Value subclasses
>      rebind their current() method to this method."""
>      # Allow the children to calculate their signatures.
>      self.binfo = self.get_binfo()
>      if self.always_build:
>          return None
>      state = 0
>      for kid in self.children(None):
>          s = kid.get_state()
>          if s and (not state or s > state):
>              state = s
>      return (state == 0 or state == SCons.Node.up_to_date)
>
>
> *Both Value/Alias Node's use this method to cite there up-to-date state.
> As written, with either no children or children with unchanging states a
> Value/Alias will always be considered up-to-date (i.e. it is considered
> built/up-to-date directly after creation). Is this correct?
>
>
> If this behavior is correct what is the purpose of the 'built_value'
> business on Value Node's? I don't fully grasp how Value Node's are meant to
> work in the standard case...
>
>
> On 2022-01-02 8:05 p.m., Bill Deegan wrote:
>
> Still don't really understand what you're trying to do.
>
> What do you mean by this "allowing me to make Action()'s with dependency
> orderings"?
>
> On Sun, Jan 2, 2022 at 3:10 PM Brad Kraemer <computerpro_58 at hotmail.com>
> wrote:
>
>> * Fixed subject line (the original line from the mailer daemon added
>> JUNK, as this one doesn't allow unconfirmed posters, i.e. I should have
>> waited for the mailing-list confirmation before sending the first e-mail
>> off)
>>
>>
>> Currently, just experimenting with some SCons features. At this time I
>> was creating an Alias() because I wanted the Alias() object (which is
>> namespaced outside the regular FS namespace), allowing me to make
>> Action()'s with dependency orderings. While not having these actions kicked
>> off by running something like '$ scons /' (which something like Command()
>> would).
>>
>>
>> I realize this is outside the intended use of these functions. However,
>> the doc's don't forbid it so it's clean in my eyes.
>>
>> The Command() part is just for something to depend on (can replace it
>> with Program() or any other builder, my issue is with the Alias() lines).
>>
>>
>> Your reasoning makes sense, however, if my Alias is never out of date
>> (i.e. on creation it's meant to be considered already built), why can I run
>> AlwaysBuild() and thus force it to build (is this the equivalent of
>> rebuilding something already up-to-date)?
>>
>> Just looking at the sources, it seems these Node's are meant to be built
>> at least once (however, Value() in particular does seem to have a parameter
>> to be considered built on creation). Or am I off base with this?
>>
>>
>> On 2022-01-02 5:30 p.m., Bill Deegan wrote:
>>
>> Maybe you explain what you're trying to do, rather than how you're
>> currently trying to do it?
>> Because this looks like a mess of hard to understand code and there's
>> very likely a better way to do this.
>>
>> Those aliases would never be out of date with a static source.
>> Your command has no source listed, so it will also never be out of
>> date..(after the first time, if the file t1 was actually built).
>>
>> -Bill
>>
>>
>> On Sun, Jan 2, 2022 at 2:20 PM Bill Deegan <bill at baddogconsulting.com>
>> wrote:
>>
>>> also why **JUNK** in subject?
>>>
>>> On Sun, Jan 2, 2022 at 2:20 PM Bill Deegan <bill at baddogconsulting.com>
>>> wrote:
>>>
>>>> What output do you see when you run your example?
>>>>
>>>>
>>>> On Sun, Jan 2, 2022 at 7:56 AM Brad Kraemer <computerpro_58 at hotmail.com>
>>>> wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I filed a GitHub Issue <https://github.com/SCons/scons/issues/4079>
>>>>> and got bounced to this mailing list. So here we go again:
>>>>>
>>>>> Value/Alias nodes (as created by the Alias() and Value()
>>>>> functions/methods receptively) default to up-to-date.
>>>>>
>>>>> SCons 4.1.0
>>>>>
>>>>> Python 3.9
>>>>>
>>>>> Installed from nixpkgs (NixOS, $ nix-env -iA nixos.scons)
>>>>>
>>>>> Linux
>>>>>
>>>>> Reproduction (SConstruct):
>>>>>
>>>>> def print_target_1(target, source, env):
>>>>>    print("Target 1 built")
>>>>>
>>>>> def print_alias_1(target, source, env):
>>>>>    print("[I'm not getting called]")
>>>>>
>>>>> def print_alias_2(target, source, env):
>>>>>    print("I'm getting called because of AlwaysBuild() workaround")
>>>>>
>>>>> t1 = Command("t1", [], Action(print_target_1, cmdstr=None))
>>>>> Default(t1)
>>>>>
>>>>> v = Value("_")
>>>>> a1 = Alias("a1", v, Action(print_alias_1, cmdstr=None))
>>>>> a2 = Alias("a2", v, Action(print_alias_2, cmdstr=None))
>>>>> Depends(t1, a1)
>>>>> Depends(t1, a2)
>>>>>
>>>>> AlwaysBuild(a2)
>>>>>
>>>>>
>>>>> Invoke via executing '$ scons' from the directory where the above
>>>>> SConstruct file exists.
>>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>> simplejack-src
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Scons-users mailing list
>>>>> Scons-users at scons.org
>>>>> https://pairlist4.pair.net/mailman/listinfo/scons-users
>>>>>
>>>>
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