Allow exporting of symbols that are not valid JS identifiers

[sbc100]

In this case we now generate a warning instead of an errors.

Such symbols are not directly accessible in the module scope (since we cannot declare them there). They are only accessible via wasmExports or Module dictionary objects.

See: llvm/llvm-project#169043
Fixes: #24825, #23560

[dschuff]

Thanks this looks good, at least for the 2 emscripten bugs mentioned above. I'm still wondering about the Objc use case though. In particular, when symbols that begin with the dot will be generated and exported, and which ones. If the runtime will always have such symbols, there will basically be a warning everytime anyone ever links an objc program. So we might want some way to suppress the warning. Either just never emit the warning when linking objc, or some more selective way that can distinguish real warnings from others (not sure if that would be useful).

[sbc100]

Yes, we can consider removing the warning later, or finding a way to auto-suppress it. Obviously -Wno-js-compiler will suppress it but I think you are suggesting doing this automatically?

[dschuff]

If it's the case that every objc program contains exports from the stdlib that will trigger this warning, we probably don't want to be emitting a warning for every valid program.

[sbc100]

If it's the case that every objc program contains exports from the stdlib that will trigger this warning, we probably don't want to be emitting a warning for every valid program.

No, but you are right that we should fix llvm upstream so that these symbols are not exported by default.

I still think this change is worth landing interdependently of any ObjC.