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Handle OOM in Engine::new #12362

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@fitzgen fitzgen commented Jan 15, 2026

Part of #12069

Depends on #12361

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Introduce wasmtime_environ::collections::{OomArc, OomBox}
92f9d35 
These types mirror their `std`/`alloc` counterparts, but only provide fallible
constructors and properly handle OOM by returning `Err(OutOfMemory)`.

Note that stable Rust doesn't actually give us any method to build fallible
allocation for `Arc<T>`, and we do not wish to fork `Arc<T>` since it is full of
very subtle unsafe code, so `OomArc::new` is only actually fallible in practice
when using nightly Rust and setting `RUSTFLAGS="--cfg arc_try_new"` during the
build. We use a custom `cfg`, rather than a cargo feature, so that `cargo test
--all-features --workspace` (which is morally what CI does) continues to Just
Work in the workspace, same as we do for e.g. Pulley's usage of the nightly Rust
tail calls feature.

Part of bytecodealliance#12069
@fitzgen fitzgen requested review from a team as code owners January 15, 2026 19:39
@fitzgen fitzgen requested review from alexcrichton and removed request for a team January 15, 2026 19:39
@fitzgen fitzgen force-pushed the handle-oom-in-engine-new branch from 420d352 to 62d45c5 Compare January 15, 2026 20:48
@github-actions github-actions bot added fuzzing Issues related to our fuzzing infrastructure wasmtime:api Related to the API of the `wasmtime` crate itself wasmtime:config Issues related to the configuration of Wasmtime labels Jan 15, 2026
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Label Messager: wasmtime:config

It looks like you are changing Wasmtime's configuration options. Make sure to
complete this check list:

  • If you added a new Config method, you wrote extensive documentation for
    it.

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information about not just the method, but its parameters and results as
well.

Is this method fallible? If so, when can it return an error?

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  • If you added a new Config method, or modified an existing one, you
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