Again, this is not complete and is just enough for backend.py. Again,
typing these is complicated massively by the layering violations in the
Target classes and the interpreter.
This is not complete, it's just enough for backend/backend.py. A more
completely typing would be more difficult, especially whithout
untangling the layering violation between the build targets and the
interpreter.
The problem is what happens in this case:
```meson
add_project_arguments('-DHOST', language : 'c', native : false)
add_project_arguments('-DBUILD', langauge : 'c', native : true)
```
The original meson behavior was that in an host == build configuration
only the `native : false` would be applied. This doesn't really make
sense as in that case the build machine is the host machine, so it is
both the native and non-native machine at once. We changed this so that
the both would be applied in a host == build configuration, but this is
a behavioral change, and needs to be reverted.
Fixes: #9037
This commit introduces a new type of `HoldableObject`: The
`SecondLevelHolder`. The primary purpose of this class is
to handle cases where two (or more) `HoldableObject`s are
stored at the same time (with one default object). The
best (and currently only) example here is the `BothLibraries`
class.
There's no reason to allow None into the backend, it already has code to
check that all of the values of the FileMode object are None, so let's
use that, which is much simpler all the way down.
As seen in the testcase, passing objects to custom_target does not work
if headers are passed extract_objects(), or if extract_all_objects() is used
and the sources include any header files. To fix this, use the code that
already exists for unity build to filter out the nonexistent ".h.o" files.
This already gives for free the handling of genlist, which was mentioned
in a TODO comment.
For qt we already have all of the necissary checking in place. Now in
the interpreter we have the same, the intrperter does all of the
checking, then passed the arguments to the Generator initializer, which
just assigns the passed values. This is nice, neat, and clean and fixes
the layering violatino between build and interpreter.
Dylan Baker
Xavier Claessens
Marc-André Lureau
Simon Ser
Daniel Mensinger
Paolo Bonzini
Eli Schwartz