* Return `anyhow::Error` from host functions instead of `Trap`
This commit refactors how errors are modeled when returned from host
functions and additionally refactors how custom errors work with `Trap`.
At a high level functions in Wasmtime that previously worked with
`Result<T, Trap>` now work with `Result<T>` instead where the error is
`anyhow::Error`. This includes functions such as:
* Host-defined functions in a `Linker<T>`
* `TypedFunc::call`
* Host-related callbacks like call hooks
Errors are now modeled primarily as `anyhow::Error` throughout Wasmtime.
This subsequently removes the need for `Trap` to have the ability to
represent all host-defined errors as it previously did. Consequently the
`From` implementations for any error into a `Trap` have been removed
here and the only embedder-defined way to create a `Trap` is to use
`Trap::new` with a custom string.
After this commit the distinction between a `Trap` and a host error is
the wasm backtrace that it contains. Previously all errors in host
functions would flow through a `Trap` and get a wasm backtrace attached
to them, but now this only happens if a `Trap` itself is created meaning
that arbitrary host-defined errors flowing from a host import to the
other side won't get backtraces attached. Some internals of Wasmtime
itself were updated or preserved to use `Trap::new` to capture a
backtrace where it seemed useful, such as when fuel runs out.
The main motivation for this commit is that it now enables hosts to
thread a concrete error type from a host function all the way through to
where a wasm function was invoked. Previously this could not be done
since the host error was wrapped in a `Trap` that didn't provide the
ability to get at the internals.
A consequence of this commit is that when a host error is returned that
isn't a `Trap` we'll capture a backtrace and then won't have a `Trap` to
attach it to. To avoid losing the contextual information this commit
uses the `Error::context` method to attach the backtrace as contextual
information to ensure that the backtrace is itself not lost.
This is a breaking change for likely all users of Wasmtime, but it's
hoped to be a relatively minor change to workaround. Most use cases can
likely change `-> Result<T, Trap>` to `-> Result<T>` and otherwise
explicit creation of a `Trap` is largely no longer necessary.
* Fix some doc links
* add some tests and make a backtrace type public (#55)
* Trap: avoid a trailing newline in the Display impl
which in turn ends up with three newlines between the end of the
backtrace and the `Caused by` in the anyhow Debug impl
* make BacktraceContext pub, and add tests showing downcasting behavior of anyhow::Error to traps or backtraces
* Remove now-unnecesary `Trap` downcasts in `Linker::module`
* Fix test output expectations
* Remove `Trap::i32_exit`
This commit removes special-handling in the `wasmtime::Trap` type for
the i32 exit code required by WASI. This is now instead modeled as a
specific `I32Exit` error type in the `wasmtime-wasi` crate which is
returned by the `proc_exit` hostcall. Embedders which previously tested
for i32 exits now downcast to the `I32Exit` value.
* Remove the `Trap::new` constructor
This commit removes the ability to create a trap with an arbitrary error
message. The purpose of this commit is to continue the prior trend of
leaning into the `anyhow::Error` type instead of trying to recreate it
with `Trap`. A subsequent simplification to `Trap` after this commit is
that `Trap` will simply be an `enum` of trap codes with no extra
information. This commit is doubly-motivated by the desire to always use
the new `BacktraceContext` type instead of sometimes using that and
sometimes using `Trap`.
Most of the changes here were around updating `Trap::new` calls to
`bail!` calls instead. Tests which assert particular error messages
additionally often needed to use the `:?` formatter instead of the `{}`
formatter because the prior formats the whole `anyhow::Error` and the
latter only formats the top-most error, which now contains the
backtrace.
* Merge `Trap` and `TrapCode`
With prior refactorings there's no more need for `Trap` to be opaque or
otherwise contain a backtrace. This commit parse down `Trap` to simply
an `enum` which was the old `TrapCode`. All various tests and such were
updated to handle this.
The main consequence of this commit is that all errors have a
`BacktraceContext` context attached to them. This unfortunately means
that the backtrace is printed first before the error message or trap
code, but given all the prior simplifications that seems worth it at
this time.
* Rename `BacktraceContext` to `WasmBacktrace`
This feels like a better name given how this has turned out, and
additionally this commit removes having both `WasmBacktrace` and
`BacktraceContext`.
* Soup up documentation for errors and traps
* Fix build of the C API
Co-authored-by: Pat Hickey <pat@moreproductive.org>
* Optimize `Func::call` and its C API
This commit is an alternative to #3298 which achieves effectively the
same goal of optimizing the `Func::call` API as well as its C API
sibling of `wasmtime_func_call`. The strategy taken here is different
than #3298 though where a new API isn't created, rather a small tweak to
an existing API is done. Specifically this commit handles the major
sources of slowness with `Func::call` with:
* Looking up the type of a function, to typecheck the arguments with and
use to guide how the results should be loaded, no longer hits the
rwlock in the `Engine` but instead each `Func` contains its own
`FuncType`. This can be an unnecessary allocation for funcs not used
with `Func::call`, so this is a downside of this implementation
relative to #3298. A mitigating factor, though, is that instance
exports are loaded lazily into the `Store` and in theory not too many
funcs are active in the store as `Func` objects.
* Temporary storage is amortized with a long-lived `Vec` in the `Store`
rather than allocating a new vector on each call. This is basically
the same strategy as #3294 only applied to different types in
different places. Specifically `wasmtime::Store` now retains a
`Vec<u128>` for `Func::call`, and the C API retains a `Vec<Val>` for
calling `Func::call`.
* Finally, an API breaking change is made to `Func::call` and its type
signature (as well as `Func::call_async`). Instead of returning
`Box<[Val]>` as it did before this function now takes a
`results: &mut [Val]` parameter. This allows the caller to manage the
allocation and we can amortize-remove it in `wasmtime_func_call` by
using space after the parameters in the `Vec<Val>` we're passing in.
This change is naturally a breaking change and we'll want to consider
it carefully, but mitigating factors are that most embeddings are
likely using `TypedFunc::call` instead and this signature taking a
mutable slice better aligns with `Func::new` which receives a mutable
slice for the results.
Overall this change, in the benchmark of "call a nop function from the C
API" is not quite as good as #3298. It's still a bit slower, on the
order of 15ns, because there's lots of capacity checks around vectors
and the type checks are slightly less optimized than before. Overall
though this is still significantly better than today because allocations
and the rwlock to acquire the type information are both avoided. I
personally feel that this change is the best to do because it has less
of an API impact than #3298.
* Rebase issues
sync test: show the dummy executor will trap (rather than panic) when a
future inside it pends.
async test: show that the executor is hooked up to a future that pends
for a trivial amount of time.
this adds tokio to the dev-dependencies of wiggle, it shouldn't end up
increasing the build burden for the project as a whole since its already
a dev-dependency.
* Update wasm-tools crates
This brings in recent updates, notably including more improvements to
wasm-smith which will hopefully help exercise non-trapping wasm more.
* Fix some wat
Implement Wasmtime's new API as designed by RFC 11. This is quite a large commit which has had lots of discussion externally, so for more information it's best to read the RFC thread and the PR thread.
