[Scons-users] Tool specification `exists()` not called?

[Marc Joliet]

Am Wed, 09 Oct 2013 22:09:24 +0200
schrieb Dirk Bächle <tshortik at gmx.de>:


> On 09.10.2013 21:05, Márcio Faustino wrote:

> > Hi Dirk,

> >

> > I read it online at 

> > <http://www.scons.org/doc/production/HTML/scons-man.html#lbAG>, in the 

> > paragraph starting with "This looks for a tool specification in".

> >

> 

> Although this paragraph doesn't state explicitly that the exists() 

> method gets called (nit-picking, I know ;) ), I can understand how it 

> may be misleading...


I had the same confusion, so perhaps that part of the documentation should be
rephrased sometime.


> > If user defined tools won't have their "exists()" called, what is the 

> > appropriate thing to do in order to signal that a tool does not exist?

> >

> 

> There is no easy answer to this question, I'm afraid. Note that a revamp 

> of the current SCons toolchain handling is on our Roadmap ( 

> http://www.scons.org/wiki/Roadmap ) for the near future.


Yay!


> My current personal view on this is: A Tool itself is always present, 

> otherwise you'd get an ImportError. Tools that don't define any 

> Builders, but simply change the Environment, should always return True. 

> A Tool should return False or '' from its exists() method, if the user 

> has no chance to get its defined Builders working by setting internal 

> variables, especially $PATH.

> As a user I still want to be able to say:

> 

>    env = Environment(tools=[])

>    # Builders get installed, even though the executables are

>    # not found on the path

>    env.Tool('Qt4')

>    # Now we correct the paths to our commands

>    # and make the Builders work

>    env['QT4DIR'] = '/something/special/not/in/path'


I prefer to expose (and, as a user, have exposed) that sort of potentially
system-dependent variable as a construction variable (so that I can call "scons
QT4DIR=/some/path") and have the tool test for that and return False if it, for
example, still can't find a required program.

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup
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