[Scons-users] Problems with SConscript files using variant_dir and duplicate=False

[Daniel Moody]

the docs say:  https://scons.org/doc/3.1.2/HTML/scons-man.html#f-SConscript
"The variant_dir argument is interpreted relative to the directory of the
calling SConscript file."

So in the case the SConstruct is the "calling SConscript" and you are
saying the variant dir for the SConscript should be target/mylib, but its
not, its ../../target/mylib relative to the calling SConstruct.

So you need to call it like this:
mylib_a, mylib_h = SConscript('../../SConscript', exports='env', variant_dir
='../../target/mylib', duplicate=False)

For a non duplicated variant dir, the variant dir will be substituted with
the source dir when resolving paths for the build, which means
substituting "target/mylib/include" to "./include" where 'target/mylib' is
the variant dir and '.' is the source dir, will not work from the calling
SConstructs location. It should be substituted with "../../target/mylib" so
the variant dir resolved to the correct location.

On Thu, May 21, 2020 at 12:54 PM Hans-Christian Wild <hchr.wild at gmail.com>
wrote:

> Hi,
>
> I have two questions about SCons, I have uploaded a *working* example as
> base where SCons does everything nearly as I want it. The problems start to
> occur only when we do slight modifications to this example.
>
> https://github.com/hchrwild/scons01/tree/master
>
> In the project we have a main SConstruct file in `/example/mingw/` which
> imports a library SConscript file from `/`. The SConscript file creates its
> little library for the given environment and returns it together with its
> public header include path. The SConstruct file in turn builds an
> executable linking the static library and using the public header include
> path.
>
> Output:
>
> scons: Reading SConscript files ...
> scons: done reading SConscript files.
> scons: Building targets ...
> scons: building associated VariantDir targets: target\mylib\example\mingw
> gcc -o target\src\main.obj -c -Itarget\mylib\include target\src\main.c
> gcc -o target\mylib\src\Assert.obj -c -Itarget\mylib\include
> -Itarget\mylib\src\include target\mylib\src\Assert.c
> ar rc target\mylib\libmylib.a target\mylib\src\Assert.obj
> gcc -o target\mingw-example.exe target\src\main.obj target\mylib\libmylib.a
> scons: done building targets.
>
> *Perfect!*
> (Although I don't understand why it prints `building associated VariantDir
> targets: *target\mylib\example\mingw*` which to me does not make sense,
> IMO it should be *`example/mingw/target/mylib`* if anything, but let's
> put that aside..)
>
> *Now the actual problems:*
>
> 1) I don't like that SCons duplicates everything. What I really want is an
> out-of-source variant build. When I set `duplicate=False`, the build fails,
> however:
>
> mylib_a, mylib_h = SConscript('../../SConscript', exports='env',
> variant_dir='target/mylib', duplicate=False)
>
> scons: Reading SConscript files ...
> scons: done reading SConscript files.
> scons: Building targets ...
> scons: building associated VariantDir targets: .
> gcc -o target\src\main.obj -c *-Itarget\mylib\include* target\src\main.c
> target\src\main.c:4:10: fatal error: Types.h: No such file or directory
>  #include <Types.h>
>           ^~~~~~~~~
> compilation terminated.
> scons: *** [target\src\main.obj] Error 1
> scons: building terminated because of errors.
>
> As marked in above output, the include path is not updated. The SConscript
> file is at `../../` relative to SConstruct, and the include folder is
> ./include relative to SConscript. Therefore, without duplication, the
> correct include path relative to SConstruct would be `../../include` ,
> which SCons does not seem to compute however. Is this expected or a missing
> feature/bug? I really like the idea, that the SConstruct file really only
> needs to know where the SConscript file is located and having everything
> else being figured out by the build system...
>
> 2) Let's put that aside and keep above change, but hardcode the expected
> include path in SConstruct file:
>
> program = env.Program('target/mingw-example', sources, CPPPATH=[
> '../../include'], LIBS=[mylib_a])
>
> scons: Reading SConscript files ...
> scons: done reading SConscript files.
> scons: Building targets ...
> scons: building associated VariantDir targets: .
> gcc -o target\src\main.obj -c -IW:\Projects\mylib\include target\src\main.c
> gcc -o target\mylib\src\Assert.obj -c *-Itarget\mylib\include
> -IW:\Projects\mylib\include -Itarget\mylib\src\include
> -IW:\Projects\mylib\src\include* W:\Projects\mylib\src\Assert.c
> ar rc target\mylib\libmylib.a target\mylib\src\Assert.obj
> gcc -o target\mingw-example.exe target\src\main.obj target\mylib\libmylib.a
> scons: done building targets.
>
> Now the compilation succeeds. However, scons has now duplicated the
> include paths for the static library! One time with the invalid
> variant-with-duplication path, and one time with the correct (absolute
> path). Why does it do that? Is this a bug?
>
> Sorry for the long post. Any feedback appreciated!
>
> -hans
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