Stream: git-wasmtime

Topic: wasmtime / issue #12783 c-api: `gc` feature unconditional...

Wasmtime GitHub notifications bot (Mar 16 2026 at 12:25):

leonm1 opened issue #12783:

In the c-api crate, the c-api specifies wasmtime as a dependency and explicitly enumerates its default features. Cargo permits overriding the features in a subdependency by explicitly passing the subdependency and a set of features, such as this:

[dependencies]
wasmtime = {version = "42.0.1", default-features = false, features = ['std', 'runtime']}
wasmtime-c-api-impl = {version = "42.0.1", features = ['cranelift']}

However, this is not able to _disable_ explicitly selected features of subdependencies (as default-features = false only applies to the features in the wasmtime crate's own Cargo.toml).

wasmtime's c-api crate already includes a feature to toggle gc, so the explicit inclusion of gc in the wasmtime's features is unnecessary. The fix would be to avoid specifying features for the wasmtime dependency in the c-api crate's Cargo.toml.

This change could be made backwards compatible by enabling the wasmtime c-api crate's gc feature by default, which would transitively enable wasmtime's gc feature in a way that could be disabled by consumers.

Related: https://github.com/proxy-wasm/proxy-wasm-cpp-host/pull/502#discussion_r2873328850

Wasmtime GitHub notifications bot (Mar 16 2026 at 15:52):

alexcrichton commented on issue #12783:

Thanks for the report! This is indeed currently the case, and it should be fine to change this whenever. It's ok to break back-compat, that's why Wasmtime has major version releases every month.

The fix for this is, in theory:

• Remove gc from this dependency directive
• Everywhere there's WASMTIME_FEATURE_LIST the gc feature is already listed, so nothing to do there (but maybe double check)
• Add a CI job which builds the C API without default features and with the gc feature to double-check it works.

Happy to review/help with a PR if anyone's interested!

Wasmtime GitHub notifications bot (Mar 16 2026 at 15:52):

alexcrichton added the wasmtime:c-api label to Issue #12783.

Wasmtime GitHub notifications bot (Mar 16 2026 at 15:55):

alexcrichton added the wasm-proposal:gc label to Issue #12783.

Wasmtime GitHub notifications bot (Mar 16 2026 at 20:47):

tolumide-ng commented on issue #12783:

Happy to pick this up, thank you :smile:

Wasmtime GitHub notifications bot (Mar 19 2026 at 23:03):

tolumide-ng commented on issue #12783:

Thank you @alexcrichton! I’m still getting familiar with the codebase, but I’ve opened a PR:https://github.com/bytecodealliance/wasmtime/pull/12805.
It seems wasmtime's gc enables properties that would otherwise have to be implemented manually when gc is disabled (e.g., RootScope). At the moment, I have enabled the gc feature by default while allowing downstream users to disable it, preserving backward compatibility. What do you think?

Wasmtime GitHub notifications bot (Apr 09 2026 at 21:15):

alexcrichton closed issue #12783:

In the c-api crate, the c-api specifies wasmtime as a dependency and explicitly enumerates its default features. Cargo permits overriding the features in a subdependency by explicitly passing the subdependency and a set of features, such as this:

[dependencies]
wasmtime = {version = "42.0.1", default-features = false, features = ['std', 'runtime']}
wasmtime-c-api-impl = {version = "42.0.1", features = ['cranelift']}

However, this is not able to _disable_ explicitly selected features of subdependencies (as default-features = false only applies to the features in the wasmtime crate's own Cargo.toml).

wasmtime's c-api crate already includes a feature to toggle gc, so the explicit inclusion of gc in the wasmtime's features is unnecessary. The fix would be to avoid specifying features for the wasmtime dependency in the c-api crate's Cargo.toml.

This change could be made backwards compatible by enabling the wasmtime c-api crate's gc feature by default, which would transitively enable wasmtime's gc feature in a way that could be disabled by consumers.

Related: https://github.com/proxy-wasm/proxy-wasm-cpp-host/pull/502#discussion_r2873328850

Last updated: Apr 12 2026 at 23:10 UTC