feat(wit): add map type support #2356

yordis · 2025-10-17T18:56:55Z

alexcrichton · 2025-10-20T15:06:05Z

Thanks for this! Are you looking to get this merged ASAP? Or is this more of a proof-of-concept to support the development of the PR on the spec itself? If you're looking to get this merged sooner-rather-than-later, do you have plans to work on other parts of the stack such as wit-bindgen or Wasmtime?

yordis · 2025-10-20T17:31:11Z

@alexcrichton no rush at all in my end. I want to learn how to do the whole thing if possible if that is ok with you

yordis · 2025-10-21T17:58:54Z

Note for self: 0x63 why is that typed in so many places instead of having a enum somewhere?

crates/wit-component/src/encoding.rs

crates/wit-parser/src/ast/resolve.rs

alexcrichton

Ok looked over things, and thanks for this!

In terms of implementing this, adding a new type is a relatively major endeavor that takes awhile as there are a lot of integration points. Given that we'll want to make sure that this work is properly "gated" from external users to avoid, in theory, accidentally hitting unimplemented parts of the type system. The primary way this is done is via WasmFeatures in the wasmparser crate. What I'd recommend is adding a new cm_map feature similar to cm_fixed_size_lists. Effectively you'll want to add a bunch of tests/checks/etc in the same manner as fixed-size-lists, also an unstable feature at this time.

Additionally you'll want to add tests in tests/cli/component-model/*.wast for this new type as well. You should be able to find tests for fixed-size-lists around there and you can structure tests in a similar way.

Other than that though I think this would be reasonable to land. After landing here would come integration work into wasmtime/wit-bindgen/etc.

crates/wasmparser/src/validator/component_types.rs

crates/wit-component/src/encoding.rs

crates/wit-dylib/ffi/src/ffi.rs

crates/wit-parser/src/ast/resolve.rs

alexcrichton

Looking good, thanks! The remaining things I can think of are:

This needs a new feature gate in wasmparser's validation to ensure that this isn't accidentally usable-by-default.
This needs *.wast tests for the component-model side of things to ensure that the type works in the text format, validation, etc. There should also be tests ensuring that if the feature gate is disabled that usage of the type is an error (you can copy fixed-size-list tests for example)
Tests are currently not passing in CI, so that'll need to be green

alexcrichton · 2025-12-19T15:47:57Z

@yordis it looks like the feature gating still isn't implemented?

yordis · 2025-12-19T17:31:44Z

@alexcrichton 🤦🏻 sorry ... I completely forgot focusing on making CI to pass again resolving the comments ... let me work on that

yordis · 2025-12-19T18:42:05Z

cargo fmt
Error writing files: failed to resolve mod bindings: /Users/yordisstudio/Developer/github.com/bytecodealliance/wasm-tools/playground/component/src/bindings.rs does not exist

@alexcrichton when I ran cargo fmt it seems that there is a missing file here, what is reason for that file to be missing from the code base? Or rather, at the very least be added to a .gitignore so I can keep a dummy file to make the formatter to work

alexcrichton · 2025-12-19T21:45:19Z

Sorry I'm not sure what you're referring to? If you run find . -name '*.rs' | xargs rustfmt --check --edition 2021 like CI does, does that fix things? (no CI is currently being run due to a merge conflict)

Signed-off-by: Yordis Prieto <yordis.prieto@gmail.com>

… map type

…List types

…ib smoke test output

Map keys must be primitive types only. Add validation to reject non-primitive types (floats, user-defined types, etc.) as map keys.

…ature

…ent model Signed-off-by: Yordis Prieto <yordis.prieto@gmail.com>

…d snapshots

yordis · 2025-12-19T23:08:50Z

Sorry I'm not sure what you're referring to? If you run find . -name '*.rs' | xargs rustfmt --check --edition 2021 like CI does, does that fix things?

