[Scons-users] How to turn off source scanner

[Jason Kenny]

Hi Bill,

Changing the code to:

env2=env.Clone(SCANNERS=[])
env2.Command(..

seems to work.

However

env.Command(
    […],
    […],
    "autoreconf -if && ./configure\
     CC=${CC} CXX=${CXX}\
     ",
     SCANNERS=[]
)

Does not. I would have thought that the environment override would have worked here. It does not to my surprise

It does looks like adding a

env.Command(
    […],
    […],
    "autoreconf -if && ./configure\
     CC=${CC} CXX=${CXX}\
     ",
     source_scanner=Scanner(
                function = lambda *lst,**kw: [],
                )
)

Works.

Thanks … moving on to the next issue.

Jason


From: Scons-users <scons-users-bounces at scons.org> On Behalf Of Bill Deegan
Sent: Wednesday, February 6, 2019 9:40 PM
To: SCons users mailing list <scons-users at scons.org>
Subject: Re: [Scons-users] How to turn off source scanner

From manpage:
SCANNERS

A list of the available implicit dependency scanners. New file scanners may be added by appending to this list, although the more flexible approach is to associate scanners with a specific Builder. See the sections "Builder Objects" and "Scanner Objects," below, for more information.
Create a new environment and empty this variable? Use that environment for your command?

Does that work?

On Wed, Feb 6, 2019 at 9:31 PM Jason Kenny <dragon512 at live.com<mailto:dragon512 at live.com>> wrote:

Looking how to turn off a scanner for a build command.

Simple reproducer..

Run:
Git clone https://github.com/libunwind/libunwind.git<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Flibunwind%2Flibunwind.git&data=02%7C01%7C%7C2867dfe9f89a4a7b9fb708d68cae03a2%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636851076338526850&sdata=u%2BEbJu10%2Bi8DhnvCwJuiK%2FBDKMfmFxHi51fCLnmLSoc%3D&reserved=0>

In the libunwind folder add a Sconstruct with this content

env = Environment()
env.Command(
    ["Makefile"],
    [
        "include/compiler.h",
        "include/dwarf-eh.h",
        "include/dwarf.h",
        "include/dwarf_i.h",
        "include/libunwind-aarch64.h",
        "include/libunwind-arm.h",
        "include/libunwind-common.h.in<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Flibunwind-common.h.in&data=02%7C01%7C%7C2867dfe9f89a4a7b9fb708d68cae03a2%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636851076338536860&sdata=eGTdDeMwFiS3IKq2hYb4lw16ZI032kvlgjmFo92754k%3D&reserved=0>",
        "include/libunwind-coredump.h",
        "include/libunwind-dynamic.h",
        "include/libunwind.h.in<https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Flibunwind.h.in&data=02%7C01%7C%7C2867dfe9f89a4a7b9fb708d68cae03a2%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636851076338546865&sdata=OXAhRrPx55EeUf9W1A%2FBPQuYVy5Xn2jnzfCMyCskJV4%3D&reserved=0>",
        "include/libunwind-hppa.h",
        "include/libunwind-ia64.h",
        "include/libunwind_i.h",
        "include/libunwind-mips.h",
        "include/libunwind-ppc32.h",
        "include/libunwind-ppc64.h",
        "include/libunwind-ptrace.h",
        "include/libunwind-sh.h",
        "include/libunwind-tilegx.h",
        "include/libunwind-x86_64.h",
        "include/libunwind-x86.h",
        "include/mempool.h",
        "include/remote.h",
        "include/unwind.h",
    ],
    "autoreconf -if && ./configure\
     CC=${CC} CXX=${CXX}\
     "
)

Then run
Scons

Then run
Scons –debug=explain -n

You should see something as:
…
scons: Building targets ...
scons: rebuilding `Makefile' because:
           `include/config.h' is a new dependency
           `include/libunwind.h' is a new dependency
           `include/libunwind-common.h' is a new dependency
           `include/tdep/libunwind_i.h' is a new dependency
autoreconf -if && ./configure CC=gcc CXX=g++
scons: done building targets.

The reason for this is that the Commands source is a list of header files. These header files have a scanner running on them. When the configure logic is finished the config.h and other headers are generated. This cause a false rebuild to happen.

I would like to prevent the false rebuild.
The more complex case based on a function I am trying to define to make it easy to call autoconf project from scons to build a larger mega project. The issue I am having is that in case as this libunwind would be a “leaf component” that is needed by many other components. This rebuild of the Makefile causes a chain of build action that make for annoying and long builds on the second pass that are not needed. Technically the Makefile does not need to be rebuilt because config.h was added. However I have not found a way to get this fixed.

I tired adding

env.Ignore(['Makefile'],
    [
        'include/config.h',
           'include/libunwind.h',
           'include/libunwind-common.h',
           'include/tdep/libunwind_i.h',
    ]
)

But this results in a message of:
scons: rebuilding `Makefile' because the dependency order changed:…

Do you have thoughts on how to fix this? My main thought is to turn off the c\c++ scanner for this builder. However I am unaware of a method to do this.

Jason
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