Ignore inferred arity in case of %raw.

[cristianoc]

The inferred arity of raw JS code is actively used with %ffi, but it can produce unexpected results with %raw:

let foo: int => int = %raw(`function add(x, y=5){ return x + y }`)

Console.log(foo(2))

This PR tests turning off the use of inferred arity so that int => int above is just taken at face value.

[tsnobip]

@cristianoc this means inferred arity will be ignored even when there's no type signature, right? It's dangerous anyway since it doesn't reflect it in the types.
I guess you can still use %ffi if you want to type your js code. We should likely document %ffi by the way.

[Copilot]

Pull Request Overview

This PR disables the inferred arity for raw JavaScript code passed to %raw, ensuring that the provided type annotations (e.g. int => int) are respected rather than inferring parameters from the raw JS function.

• Updated tests to validate the behavior with raw JS code.
• Removed logic handling arity inference for %raw code in the compiler passes.
• Updated the CHANGELOG to document this bug fix.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/tests/src/raw_arity.res	Adds a test using %raw to confirm that arity inference is disabled.
tests/tests/src/raw_arity.mjs	Mirrors the Rescript test for raw JS code in JavaScript.
compiler/core/lam_pass_collect.ml	Removes the arity inference logic for %raw JS code in the lam pass collection.
compiler/core/lam_arity_analysis.ml	Removes the arity inference handling for %raw JS functions in arity analysis.
CHANGELOG.md	Documents the bug fix regarding raw JS arity inference.

Comments suppressed due to low confidence (2)

compiler/core/lam_pass_collect.ml:64

• Ensure that the removal of arity inference is paired with proper fallback handling for %raw usage, and consider adding a clarifying comment to explain why this case is now ignored.

    | Lprim {primitive = Psome | Psome_not_nest; args = [v]} ->

compiler/core/lam_arity_analysis.ml:69

• Confirm that dropping this case does not affect other related arity analyses, and add inline documentation linking this change to the PR rationale for future maintainability.

    with

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