[Scons-users] Ignore and Requires

[William Blevins]

So I just checked the documentation.  Gary is right like always ;)

Even more curiously, do you even need to do the Ignore before a Requires
(assuming Ignores + Requires works as desired)?

Seriously though, is there a "Requires" that causes the item to be a
"normal" node?

V/R,
William

On Wed, Oct 15, 2014 at 8:49 PM, William Blevins <wblevins001 at gmail.com>
wrote:

> Requires() re-adds it, but in the special
>> Requires way, so the file has to exist but changes to it don't trigger
>> a rebuild.
>
>
> Then what is the way to "Require" and rebuild if it changes?  I hope
> require does check.  If it doesn't, then the dependency tree is essentially
> neutered.
>
> V/R,
> William
>
> On Wed, Oct 15, 2014 at 8:44 PM, Gary Oberbrunner <garyo at oberbrunner.com>
> wrote:
>
>> Actually, I think it might work, if I understand what you're doing.
>> The revision.cpp file starts as a dependency of the target.  Ignore()
>> removes that dependency.  Requires() re-adds it, but in the special
>> Requires way, so the file has to exist but changes to it don't trigger
>> a rebuild.  I'm not positive about this, haven't tried it myself.
>>
>> Arvid, the ugly workaround you mention is the accepted method for
>> this, because it prevents the revision.cpp file from being in the
>> dependency tree in the first place.  But your idea to use Ignore is
>> clever; if it does actually work, let's put a testcase into SCons so
>> we can make sure it keeps working.
>>
>> -- Gary
>>
>> On Wed, Oct 15, 2014 at 8:31 PM, William Blevins <wblevins001 at gmail.com>
>> wrote:
>> > Arvid,
>> >
>> > I'm not sure you can achieve this the way you desire.  Your approach
>> > fundamentally contradicts the results.  Using Requires makes the
>> generated
>> > CPP-file an explicit dependency.  You are manually injecting the new
>> > CPP-file into the dependency graph.  Since the file new has a different
>> > name, methods like checking the md5sum cannot detect the lack of
>> changes;
>> > thus, the library will always be linked.
>> >
>> > Is this a situation where you can use a soft-link to trick SCons into
>> > keeping a consistent file name?
>> >
>> > V/R,
>> > William
>> >
>> > On Wed, Oct 15, 2014 at 5:38 PM, Arvid Rosén <arvid at softube.com> wrote:
>> >>
>> >> Hi!
>> >>
>> >> I generate a .cpp file with a revision number. It is compiled and
>> linked
>> >> with a lot of other object files. However, I don’t want to re-link if
>> only
>> >> the revision number has changed.
>> >>
>> >> I thought order-only dependencies using ”Requires” function would solve
>> >> this, but if I state that the final binary ”Requires” the
>> revision-object,
>> >> the binary is still always re-linked. I guess this is because the
>> revision
>> >> object file is in the source list of the link command, so it gets
>> added as
>> >> an implicit dependency. There is a ugly workaround (passing the
>> revision
>> >> object as a link flag) in the user guide:
>> >> http://www.scons.org/doc/2.3.1/HTML/scons-user.html#idp2498640
>> >>
>> >> But, can I achieve the same thing by using the Ignore function
>> followed by
>> >> Requires? It seems to work, but I don’t know if I am guarantied that
>> the
>> >> files are built in the right order.
>> >>
>> >> Cheers,
>> >> Arvid
>> >> _______________________________________________
>> >> Scons-users mailing list
>> >> Scons-users at scons.org
>> >> https://pairlist4.pair.net/mailman/listinfo/scons-users
>> >
>> >
>> >
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>> >
>>
>>
>>
>> --
>> Gary
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>>
>
>
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