Equivalent of recursive make with meson/ninja?

[Sébastien Wilmet <swilmet gnome org>]

Hi,

With the Autotools, recursive make is very convenient to re-build only
the stuff present in a sub-directory.

And with builddir == srcdir, it's convenient to do things like:
$ cd src/
$ make
$ touch file-that-i-modified.c
$ make

To see the warnings only for the file that I modified.

(see also this thread for more details on my workflow:
https://mail.gnome.org/archives/desktop-devel-list/2016-August/msg00047.html
"builddir != srcdir in jhbuild breaks my workflow")

I've tried this command in a project using meson:
```
$ meson .
Error during basic setup:

Source and build directories must not be the same. Create a pristine build directory.
```

So meson doesn't support builddir == srcdir. This is a no-go for me. And
I suppose meson/ninja doesn't support recursive ninja either (and anyway
recursive ninja with builddir != srcdir would not be convenient).

It's a pity, because meson on the paper looks nice, with faster build
and multiplatform support (including Visual Studio, currently with the
Autotools some GNOME projects have a separate build/win32/ directory to
support Visual Studio).

So, that's it, I think I'll continue to use the Autotools in my projects
for the foreseeable future.

--
Sébastien