Stream: git-wasmtime

Topic: wasmtime / PR #14927 Add a `map_type` option to `bindgen!...

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf opened PR #14927 from jrandolf:bindgen-map-type-option to bytecodealliance:main:

This builds on #14870, so only the last commit is new here.

This adds a map_type option to bindgen! to choose the Rust type used for WIT maps, such as map_type: std::collections::HashMap or map_type: indexmap::IndexMap. It mirrors the guest-side wit-bindgen option, including its BTreeMap default (see the discussion on #14837). BTreeMap is available without std, so the generated code no longer depends on the features Wasmtime is built with, which fixes #14830. It also makes additional_derives such as Hash and Ord work for records containing maps.

This changes the signatures generated for maps, which are only usable with the component model's map feature, which is off by default.

Closes #14830
Closes #14832

<details>
<summary>LLM summary of the changes</summary>

Option (component-macro/src/bindgen.rs, wit-bindgen)

• map_type takes a path to a type with <K, V> parameters, like wasmtime_crate takes a path. Without it, maps are BTreeMap, referenced through Wasmtime's __internal re-exports so it works from no_std crates.
• RustGenerator::map_type_path returns the path, and both places that print map types use it: named map types, and the map() helper for anonymous ones from #14838.
• A type alias works for a HashMap with a custom hasher. The path is used from within generated modules, so it should be absolute, for example crate::MyMap.

Docs

The bindgen! docs list map_type's options: BTreeMap (the default), std::collections::HashMap and indexmap::IndexMap.

Tests

• The map snapshots from #14834 are regenerated for the BTreeMap default. Only the type changes.
• component-macro/tests/codegen.rs checks that the default bindings compile with additional_derives: [Hash, PartialEq, Eq, PartialOrd, Ord] on a record containing a map, and that a custom-hasher alias works as map_type.

</details>

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf removed the review request for wasmtime-core-reviewers from PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf requested wasmtime-core-reviewers for a review on PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf requested dicej for a review on PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf removed the review request for wasmtime-default-reviewers from PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf requested wasmtime-default-reviewers for a review on PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 20:58):

jrandolf requested fitzgen for a review on PR #14927.

Wasmtime GitHub notifications bot (Oct 21 2026 at 23:45):

github-actions[bot] added the label wasmtime:api on PR #14927.

Wasmtime GitHub notifications bot (Oct 22 2026 at 19:41):

:thumbs_up: fitzgen submitted PR review:

Looks reasonable to me, thanks

Wasmtime GitHub notifications bot (Oct 22 2026 at 19:42):

fitzgen added PR #14927 Add a map_type option to bindgen!, defaulting to BTreeMap to the merge queue

Wasmtime GitHub notifications bot (Oct 22 2026 at 20:31):

fitzgen removed PR #14927 Add a map_type option to bindgen!, defaulting to BTreeMap from the merge queue

Wasmtime GitHub notifications bot (Oct 22 2026 at 20:31):

:check: fitzgen merged PR #14927.

Last updated: Oct 31 2026 at 23:03 UTC