[Scons-users] Retrieving variables

[Bill Deegan]

Stefan,



On Fri, Jun 17, 2016 at 6:35 AM, Stefan Seefeld <stefan at seefeld.name> wrote:

> Hi Bill,
>
> sorry for a belated followup.
>
> On 14.06.2016 15:47, Bill Deegan wrote:
>
> >
> >     While this may work, it really looks like a kludge.
> >
> >
> > not sure what you are referring to here..
>
> Explicitly instantiating a tool seems to imply that I want to override
> the automatic choice, so the semantic is (at least slightly) changed.


Not exactly.  It means you want to be explicit about loading tools.
You may not want to load all the available ones, it is also an optimization
as loading all tools can slowsdown scons startup.
So in the case where you only need tools x,y, and z, you can specify only
those.
In your case you want to defer loading msvc until you are able to set some
variables to aid in its configuration.
This is not an odd or unusual event to do any of the above.



> So
> I at least need some extra logic to check whether msvc is present at all
> on my machine. If I run `env.Tool('msvc')` unconditionally on Linux, I get
>
>   scons: warning: No version of Visual Studio compiler found - C/C++
> compilers most likely not set correctly
>
> while what I really want is to delay SCons' own (conditional)
> initialization of the 'msvc' tool until the TARGET_ARCH variable is
> correctly set.
>



>
> But experimenting with this, I ran into other issues, as well:
>
> >
> > env=Environment(tools=[], variables=vars)
> >
> > env['TARGET_ARCH'] = env['arch']
> > env.Tool('msvc')
> >
> > Should more or less do what you want.
>
> Here is my current logic:
>
>   env = Environment(toolpath=['config'],
>                     tools=['default', 'build_variants', 'boost_libs',
> 'boost_tests'],
>                     variables=vars)
>   env['TARGET_ARCH'] = env['arch']
>   env.Tool('msvc')
>
> which yields:
>
>   EnvironmentError: No module named msvc:
>
> Any idea why ? (Is SCons by any chance looking for tools *only* in
> config/ ?) But it gets slightly worse: My `config/` directory actually
> contains a 'msvc.py' module. And with that, I get a different error:
>

>   AttributeError: 'module' object has no attribute 'generate':
>
> because that module isn't a 'tool' at all (and as it isn't listed in the
> 'tools' constructor argument above, I had assumed it would not be read).
> So, I don't understand the precise semantics of the 'toolpath' and
> 'tools' constructor arguments. (I thought the 'default' value was
> supposed to tell SCons to load all the built-in tools first, and only
> add the other ones mentioned above from the provided toolpath.
> Please clarify the documentation.
>

The documentation is fairly clear on this (from manpage).  Sounds like you
are telling SCons you have tools in config, then you have a file named
msvc.py which scons trys to load as the msvc tool which doesn't specify the
required methods and so scons fails loading the tool. This is pretty much
what the doc snippet below says. See bit highlighed in red.

Non-built-in tools may be specified using the toolpath argument:

env = Environment(tools = ['default', 'foo'], toolpath = ['tools'])

This looks for a tool specification in tools/foo.py (as well as using the
ordinary default tools for the platform). foo.py should have two functions:
generate(env, **kw) and exists(env). Thegenerate() function modifies the
passed-in environment to set up variables so that the tool can be executed;
it may use any keyword arguments that the user supplies (see below) to vary
its initialization. The exists() function should return a true value if the
tool is available. Tools in the toolpath are used before any of the
built-in ones. For example, adding gcc.py to the toolpath would override
the built-in gcc tool. Also note that the toolpath is stored in the
environment for use by later calls to *Clone*() and *Tool*() methods:
If you specify a toolpath, then really no files which are not tools,
especially if they are named the same as existing tools, should be in that
directory.

-Bill




>
> Thanks,
>         Stefan
>
>
> --
>
>       ...ich hab' noch einen Koffer in Berlin...
>
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