Stream: git-wasmtime

Topic: wasmtime / PR #13235 Fill out GC type reflection in the C...

Wasmtime GitHub notifications bot (Apr 30 2026 at 00:39):

alexcrichton opened PR #13235 from alexcrichton:c-api-reftypes to bytecodealliance:main:

This commit fills out APIs necessary to reflect on value types to get the full type hierarchy of WebAssembly. Currently types in the C API are primarily inherited from wasm.h which notably doesn't handle proposals such as simd or GC or typed function references. This puts us in a bit of an awkward position where much of our API relies on wasm.h, but there's obvious holes in wasm.h that would otherwise require modifications.

This commit takes the route of adding a parallel wasmtime_valtype_t definition fully tailored for Wasmtime's use case. Conversions are then provided between wasmtime_valtype_t and wasm_valtype_t. The Wasmtime version notably has a different representation which enables, for example, constructing primitive types without function calls.

This then fills out the corresponding C++ APIs and fills gaps in the preexisting types. For example FieldType is much different from before and now follows C++ idioms and semantics. Additionally it now has the ability to express the full breadth of all wasm types in fields and they can both be constructed and read.

This is all necessary for some implementation work to fill out the GC proposal in the wasmtime-py bindings where the lack of type information was otherwise leading to a pretty awkward API relative to the rest of the package.

<!--
Please make sure you include the following information:

• If this work has been discussed elsewhere, please include a link to that
  conversation. If it was discussed in an issue, just mention "issue #...".

• Explain why this change is needed. If the details are in an issue already,
  this can be brief.

Our development process is documented in the Wasmtime book:
https://docs.wasmtime.dev/contributing-development-process.html

Please ensure all communication follows the code of conduct:
https://github.com/bytecodealliance/wasmtime/blob/main/CODE_OF_CONDUCT.md
-->

Wasmtime GitHub notifications bot (Apr 30 2026 at 00:39):

alexcrichton requested fitzgen for a review on PR #13235.

Wasmtime GitHub notifications bot (Apr 30 2026 at 00:39):

alexcrichton requested wasmtime-core-reviewers for a review on PR #13235.

Wasmtime GitHub notifications bot (Apr 30 2026 at 03:59):

github-actions[bot] added the label wasmtime:c-api on PR #13235.

Wasmtime GitHub notifications bot (Apr 30 2026 at 14:12):

alexcrichton updated PR #13235.

Wasmtime GitHub notifications bot (Apr 30 2026 at 14:17):

alexcrichton updated PR #13235.

Wasmtime GitHub notifications bot (Apr 30 2026 at 14:18):

alexcrichton updated PR #13235.

Wasmtime GitHub notifications bot (May 01 2026 at 18:41):

:thumbs_up: fitzgen submitted PR review:

LGTM!

Wasmtime GitHub notifications bot (May 01 2026 at 18:41):

fitzgen added PR #13235 Fill out GC type reflection in the C API to the merge queue.

Wasmtime GitHub notifications bot (May 01 2026 at 19:07):

github-merge-queue[bot] removed PR #13235 Fill out GC type reflection in the C API from the merge queue.

Wasmtime GitHub notifications bot (May 01 2026 at 19:35):

alexcrichton updated PR #13235.

Wasmtime GitHub notifications bot (May 01 2026 at 19:35):

alexcrichton has enabled auto merge for PR #13235.

Wasmtime GitHub notifications bot (May 01 2026 at 19:52):

alexcrichton added PR #13235 Fill out GC type reflection in the C API to the merge queue.

Wasmtime GitHub notifications bot (May 01 2026 at 20:16):

github-merge-queue[bot] removed PR #13235 Fill out GC type reflection in the C API from the merge queue.

Wasmtime GitHub notifications bot (May 01 2026 at 22:53):

alexcrichton added PR #13235 Fill out GC type reflection in the C API to the merge queue.

Wasmtime GitHub notifications bot (May 01 2026 at 23:24):

:check: alexcrichton merged PR #13235.

Wasmtime GitHub notifications bot (May 01 2026 at 23:24):

alexcrichton removed PR #13235 Fill out GC type reflection in the C API from the merge queue.

Wasmtime GitHub notifications bot (May 28 2026 at 22:17):

martindevans commented on PR #13235:

This PR seems to have broken support for v128 in wasm_valtype_kind in release v45.

See https://github.com/bytecodealliance/wasmtime/blame/b333e5c207372a6f85b579fd43d508ccb6372ab3/crates/c-api/src/types/val.rs#L41. Is that intentional?

Wasmtime GitHub notifications bot (May 28 2026 at 22:31):

alexcrichton commented on PR #13235:

It was intentional, yes, because that was attempting to implement behavior that wasm.h doesn't support and if/when wasm.h eventually supports it, then it wasn't guaranteed to be compatible. Are you able to switch over to using wasmtime/types/val.h instead?

Wasmtime GitHub notifications bot (May 28 2026 at 22:48):

martindevans commented on PR #13235:

Thanks for the pointer to val.h, I'll have a look at it. This is for wasmtime-dotnet, so we should be able to wrap that instead and handle the changes internally.

Last updated: Jun 01 2026 at 09:49 UTC