Wasmtime GitHub notifications bot (May 29 2026 at 22:05): Wasmtime GitHub notifications bot (May 29 2026 at 22:05):alexcrichton opened PR #13513 from alexcrichton:finish-implements to bytecodealliance:main:
This commit is the final step in finishing up the bindings generation story for
bindgen!w.r.t. the(implement ...)component model feature. Namelybindgen!now has the optionnamed_imports: { ... }which generates a new top-levelnamed_importsmodule with nested modules within it. These nested modules are similar to the default-generated ones except that they additionally take an extra "id" parameter in all trait methods. Theadd_to_linkerfunction additionally takes both a&Componentand alookupfunction.Putting all this together the expected flow is:
Host decide they want to accept any number of
import a: b:c/d;from components at runtime. Bindings are generated withnamed_imports: { ... }in thebindgen!invocation.Hosts switch from linker-per-engine to instead using a linker-per-component. After the typical population of items within the
Linkernext the host uses thenamed_imports::b::c::d::add_to_linker, for example. Here the host performs lookup from whatever string was found in the component to an ID key that the host knows about. Upon success this key will be closed over in alladd_to_linkerfunctions. Upon failure theadd_to_linkerclosure fails.This per-component linker is used to instantiate and create instances as usual. At runtime when a named import is invoked the closed-over ID is passed to the trait implementation as a parameter. Hosts can thus disambiguate through which interface the component made a call through.
Some light tests are added throughout this showcasing the various capabilities. This notably added a new
ComponentExtern::is_implementsmethod to peform semver-matching automatically so hosts can generate bindings with one version and still acceptimplementswith other slightly different but compatible versions.<!--
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Wasmtime GitHub notifications bot (May 29 2026 at 22:05):alexcrichton requested pchickey for a review on PR #13513.
Wasmtime GitHub notifications bot (May 29 2026 at 22:05):alexcrichton requested wasmtime-core-reviewers for a review on PR #13513.
Wasmtime GitHub notifications bot (May 29 2026 at 23:05):github-actions[bot] added the label wasmtime:api on PR #13513.
Wasmtime GitHub notifications bot (May 29 2026 at 23:16):tschneidereit commented on PR #13513:
- Hosts switch from linker-per-engine to instead using a linker-per-component.
One thing I didn't think about when we discussed this yesterday: how much overhead does this introduce for hosts with large numbers of components loaded? (I'm not sure how much of a real alternative to this design there is, but I'd at least like to understand the costs a bit better.)
Wasmtime GitHub notifications bot (Jun 01 2026 at 14:12):alexcrichton commented on PR #13513:
I always forget to correct that as well, but what hosts are doing right now is actually a linker-per-engine plus an instance-pre-per-component. This PR doesn't change the latter, still an instance-pre-per-component, and the main difference is that when creating an instance-pre-per-component the host will likely
.clone()the per-engine linker, add more items, then create the instance pre, then discard the temporary linker. I wouldn't expect any negligible resource increase or decrease from this.
Wasmtime GitHub notifications bot (Jun 01 2026 at 14:50):tschneidereit commented on PR #13513:
I wouldn't expect any negligible resource increase or decrease from this.
Assuming you mean
s/negligible/non-negligible/: great! :)
Wasmtime GitHub notifications bot (Jun 01 2026 at 15:01):alexcrichton commented on PR #13513:
Oops, yes!
Wasmtime GitHub notifications bot (Jun 03 2026 at 14:47):alexcrichton updated PR #13513.
Wasmtime GitHub notifications bot (Jun 03 2026 at 16:34)::thumbs_up: pchickey submitted PR review.
Wasmtime GitHub notifications bot (Jun 03 2026 at 16:41):alexcrichton added PR #13513 Finish bindings generation for (implements ..) to the merge queue
Wasmtime GitHub notifications bot (Jun 03 2026 at 17:06)::check: alexcrichton merged PR #13513.
Wasmtime GitHub notifications bot (Jun 03 2026 at 17:06):alexcrichton removed PR #13513 Finish bindings generation for (implements ..) from the merge queue
Last updated: Jul 29 2026 at 05:03 UTC