Start migrating some Wasmtime crates to no_std #8463
Merged
Commits on Apr 25, 2024
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Start migrating some Wasmtime crates to no_std
This commit is the first in what will be multiple PRs to migrate Wasmtime to being compatible with `#![no_std]`. This work is outlined in bytecodealliance#8341 and the rough plan I have in mind is to go on a crate-by-crate basis and use CI as a "ratchet" to ensure that `no_std` compat is preserved. In that sense this PR is a bit of a template for future PRs. This PR migrates a few small crates to `no_std`, basically those that need no changes beyond simply adding the attribute. The nontrivial parts introduced in this PR are: * CI is introduced to verify that a subset of crates can indeed be built on a `no_std` target. The target selected is `x86_64-unknown-none` which is known to not have `std` and will result in a build error if it's attempted to be used. * The `anyhow` crate, which `wasmtime-jit-icache-coherence` now depends on, has its `std` feature disabled by default in Wasmtime's workspace. This means that some crates which require `std` now need to explicitly enable the feature, but it means that by-default its usage is appropriate for `no_std`. The first point should provide CI checks that compatibility with `no_std` indeed works, at least from an "it compiles" perspective. Note that it's not sufficient to test with a target like `x86_64-unknown-linux-gnu` because `extern crate std` will work on that target, even when `#![no_std]` is active. The second point however is likely to increase maintenance burden in Wasmtime unfortunately. Namely we'll inevitably, either here or in the future, forget to turn on some feature for some crate that's not covered in CI checks. While I've tried to do my best here in covering it there's no guarantee that everything will work and the combinatorial explosion of what could be checked in CI can't all be added to CI. Instead we'll have to rely on bug fixes, users, and perhaps point releases to add more use cases to CI over time as we see fit.
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