[Matheus28]

I love that I get to use python to write the dependency graph, it allows for some interesting stuff.

Other than that, it's mostly the ease of use. This is enough to compile a C++ project (that has all its .c and .cpp files in the same directory as the SConstruct file), and it'll pick up on all dependencies correctly:

    Program(target = 'a.out', source = Glob('*.c') + Glob('*.cpp'))

I also know for a fact that it's able to pick up on how the presence of a new file might trigger a rebuild of what could require it.

Regarding the last question, using --tree=all it prints:

    +-.
      +-SConstruct
      +-a.out
      | +-main.o
      | | +-main.c
      | | +-/usr/bin/gcc
      | +-/usr/bin/gcc
      +-main.c
      +-main.o
        +-main.c
        +-/usr/bin/gcc

I'm not sure if it's hiding dependencies on system headers or not. But I can force it to show them by adding /usr/include and /usr/local/include to CPPPATH (excuse the long code block):

    +-.
      +-SConstruct
      +-a.out
      | +-main.o
      | | +-main.c
      | | +-/usr/include/stdio.h
      | | +-/usr/include/Availability.h
      | | +-/usr/include/_types.h
      | | +-/usr/include/secure/_stdio.h
      | | +-/usr/include/sys/_types/_null.h
      | | +-/usr/include/sys/_types/_off_t.h
      | | +-/usr/include/sys/_types/_size_t.h
      | | +-/usr/include/sys/_types/_ssize_t.h
      | | +-/usr/include/sys/_types/_va_list.h
      | | +-/usr/include/sys/cdefs.h
      | | +-/usr/include/sys/stdio.h
      | | +-/usr/include/xlocale/_stdio.h
      | | +-/usr/include/AvailabilityInternal.h
      | | +-/usr/include/sys/_types.h
      | | +-/usr/include/secure/_common.h
      | | +-/usr/include/sys/_posix_availability.h
      | | +-/usr/include/sys/_symbol_aliasing.h
      | | +-/usr/include/machine/_types.h
      | | +-/usr/include/sys/_pthread/_pthread_types.h
      | | +-/usr/include/i386/_types.h
      | | +-/usr/bin/gcc
      | +-/usr/bin/gcc
      +-main.c
      +-main.o -- This part was removed to decrease comment size, it's the same as the main.o part above

The SConstruct for this last block is:

    Program(target = 'a.out', source = ['main.c'], CPPPATH = ['/usr/local/include', '/usr/include'])

Note that these were generated on macOS.

[JdeBP]

From what you are showing us, the answer to How does scons handle non-existence dependencies? is that it does not handle them at all.

Go and look at M. Moskopp's graph. It has a lot of dependencies for non-existent files that the compiler would have used in preference to the ones that it actually used, had they existed.