Stream: git-wasmtime

Topic: wasmtime / PR #13671 Enable reflecting most `Config` valu...

Wasmtime GitHub notifications bot (Jun 16 2026 at 20:53):

alexcrichton opened PR #13671 from alexcrichton:serialize-engine to bytecodealliance:main:

This commit adds a number of pieces of plumbing/etc where the end goal is to be able to reflect upon the configuration values from an Engine. The pieces added here are:

• Many new get_* methods now exist on Engine to read out the configuration values specified. These are intended to not return an Option<T> in most cases to accurately reflect Wasmtime's defaults and configuration.

• The wasmtime-cli-flags is now feature'd to have a separate clap, serde, and toml feature.

• The wasmtime-cli-flags crate structures now sport a Serialize implementation to go along with their Deserialize implementation.

• A new wasmtime_cli_flags::CommonOptions::from_engine method was added to extract configuration from an Engine.

The intent here is that all raw getters are present on Engine itself, not Config. This is an intentional decision as Config is a part-way piece of configuration which doesn't necessarily have all defaults/etc loaded to determine the true final configuration options. An Engine, however, is a finalized piece of configuration which has a finalized Tunables, for example.

Additionally Engine has accessors based on Config names, but it's also easy to forget to add these over time. Additionally everything's not in a nicely serializable format, but that's what CommonOptions packages up nicely. The from_engine method bridges this gap by connecting all Engine options to an exhaustive construction of all CLI options. This means that if we forget to add one in the future we'll at least get a compiler error to alert us.

The overall goal with this is to assist with embeddings updating wasmtime over time. It should now be much easier to serialize Wasmtime's default configuration to a file and persist that across major Wasmtime versions. This enables embeddings to configure modules uniformly over time and have at least mostly similar settings across versions of Wasmtime.

I'll note as well that from_engine is not exhaustive. There are configuration options that fundamentally can't be captured in a serializable format, such a MemoryCreator (a trait object). This is documented on from_engine where it's intended to represent a major subset of configuration but not exhaustive. This is suitable for applications, though, which exclusively derive a Config from CommonOptions (or similar) where it can be understood that everything is still serializable there.

<!--
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 (Jun 16 2026 at 20:53):

alexcrichton requested wasmtime-core-reviewers for a review on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 20:53):

alexcrichton requested pchickey for a review on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 20:53):

alexcrichton requested fitzgen for a review on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 20:53):

alexcrichton requested wasmtime-default-reviewers for a review on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 21:01):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 21:13):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 21:25):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 21:25):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 22:23):

github-actions[bot] added the label wasmtime:config on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 22:23):

github-actions[bot] added the label wasmtime:api on PR #13671.

Wasmtime GitHub notifications bot (Jun 16 2026 at 22:24):

github-actions[bot] commented on PR #13671:

Label Messager: wasmtime:config

It looks like you are changing Wasmtime's configuration options. Make sure to
complete this check list:

• [ ] If you added a new Config method, you wrote extensive documentation for
  it.

  <details>

  Our documentation should be of the following form:

  ```text
  Short, simple summary sentence.

  More details. These details can be multiple paragraphs. There should be
  information about not just the method, but its parameters and results as
  well.

  Is this method fallible? If so, when can it return an error?

  Can this method panic? If so, when does it panic?

  Example

  Optional example here.
  ```

  </details>

• [ ] If you added a new Config method, or modified an existing one, you
  ensured that this configuration is exercised by the fuzz targets.

  <details>

  For example, if you expose a new strategy for allocating the next instance
  slot inside the pooling allocator, you should ensure that at least one of our
  fuzz targets exercises that new strategy.

  Often, all that is required of you is to ensure that there is a knob for this
  configuration option in [wasmtime_fuzzing::Config][fuzzing-config] (or one
  of its nested structs).

  Rarely, this may require authoring a new fuzz target to specifically test this
  configuration. See [our docs on fuzzing][fuzzing-docs] for more details.

  </details>

• [ ] If you are enabling a configuration option by default, make sure that it
  has been fuzzed for at least two weeks before turning it on by default.

[fuzzing-config]: https://github.com/bytecodealliance/wasmtime/blob/ca0e8d0a1d8cefc0496dba2f77a670571d8fdcab/crates/fuzzing/src/generators.rs#L182-L194
[fuzzing-docs]: https://docs.wasmtime.dev/contributing-fuzzing.html

---

<details>

To modify this label's message, edit the <code>.github/label-messager/wasmtime-config.md</code> file.

To add new label messages or remove existing label messages, edit the
<code>.github/label-messager.json</code> configuration file.

Learn more.

</details>

Wasmtime GitHub notifications bot (Jun 17 2026 at 01:29):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 17 2026 at 14:39):

alexcrichton updated PR #13671.

Wasmtime GitHub notifications bot (Jun 17 2026 at 18:23):

:thumbs_up: fitzgen submitted PR review.

Wasmtime GitHub notifications bot (Jun 17 2026 at 18:23):

:speech_balloon: fitzgen created PR review comment:

Nice to remove the vm config type

Wasmtime GitHub notifications bot (Jun 17 2026 at 18:26):

alexcrichton added PR #13671 Enable reflecting most Config values through Engine to the merge queue

Wasmtime GitHub notifications bot (Jun 17 2026 at 19:41):

:check: alexcrichton merged PR #13671.

Wasmtime GitHub notifications bot (Jun 17 2026 at 19:41):

alexcrichton removed PR #13671 Enable reflecting most Config values through Engine from the merge queue

Last updated: Jul 29 2026 at 05:03 UTC