Stream: git-wasmtime

Topic: wasmtime / PR #12089 Add `Config::without_compiler`

Wasmtime GitHub notifications bot (Nov 25 2025 at 19:22):

fitzgen opened PR #12089 from fitzgen:config-without-compiler to bytecodealliance:main:

This provides us an allocation-free path for constructing a Config.

Why not rely on builds when cfg(not(any(feature = "cranelift", feature = "winch")))? Because we need to test our various OOM-handling and allocation-free code paths in this workspace, and without some way to create a config without a compiler otherwise, cargo's feature resolver will enable those features in the workspace, enabling the compiler in the config, but we don't intend to make compiler configurations handle OOM.

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Wasmtime GitHub notifications bot (Nov 25 2025 at 19:22):

fitzgen requested alexcrichton for a review on PR #12089.

Wasmtime GitHub notifications bot (Nov 25 2025 at 19:22):

fitzgen requested wasmtime-core-reviewers for a review on PR #12089.

Wasmtime GitHub notifications bot (Nov 25 2025 at 19:22):

fitzgen requested wasmtime-fuzz-reviewers for a review on PR #12089.

Wasmtime GitHub notifications bot (Nov 25 2025 at 20:16):

alexcrichton submitted PR review:

Bikeshed on this: WDYT about:

• Leave Config::new as the only constructor
• Add a Config::enable_compiler(&mut self, bool) method
• Defer the default Cranelift configuration to happening in build_compiler

That way we keep just a single constructor and this, in theory, would still compose well with other options. (and try_compiler would still remain)

Wasmtime GitHub notifications bot (Nov 25 2025 at 21:45):

github-actions[bot] commented on PR #12089:

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This issue or pull request has been labeled: "fuzzing", "wasmtime:api", "wasmtime:config"

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Wasmtime GitHub notifications bot (Nov 25 2025 at 22:46):

github-actions[bot] commented on PR #12089:

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

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Wasmtime GitHub notifications bot (Dec 01 2025 at 22:11):

fitzgen commented on PR #12089:

Defer the default Cranelift configuration to happening in build_compiler

This seems kind of difficult since we don't really know if our defaults were overridden with other Config::cranelift_flag_{enable,set} calls or whatever unless we start doing more introspection on the given flags and duplicating state between Config and the compiler, which feels pretty nasty.

Wasmtime GitHub notifications bot (Dec 01 2025 at 22:15):

fitzgen updated PR #12089.

Wasmtime GitHub notifications bot (Dec 01 2025 at 22:31):

alexcrichton commented on PR #12089:

Could the defaults be pushed into the Cranelift/Winch compiler builder than? Adding a new constructor is a really heavy hammer I'd prefer to avoid, so I'd ideally like to push pretty hard on solving the problems of using the existing constructor

Wasmtime GitHub notifications bot (Dec 01 2025 at 22:31):

alexcrichton edited a comment on PR #12089:

Could the defaults be pushed into the Cranelift/Winch compiler builder then? Adding a new constructor is a really heavy hammer I'd prefer to avoid, so I'd ideally like to push pretty hard on solving the problems of using the existing constructor

Wasmtime GitHub notifications bot (Dec 02 2025 at 19:26):

fitzgen requested cfallin for a review on PR #12089.

Wasmtime GitHub notifications bot (Dec 02 2025 at 19:26):

fitzgen updated PR #12089.

Wasmtime GitHub notifications bot (Dec 02 2025 at 19:26):

fitzgen requested wasmtime-compiler-reviewers for a review on PR #12089.

Wasmtime GitHub notifications bot (Dec 02 2025 at 19:26):

fitzgen commented on PR #12089:

Could the defaults be pushed into the Cranelift/Winch compiler builder then? Adding a new constructor is a really heavy hammer I'd prefer to avoid, so I'd ideally like to push pretty hard on solving the problems of using the existing constructor

Done, want to take another look?

Wasmtime GitHub notifications bot (Dec 02 2025 at 20:22):

alexcrichton submitted PR review.

Wasmtime GitHub notifications bot (Dec 02 2025 at 20:22):

alexcrichton commented on PR #12089:

Thanks!

Wasmtime GitHub notifications bot (Dec 03 2025 at 00:13):

alexcrichton merged PR #12089.

Last updated: Dec 06 2025 at 07:03 UTC