From 7d5befa9c00bd214a933223816d50792d3ede475 Mon Sep 17 00:00:00 2001
From: greymoth-jp <246701683+greymoth-jp@users.noreply.github.com>
Date: Mon, 29 Jun 2026 17:16:56 +0900
Subject: [PATCH] fix: support RegExp flags added after es2017 in clone and
 patch

cloneRegExp and the trivial patch filter both re-parse the output of
RegExp.prototype.toString() with a `[gimyu]` flag character class. That
class predates the `s` (es2018), `d` (es2022) and `v` (es2024) flags, so
clone() throws "Invalid RegExp" on any RegExp that uses one of them, and
diffing then patching such a RegExp silently turns it back into a string.
Widen both classes to `[dgimsuvy]` so every currently valid flag is kept.
---
 packages/jsondiffpatch/src/clone.ts               |  2 +-
 packages/jsondiffpatch/src/filters/trivial.ts     |  2 +-
 packages/jsondiffpatch/test/examples/diffpatch.ts | 12 ++++++++++++
 packages/jsondiffpatch/test/index.spec.ts         | 10 ++++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/packages/jsondiffpatch/src/clone.ts b/packages/jsondiffpatch/src/clone.ts
index cf6d3310..004b1bc1 100644
--- a/packages/jsondiffpatch/src/clone.ts
+++ b/packages/jsondiffpatch/src/clone.ts
@@ -1,5 +1,5 @@
 function cloneRegExp(re: RegExp) {
-	const regexMatch = /^\/(.*)\/([gimyu]*)$/.exec(re.toString());
+	const regexMatch = /^\/(.*)\/([dgimsuvy]*)$/.exec(re.toString());
 	if (!regexMatch) {
 		throw new Error("Invalid RegExp");
 	}
diff --git a/packages/jsondiffpatch/src/filters/trivial.ts b/packages/jsondiffpatch/src/filters/trivial.ts
index 47041c0e..34f576a6 100644
--- a/packages/jsondiffpatch/src/filters/trivial.ts
+++ b/packages/jsondiffpatch/src/filters/trivial.ts
@@ -88,7 +88,7 @@ export const patchFilter: Filter<PatchContext> =
 		}
 		if (nonNestedDelta.length === 2) {
 			if (context.left instanceof RegExp) {
-				const regexArgs = /^\/(.*)\/([gimyu]+)$/.exec(
+				const regexArgs = /^\/(.*)\/([dgimsuvy]+)$/.exec(
 					nonNestedDelta[1] as string,
 				);
 				if (regexArgs?.[1]) {
diff --git a/packages/jsondiffpatch/test/examples/diffpatch.ts b/packages/jsondiffpatch/test/examples/diffpatch.ts
index 1e5e4211..317ebe6f 100644
--- a/packages/jsondiffpatch/test/examples/diffpatch.ts
+++ b/packages/jsondiffpatch/test/examples/diffpatch.ts
@@ -17,6 +17,11 @@ type ExampleGroup = Example[];
 
 const exampleDate = () => new Date(2020, 10, 30, 15, 10, 3);
 
+// Built via the constructor rather than a `/…/s` literal so these compile under
+// the repo's es6 target (the `s` flag postdates es6 and a literal would error).
+const regExpWithFlags = (source: string, flags: string) =>
+	new RegExp(source, flags);
+
 const atomicValues: ExampleGroup = [
 	// undefined
 	{
@@ -464,6 +469,13 @@ const atomicValues: ExampleGroup = [
 		delta: ["/regex/g", "/another regex/gi"],
 		reverse: ["/another regex/gi", "/regex/g"],
 	},
+	{
+		name: "RegExp -> RegExp (dotAll flag)",
+		left: regExpWithFlags("regex", "s"),
+		right: regExpWithFlags("another regex", "s"),
+		delta: ["/regex/s", "/another regex/s"],
+		reverse: ["/another regex/s", "/regex/s"],
+	},
 
 	// object
 	{
diff --git a/packages/jsondiffpatch/test/index.spec.ts b/packages/jsondiffpatch/test/index.spec.ts
index 48392288..aca5b8f1 100644
--- a/packages/jsondiffpatch/test/index.spec.ts
+++ b/packages/jsondiffpatch/test/index.spec.ts
@@ -137,6 +137,16 @@ describe("DiffPatcher", () => {
 				pattern: /expr/gim,
 			});
 		});
+		it("clones RegExp with flags added after es2017 (s, d, v)", () => {
+			// `s` (es2018), `d` (es2022) and `v` (es2024) all postdate the repo's
+			// es6 target, so build via the constructor with a non-literal flag
+			// (a `/…/s` literal would not compile).
+			for (const flag of ["s", "d", "v"]) {
+				const pattern = new RegExp("expr", flag);
+				const cloned = jsondiffpatch.clone({ pattern });
+				expect(cloned).toEqual({ pattern });
+			}
+		});
 	});
 
 	describe("using cloneDiffValues", () => {