Yeah, just wondering why the cargo fmt by itself wouldn't work here, no biggy

crates/wit-component/tests/interfaces.rs

alexcrichton

Thanks!

crates/wit-component/tests/interfaces.rs

alexcrichton · 2025-12-22T16:40:36Z

crates/wasmparser/src/features.rs

+        ///
+        /// Corresponds to the 🗺️ character in
+        /// <https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md>.
+        pub cm_map: CM_MAP(1 << 37) = false;


I think the 37 here conflicts with compact_imports below now. I think it's reasonable to leave this adjacent to cm_gc, but feel free to renumber the below bits to ensure the biggest number is last

It scares me that my tests passed 😭 I do not like things no breaking with these type of changes.

Could this use a enum thou?

…t documentation

yordis · 2025-12-22T17:56:57Z

crates/wasmparser/src/features.rs

+        ///
+        /// Corresponds to the 🗺️ character in
+        /// <https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md>.
+        pub cm_map: CM_MAP(1 << 38) = false;


I rather keep it based on the flag value than grouping things ... I think that caused the issue to begin with

yordis force-pushed the yordis/add-map-support branch 4 times, most recently from cd02439 to 2487714 Compare October 21, 2025 02:11

yordis commented Oct 21, 2025

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yordis marked this pull request as ready for review October 21, 2025 19:39

yordis requested a review from a team as a code owner October 21, 2025 19:39

yordis requested review from pchickey and removed request for a team October 21, 2025 19:39

alexcrichton requested review from alexcrichton and removed request for pchickey October 21, 2025 21:51

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yordis requested a review from alexcrichton November 21, 2025 19:56

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yordis force-pushed the yordis/add-map-support branch 2 times, most recently from 1e65742 to 2ea4fec Compare December 3, 2025 21:11

yordis force-pushed the yordis/add-map-support branch from 2ea4fec to f1a8786 Compare December 15, 2025 00:32

yordis requested a review from alexcrichton December 15, 2025 08:36

yordis force-pushed the yordis/add-map-support branch 2 times, most recently from 8698f34 to 51b1558 Compare December 19, 2025 18:48

feat(wit): add map type support

715a7ac

Signed-off-by: Yordis Prieto <yordis.prieto@gmail.com>

yordis added 11 commits December 19, 2025 18:03

refactor(wit): remove key type validation from map resolution

3cfde01

refactor(wit): rename LIST to NEEDS_MEMORY in TypeContents for clarity

d4ca0ea

feat(wasmparser): add error handling for unimplemented GC lowering of…

f39d9c8

… map type

refactor(wit): revert map type support from the dylib

bde4b84

refactor(wasmparser): clean up match statement for List and FixedSize…

72ea306

…List types

fix(wit-dylib): adjust memory size and update function indices in dyl…

e6bbddd

…ib smoke test output

fix(wit-parser): add validation for map key types

37dc4b9

Map keys must be primitive types only. Add validation to reject non-primitive types (floats, user-defined types, etc.) as map keys.

chore: format code

00afdb1

feat(wasmparser): add feature flag support for component model map fe…

ee6b3d7

…ature

feat(wast): add support for map custom keyword and encoding in compon…

2a24e34

…ent model Signed-off-by: Yordis Prieto <yordis.prieto@gmail.com>

fix(tests): update WAST files to use imports for map functions and ad…

4f3e386

…d snapshots

yordis force-pushed the yordis/add-map-support branch from f70170f to 4f3e386 Compare December 19, 2025 23:07

yordis commented Dec 19, 2025

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alexcrichton approved these changes Dec 22, 2025

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fix(wasmparser): update cm_map feature flag to new encoding and adjus…

23f1581

…t documentation

yordis commented Dec 22, 2025

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fix(tests): update error message for unknown features in validation test

fe58298

alexcrichton approved these changes Dec 22, 2025

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alexcrichton added this pull request to the merge queue Dec 22, 2025

Merged via the queue into bytecodealliance:main with commit 165430b Dec 22, 2025
34 checks passed

yordis deleted the yordis/add-map-support branch December 22, 2025 19:09

yordis mentioned this pull request Dec 23, 2025

Add support for map type bytecodealliance/wasmtime#12216

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feat(wit): add map type support #2356

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