Functions with extermely long names can cause wasm-bindgen to fail to locate the main function

[sapphire-arches]

Describe the Bug

When a WASM module contains a function with an extremely long mangled name (>100_000 characters, as can be generated by rust-lang/rust#109363) wasmparser will choke on the names custom section. This means that at the walrus/wasm-bindgen layer any functions in the module after the problematically named function will not have names assigned. This is particularly deleterious if main is late, as it means wasm-bindgen won't emit the main glue (__wbindgen_start and friends).

Steps to Reproduce

1. Use the example code from Exponential blowup in core::drop_in_place symbol size for builder-pattern structures that chain closures rust-lang/rust#109363, or clone https://github.com/bobtwinkles/wasm-bindgen-bug/
2. Build that code with the module name bad or baad and rustc 1.66 - 1.70 (other versions not tested). The module name good happens to work but it's up to the order rustc chooses to emit the code, I'll chalk this one up to nominative determinism.

Expected Behavior

wasm-bindgen should maybe complain louder that it has failed to load all function names? I'm not really sure what can be done about this at the wasm-bindgen layer to be honest, I'm mostly just filing this bug here because I'm not sure what layer of the stack is really at fault here and want somewhere to anchor the discussion.

Actual Behavior

wasm-bindgen silently fails to generate main glue.

Additional Context

I discovered this while working on a Sycamore app, in particular the sycamore::builder::ElementBuilder type suffers from the exponential drop glue function symbol size problem mentioned in the Rust bug above.

[Liamolucko]

Huh, that's strange. The limit on function name lengths in wasmparser is intentional:

https://github.com/bytecodealliance/wasm-tools/blob/7108f5530dda9a07f5087ce4d013730b432438bc/crates/wasmparser/src/limits.rs#L26

But I'm not sure why it's getting silently ignored.

[sapphire-arches]

walrus treats failure to parse the name section as nonfatal: https://github.com/rustwasm/walrus/blob/9d6c9de432d6a97478dc76ebdf18aed51584c3af/src/module/mod.rs#L217-L231

so wasm-bindgen thinks all the names have been parsed successfully when they have not. Running wasm-bindgen with RUSTLOG=warn or greater will print that warning on the offending modules.