Minimal implementation of fixed-length lists to enable wit-bindgen runtime tests

[cpetig]

Implement the necessary parts of fixed size lists (see WebAssembly/component-model#384 ) to enable runtime testing in wit-bindgen.

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[cpetig]

The best test for this functionality are the tests added to wit-bindgen in bytecodealliance/wit-bindgen#1277 .

I can create a test for this one as well (I didn't find a good template in the existing tests), but perhaps it makes most sense to introduce tests together with the host support in #12315 .

[alexcrichton]

Would it be possible to add a sample *.wast test which exercises this?

[cpetig]

Would it be possible to add a sample *.wast test which exercises this?

I guess it would be possible to make a two sub-component example which externally only offers a single boolean returning function, anything beyond this will depend on #12315 (e.g. passing an array to a function and checking the round-trip result).

Judging from the amount of errors uncovered by a single wit-bindgen test I think list-minmax16: func(a: list<u16, 4>, b: list<s16, 4>) -> tuple<list<u16, 4>, list<s16, 4>>; is the signature to test here 😉 (arguments are on stack, result is in memory and the tuple exercises offsets)

[alexcrichton]

That sounds reasonable to me yeah, and I think it's fine to expand the test coverage over time but I also think it'd be good to test what we can in this PR itself (which is, as you say, the composed-in-the-middle use)

[cpetig]

I added a moderately readable test (created in C++, then stripped down to 400 lines of wat).

Though, I was unable to get ;;! component_model_fixed_size_lists = true recognized by the wast test runner.

Could it be that it usually sets properties according to the path of the test? Or is it supposed to work and I just missed something?

[cpetig]

Oh, that is a new to me error in CI:

thread '<unnamed>' (24806) panicked at crates/environ/src/component/translate/adapt.rs:245:14:
invalid adapter module generated: multiple memories (at offset 0x5d)

I guess I need to take a deeper look tomorrow.

PS: The error on my computer is

Error: failed to run script file 'fixed_size_list.wast'

Caused by:
    0: failed directive on fixed_size_list.wast:17
    1: failed to parse WebAssembly module
    2: Fixed size lists require the component model fixed size list feature (at offset 0x16)

wasmtime wast -W component-model-fixed-size-lists fixed_size_list.wast works for me...

[alexcrichton]

Oh for that you'll want to add multi_memory = true at the top of the file. Not needed on the CLI because that inherits the default feature set, but during tests we turn off all features and require them to be explicitly turned on in files

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[cpetig]

Oh for that you'll want to add multi_memory = true at the top of the file. Not needed on the CLI because that inherits the default feature set, but during tests we turn off all features and require them to be explicitly turned on in files

My assumption was that this is caused by the component to component copying code https://github.com/bytecodealliance/wasmtime/pull/10619/files#diff-32f96d31ce61f8177ede00faf17bc565a8d15a00d42eb20b28a948a7a257dd87R2885-R2953 - I would assume that all adapters need multi-memory to work.

[cpetig]

My assumption was that this is caused by the component to component copying code https://github.com/bytecodealliance/wasmtime/pull/10619/files#diff-32f96d31ce61f8177ede00faf17bc565a8d15a00d42eb20b28a948a7a257dd87R2885-R2953 - I would assume that all adapters need multi-memory to work.

I was looking for wasmtime wast to pick up the setting and didn't realize that the test runner takes care of this. Should work now. Thank you for the tip, Alex.

[cpetig]

😊 Oh, I took a look whether "fixed-size-list" or "fixed-size-lists" is the name in the component spec, it is "fixed-length lists". So, I made sure that wasmtime adheres to the standard name.

Whether/how to change wasm-tools will be a separate discussion.