wasm32 and wasm64: default library borrow facts, -mm=gc refused, a JS host and test runs - #811

wasm32 and wasm64 programs, linked with the default library and tested under Node. Goes with ASDAlexander77/TypeScriptCompilerDefaultLib#92, which builds the wasm default library.

Compiler

• Own borrow facts from a wasm archive (ObjDumper.cpp): a wasm data symbol is an offset into its data segment, but it was read at that offset into the whole DATA section, whose contents start with the segment headers. An -mm=own program linked with the wasm default library therefore got none of the library's borrow facts and failed to compile.
• An override of another arity (MLIRGenStore.h, MLIRGenClasses.cpp): an override such as get(scale?) of an abstract get(), or foo() of foo(x, y, ...z), was stored in the base method's vtable slot unchanged. Native code tolerates that; wasm's call_indirect checks the signature and traps. Now, as in C++, the override gets a slot of its own type. Each inherited slot holds a thunk of the slot's type, which passes undefined for a missing optional parameter and an empty array for a missing rest parameter, and drops extra arguments. New test: 00class_override_arity.
• -mm=gc refused for wasm: gc is tslang's default, so a wasm executable or library now has to name another memory model. The error says so: the collector has no wasm build. Before, the link failed on a default-library folder that is never built.

Host and test runs (docs/how/wasm/test)

• host.mjs: the imports a wasm program takes from env, which on other targets come from the C library and the default library's wrappers:
  • printf-family formatting, strtod/strtol, a heap
  • regex (JS RegExp), time and strftime
  • stdio and stdin
  • process and fs under Node
  • pointers and size_t as BigInt on wasm64
• run.mjs runs one program under Node; index.html runs a folder of programs in a browser with the same host.
• run_tests.mjs runs two suites for wasm32 and wasm64 under none, rc and own, in release (--opt) or debug (--debug):
  • tester: the tester's single-file ctest tests, built --no-default-lib as test-runner builds them. A test passes on done. and exit code 0.
  • defaultlib: the default library's tests, linked with the wasm default library. A test passes on ALL DONE, an empty stderr and exit code 0.
• wasm64 needs Node 24 or later, because LLVM emits table64.

Results (Node 26, release and debug)

• tester: 569 (wasm32) and 570 (wasm64) pass under none and rc, 0 fail. Under own, 419 pass and 0 fail; another 148–149 tests do not compile natively under own either.
• defaultlib: 181 pass under none and rc, 180 under own, 0 fail, on both triples.
• Native ctest: 6964/6964.

Skipped, and still open

Each skip is listed with its reason:

• try/catch (64 tests): there are no landing pads on wasm yet, so a throw ends the program.
• async: there is no async runtime for wasm.
• threads.

wasm_skips.txt lists the open wasm compiler gaps:

• 00object_func2: a method stored in an object's field is called as a function with this plus the object, but it takes only this. call_indirect checks the signature, so the call traps.
• wasm32: the interface accessor-cell tag addr + 0x80000000 is folded into an i32.const, and wasm-ld fails with "LEB is outside Varint32 range".
• wasm64: wasm-ld fails with "invalid data relocation" for a generator's next.
• path.ts: a Readonly<Path> field read through Maybe<...> comes back wrong, and the loop never ends.

Also seen: 00owned_iteration failed once in a full wasm64 debug run. It then passed three times on its own.

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