SCons: Disable C++ exception handling by default

[akien-mga]

Counterpart to godotengine/godot#80612.

Didn't test it, neither SCons nor CMake changes.

[dsnopek]

Thanks!

Given that this was merged in Godot, it makes sense that we do it here too!

The tests pass, which is good. Skimming the Godot changes, the scons changes here look comparable. The one thing I'm worried about is if it's easy enough for a GDExtension that's using godot-cpp's SConstruct file to disable "disable_exceptions", since this isn't really an end-developer setting, but something the extension author want to set. @adamscott has been adding a number of changes along this line, and I'd like to try and test this when I get a chance.

Unfortunately, I don't know cmake and can't really review those changes.

[adamscott]

Here, the question is: "Are exceptions supported by gd-extension".

If so, we should make these changes optional. If not, let's go.

[dsnopek]

Here, the question is: "Are exceptions supported by gd-extension".

Whether or not to use exceptions depends on the specific GDExtension. If the GDExtension is integrating a 3rd party library into Godot that requires using exceptions, then they need to be enabled. Or, if the author of the GDException just likes exceptions and wants to use them in their own code.

So, I don't think folks will really use the command line argument: the particular GDExtension either needs exceptions or it doesn't. It'll really be the GDExtension author who is deciding to enable or disable them, and so I just want to make sure it's easy enough to do when the GDExtension's SConstruct includes the godot-cpp SConstruct.

[akien-mga]

I haven't tested it, but in theory you should be able to just do env["disable_exceptions"] = False to override what the end user may specify when compiling.

[dsnopek]

I didn't test the cmake changes, but they look OK. But I did test with scons and it didn't work without making a small change - see the code comments.

I also tried putting this in a GDExtension:

env['disable_exceptions'] = False

The code in godot-cpp still compiled (after making the CXXFLAGS change) with -fno-exceptions flag, but the user code in the GDExtension didn't, which is actually probably what we want, so I think this fine in that regard.

[dsnopek]

Fabio and I did some testing, and we think the CCFLAGS issue may be fixed now, probably by some other refactoring that we've done here. In any case, it probably still does make sense to put it in CXXFLAGS because it's a C++ specific options.

However, this will need to be rebased now that this code has moved to godotcpp.py.

@akien-mga Are you still interested in working on this one? Or, should one of us take it over?

[akien-mga]

I can update it tomorrow. I'll also have to update upstream Godot accordingly if we change it to CXXFLAGS, to stay consistent.

[akien-mga]

Rebased. Didn't compile to test though.

[dsnopek]

I tested this with scons and it does add -fno-exceptions like expected, and running with scons disable_exceptions=no works too.

However, I wasn't able to find a way to re-enable exceptions in a SConstruct that uses the godot-cpp SConstruct. So, the idea is, if a developer makes a GDExtension that needs exceptions, they'll want their SConstruct to enable them, without having to tell users to run scons disable_exceptions=no. I tried doing:

env = SConscript("godot-cpp/SConstruct")
env['disable_exceptions'] = False

... and:

env = Environment()
env['disable_exceptions'] = False
Export('env')

SConscript("godot-cpp/SConstruct")

... and a bunch of variations on that, like:

SConscript("godot-cpp/SConstruct", exports=['env'])

... and:

SConscript("godot-cpp/SConstruct", exports={'disable_exceptions': False'})

But nothing I tried allowed me to pass that option down into godot-cpp's SConstruct. Based on my earlier comment above it seems I got this to work on an earlier version? Perhaps, it's moving to the tools/godotcpp.py that's changed things?

[Faless]

@dsnopek the second option, i.e.:

env = Environment()
env['disable_exceptions'] = False
Export('env')

SConscript("godot-cpp/SConstruct")

should work after applying my suggestion above

[dsnopek]

It's working great in my testing now! Thanks!

[Faless]

LGTM 👍

[dsnopek]

Thanks!

[dsnopek]

Cherry-picked for 4.1 in PR #1281