[Scons-users] Per target env variables

[RW]

Hi Bill,
Thanks for the info

As a seperate question I'm wondering if I should try to add Override() to
the user docs, or if it's classed as a non public API which might change
later on
I dont think it's depreciated looking at the code
it looks like the Builder.py uses it to actually do it's overrides under
the hood
and the Override() call is just a wrapper around the OverrideEnvironment
class

Many Thanks
Richard


On Thu, 6 Sep 2018 at 05:17, Bill Deegan <bill at baddogconsulting.com> wrote:

> If it's not in the users guide or manpage it's not subject to deprecation
> cycle..
> (Those are the definitive spec for the user facing API for SCons.  Thus
> the checklist item on pull requests for docs and tests (and src/CHANGES.txt
> modifications))
>
> Why so many clones? Are the environment's being modified?
> Are you seeing that the # of clones is actually causing you issues?
> Are you Clone'ing as a form of write protection on the original env?
> How many objects does "--debug=count" output for your build?
>
> -Bill
>
>
> On Thu, Sep 6, 2018 at 12:11 AM Jonathon Reinhart <
> jonathon.reinhart at gmail.com> wrote:
>
>> Thanks Bill,
>>
>> You're right, using the CFLAGS="$CFLAGS -Os" substitution is simpler.
>> I sometimes forget how well this works in SCons, and get worried about
>> bash-isms regarding spaces, etc.
>>
>> I could have sworn that env.Override() was in the man page, but it
>> looks like I was wrong.  We've been trying to reduce the number of
>> Clone()s in a large codebase (specifically in some custom
>> pseudo-builders) and I've successfully used env.Override() for this
>> purpose. Given that there are tests for it (in EnvironmentTests.py),
>> it seemed unlikely to go away.
>>
>> Jonathon
>>
>>
>> On Wed, Sep 5, 2018 at 11:57 PM Bill Deegan <bill at baddogconsulting.com>
>> wrote:
>> >
>> > Don't use something which is not in the manpage.
>> > It can be dropped without warning.
>> >
>> > If you're going to use the modified CFLAGS as below many times
>> > Then using Clone() is reasonable.
>> >
>> > So here's what I'd sugguest:
>> > env=Environment(tools=[], MY_FLAG='ABC DEF')
>> > env2=env.Clone(MY_FLAG="$MY_FLAG XYZ PQR")
>> >
>> > print env['MY_FLAG']
>> > print env2['MY_FLAG']
>> >
>> > Here's the output you'd get from such:
>> > scons: Reading SConscript files ...
>> > ABC DEF
>> > ABC DEF XYZ PQR
>> > scons: done reading SConscript files.
>> > scons: Building targets ...
>> > scons: `.' is up to date.
>> > scons: done building targets.
>> >
>> > If you were only doing this for one target then:
>> > env.Program('target',[ sources ], CFLAG="$CFLAG -Os")
>> > (Jonathon Reinhart this is a bit simpler than the method you're
>> recommending)
>> >
>> > Should do the trick.
>> >
>> > Here's the caveat.
>> > Don't make a gazillion Clone's they're not lightweight.
>> > If you make 100, it won't kill you, if you make 1000's you may start
>> seeing memory and speed impacted.
>> >
>> > If you need to modify a flag, only for a single target, or a handful,
>> and especially in your case where you want to programmatically convert a
>> makefile which does such, then regular overrides are fine:
>> > I'm talking about this:
>> > env.Program('target',[ sources ], CFLAG="$CFLAG -Os")
>> >
>> >
>> > BTW if you get anything functional we'd be happy to pull it into:
>> >   https://github.com/SCons/scons-contrib
>> >
>> > -Bill
>> > SCons Project Co-Manager
>> >
>> > On Wed, Sep 5, 2018 at 8:41 PM RW via Scons-users <
>> scons-users at scons.org> wrote:
>> >>
>> >> Thanks for the info
