Wasmtime component bindgen: opt-in trappable error types #5397
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| struct MyImports {} | ||
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| impl imports::Imports for MyImports { | ||
| fn empty_error(&mut self, a: f64) -> Result<Result<f64, ()>, Error> { |
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Oh I thought the Error<T> was going to work which would avoid this result-of-result, but could you explain a bit more why it didn't work out?
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I just don't have any tests that actually use the functionality in yet. I wanted to get this "trivial" behavior working with the new test scheme before I put in the more complicated stuff.
We can't use Result<f64, Error<()>> in this case because Error requires T impl std::error::Error. Additionally, all of this PR only supports substituting named types, and doesn't support substituting primitive types.
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Ah ok makes sense. I'm worried about the ergonomics of this, though. Are you thinking we'd special-case -> result<T, rich-error> in WIT to have a Result<T, E> return value here? For degenerate cases like -> result<T> with no error or primitive errors I'm fine with doing whatever.
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I put the tests in below that show we can special case a interface i { ... result<t, e> } to Result<T, TrappableE> when the user invokes the macro with trappable_error_types: { i::e: TrappableE, ... }
crates/wit-bindgen/src/lib.rs
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| #[cfg(feature = "clap")] | |||
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Oh all this clap stuff is a holdover from copying over from the wit-bindgen repository, I think all of it can be removed since clap isn't even a dependency in this repo.
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Oh! I didn't even think to look. Deleted.
these are not used - clap isnt even an optional dep here - but were a holdover from the old home
This was gotten working over in wit-bindgen, and I ported it to the wasmtime repo since the generator moved.
My earlier failed experiment of a "HostError" has been deleted, and bindgen macro users can now opt in to a special
trappable_error_typewhich should work exactly how wiggle's trappable errors work.When the user provides the macro argument
the code generator looks in wit interfaces named
ifor a wit type namede, it will generate a typestruct TrappableEwhichimpl Errorandimpl From<E> for TrappableE. In any functions that returnresult<t, e>, it generates the return typeResult<T, TrappableE>, rather than the much less idiomaticResult<Result<T, E>, anyhow::Error>.I introduced new tests in
tests/all/component-model/bindgen/results.rsthat show this functionality in use.