feat: serialize RegExp objects over RPC

[dimitropoulos]

Adds by-value serialization for RegExp, aligning with Cloudflare Workers RPC structured-clonable type support.

Wire format: ["regexp", source, flags] (flags is always present, empty string when none).

From what I can tell, capnweb-validate already supports RegExp.

Based on the RegExp portion of the prior work in #99 (credit to @lmaccherone).

Closes #222.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4ec4f99

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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capnweb	Minor

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npm i https://pkg.pr.new/cloudflare/capnweb@225

commit: 4ec4f99

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

Adds by-value ["regexp", source, flags] serialization for RegExp, mirroring the existing Date handling.

Issue (high severity): RegExp round-trip is broken at the structuredClonable encoding level.

The Devaluator passes a native RegExp through unencoded when encodingLevel === "structuredClonable" (src/serialize.ts:340-341), exactly like Date (src/serialize.ts:331-332). But the Evaluator's structuredClonable passthrough (src/serialize.ts:818-822) only accepts raw Date and bigint values:

if (this.encodingLevel === "structuredClonable") {
  if (value instanceof Date || typeof value === "bigint") {
    return value;
  }
}

A raw RegExp is not an Array, so it never reaches the case "regexp" tuple decoder you added. Instead it falls through to the generic value instanceof Object branch (src/serialize.ts:1248), which iterates enumerable own properties and returns a plain object. Since RegExp has no enumerable own properties, an incoming RegExp at this level is silently corrupted into {} — the value is lost, not round-tripped.

This is exactly the path the PR targets ("aligning with Cloudflare Workers RPC structured-clonable type support"), and it isn't covered by tests: SERIALIZE_TEST_CASES only exercises the default serialize/deserialize (tuple) path, never structuredClonable.

Fix: mirror Date in the Evaluator passthrough at src/serialize.ts:819 (that unchanged line is outside this diff, so I can't attach the suggestion directly there):

if (value instanceof Date || value instanceof RegExp || typeof value === "bigint") {
  return value;
}

Also please add a structuredClonable-level round-trip test for RegExp so this path is covered.

Minor note: flags normalizes flag order (re.flags is sorted), so /x/mi round-trips as "im". That's harmless (equivalent semantics) and worth a mention only if strict flag-string preservation matters.

[ask-bonk]

This tuple decoder is only reached at non-structuredClonable levels. At structuredClonable level the value arrives as a raw RegExp (emitted by the Devaluator at line 340-341) and never becomes an Array, so it bypasses this case and is mangled into {} by the generic object path (line 1248). The corresponding fix is in the passthrough block at line 819:

if (value instanceof Date || value instanceof RegExp || typeof value === "bigint") {
  return value;
}

[ask-bonk]

Review posted successfully to PR #225.

I reviewed PR #225 (feat: serialize RegExp objects over RPC) and found one high-severity issue: the RegExp round-trip is broken at the structuredClonable encoding level. The Devaluator emits a raw RegExp there (mirroring Date), but the Evaluator's passthrough only whitelists Date and bigint, so an incoming RegExp gets mangled into an empty plain object {}. This is the exact path the PR aims to support (Cloudflare Workers RPC alignment) and is untested. I posted the review with a concrete fix and a request to add a structuredClonable-level round-trip test.

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[Copilot]

Pull request overview

Adds first-class RPC support for RegExp values, matching Cloudflare Workers’ structured-clonable type support and documenting the new wire encoding.

Changes:

• Introduces a new regexp RPC kind and corresponding (de)serialization logic using ["regexp", source, flags].
• Extends core payload handling to treat RegExp as an immutable/pass-by-value type in relevant traversal/copy/dispose paths.
• Updates docs (README + protocol) and adds round-trip tests for RegExp.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/serialize.ts	Adds RegExp tuple encoding/decoding and structured-clonable passthrough handling.
src/core.ts	Adds regexp to RPC type classification and payload traversal/copy/dispose switch cases.
README.md	Moves RegExp into the supported pass-by-value types list.
protocol.md	Documents the ["regexp", source, flags] wire format with an example.
.changeset/serialize-regexp.md	Declares a minor release for the new serialization capability.
tests/index.test.ts	Adds serialize/deserialize round-trip cases for RegExp.

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