WebAssembly does not support runtime checking of isolated conformances

[DougGregor]

Description

Isolated conformance checking at runtime is currently disabled in WebAssembly, as indicated by this disabled runtime test. The underlying problem is that we WebAssembly doesn't have __attribute__((constructor)) support on the C side, so the concurrency setup doesn't get executed. We'll need to find some way to run that setup code for WebAssembly, e.g., by injecting a call to the setup function from the compiler.

Reproduction

Re-enable the test linked above for WebAssembly.

Expected behavior

Test should be enabled and run,

Environment

Swift main, 6.2

Additional information

No response

[MaxDesiatov]

wasm-ld supports WASM_INIT_FUNCS custom linking metadata sections and in linking modes that we're interested in these functions should be called from entrypoint functions per https://github.com/WebAssembly/tool-conventions/blob/3822c2b4365ac2849c85ea078d7679ed896f2fd2/BasicModuleABI.md?plain=1#L12

So it seems like it's on Clang to support __attribute__((constructor)) if it doesn't do so yet. IIUC the underlying facilities for that are present.

[MaxDesiatov]

cc @kateinoigakukun

[kateinoigakukun]

Yes, wasm-ld definitely has ctor support. I suspect the ctor definition is not retained in the final image because it's defined in a separate object file Setup.cpp.o and there is no other symbol in the object.
So I guess the root problem here is not specific to Wasm but generally problematic when linking libswift_Concurrency statically. (but I haven't locally checked the issue yet)