>> >> I was wondering if there might have been a per target / file thing
>> like with Require()
>> >> I think I'll use the Override example you've given above to use an
>> OverrideEnvironment()
>> >> that seems to be the best way
>> >>
>> >> this seems to work
>> >> env2 = env.Override(
>> >>     {'CFLAGS': env.get('CFLAGS', []) + ['-Os']}
>> >> )
>> >>
>> >> I think the Override method isn't documented in the user manual / man
>> page list of functions from the looks of things.
>> >>
>> >> For info I started writing a script to convert Makefiles to scons
>> scripts
>> >> it's still very crude at this stage, and mostly tries to capture
>> variable assignments and if blocks (not so much the rules) just to try and
>> take out the majority of the leg work, still someone might find it usefull
>> >> https://github.com/grbd/Scons.Make2Scons
>> >>
>> >> Many Thanks
>> >> Richard
>> >>
>> >> On Thu, 6 Sep 2018 at 01:09, Jonathon Reinhart <
>> jonathon.reinhart at gmail.com> wrote:
>> >>>
>> >>> Hi Richard,
>> >>>
>> >>> You're correct that this syntax will override the variable (via an
>> >>> OverrideEnvironment), effectively replacing it:
>> >>>
>> >>>     env.Program('hello', 'hello.c', CFLAGS=['-Os'])
>> >>>
>> >>> I wish something like this would exist, but it's not valid Python
>> syntax:
>> >>>
>> >>>     env.Program('hello', 'hello.c', CFLAGS+=['-Os'])
>> >>>
>> >>> The best method I've found is this:
>> >>>
>> >>>     env.Program('hello', 'hello.c',
>> >>>         CFLAGS = env.get('CFLAGS', []) + ['-Os'],
>> >>>     )
>> >>>
>> >>> Alternatively, you can clone the environment to customize it for a set
>> >>> of similar targets:
>> >>>
>> >>>     foo_env = env.Clone()
>> >>>     foo_env.Append(CFLAGS=['-Os'])
>> >>>     foo_env.Program('hello', 'hello.c')
>> >>>
>> >>> Do note that Clone() is expensive, and should be avoided in my
>> >>> opinion. If you're not doing anything too crazy, you can get by with
>> >>> an OverrideEnvironment:
>> >>>
>> >>>     envo = env.Override(
>> >>>         CFLAGS = env.get('CFLAGS', []) + ['-Os'],
>> >>>     )
>> >>>     envo.Program('hello', 'hello.c')
>> >>>
>> >>> Note: Don't try to Append() to an OverrideEnvironment; that call is
>> >>> proxied to the underlying environment which would then be modified.
>> >>> (This is possibly a bug.)
>> >>>
>> >>> Hope this helps,
>> >>> Jonathon
>> >>> On Wed, Sep 5, 2018 at 7:50 PM RW via Scons-users <
>> scons-users at scons.org> wrote:
>> >>> >
>> >>> > Hi,
>> >>> > I was wondering, I know standard Makefiles have a way of specifying
>> flags for a given file before the target / rule is defined
>> >>> >
>> >>> > such as
>> >>> > $(PY_BUILD)/nlr%.o: CFLAGS += -Os
>> >>> >
>> >>> > is this possible in scons? or is the only way to pass in custom env
>> variables per target is when the target is defined?
>> >>> > https://www.scons.org/doc/latest/HTML/scons-user/ch03s09.html
>> >>> >
>> >>> > such as
>> >>> > env.Program('hello', 'hello.c', CFLAGS=['-Os'])
>> >>> >
>> >>> > Also the way the docs read I think it doesn't make it clear if your
>> appending or replacing values in the environment variable (e.g. CFLAGS) for
>> that specific target (I'm assuming replacing)
>> >>> >
>> >>> > I've been trying to see if I could port the Makefiles from
>> micropython across to scons btw, but as an initial step I've been trying to
>> keep the logic the same without changing the order of things too much
>> >>> >
>> >>> > Many Thanks
>> >>> > Richard
>> >>> > _______________________________________________
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