NaN Coercion

.changeset/humble-lizards-judge.md

@@ -6,4 +6,4 @@
 
 * **BREAKING**: The `boolean` keyword has been removed. Universal boolean coercion is now handled by the `arkenv` package.
 * **BREAKING**: The `port` keyword has been changed from a `string -> number` morph to a pure `number` refinement. Numeric coercion is now handled centrally.
-* Added `maybeParsedNumber` and `maybeParsedBoolean` internal morphs to support central coercion.
+* Added `maybeParsedNumber` and `maybeParsedBoolean` internal morphs to support central coercion (including specific "NaN" support).

packages/arkenv/src/utils/coerce.test.ts

@@ -191,4 +191,26 @@ describe("coerce", () => {
 			VITE_MY_NUMBER_MANUAL: 456,
 		});
 	});
+
+	it("should coerce 'NaN' string to NaN number", () => {
+		const schema = type({
+			VAL: "number.NaN",
+		});
+		const coercedSchema = coerce(schema);
+		const result = coercedSchema({ VAL: "NaN" });
+		expect(result).not.toBeInstanceOf(ArkErrors);
+		if (result instanceof ArkErrors) return;
+		expect(result.VAL).toBeNaN();
+	});
+
+	it("should fail to validate 'NaN' string with standard 'number' keyword", () => {
+		const schema = type({
+			VAL: "number",
+		});
+		// Coercion happens ("NaN" -> NaN), but "number" checks and rejects NaN
+		const coercedSchema = coerce(schema);
+		const result = coercedSchema({ VAL: "NaN" });
+		expect(result).toBeInstanceOf(ArkErrors);
+		expect(result.toString()).toContain("VAL must be a number (was NaN)");
+	});
 });

packages/arkenv/src/utils/coerce.ts

@@ -114,7 +114,7 @@ const applyCoercion = (data: unknown, targets: CoercionTarget[]) => {
 		// If root data needs coercion (e.g. root schema is number/boolean), handle it
 		if (targets.some((t) => t.path.length === 0)) {
 			const asNumber = maybeParsedNumber(data);
-			if (typeof asNumber === "number" && !Number.isNaN(asNumber)) {
+			if (typeof asNumber === "number") {
 				return asNumber;
 			}
 			return maybeParsedBoolean(data);
@@ -146,7 +146,7 @@ const applyCoercion = (data: unknown, targets: CoercionTarget[]) => {
 					for (let i = 0; i < current.length; i++) {
 						const original = current[i];
 						const asNumber = maybeParsedNumber(original);
-						if (typeof asNumber === "number" && !Number.isNaN(asNumber)) {
+						if (typeof asNumber === "number") {
 							current[i] = asNumber;
 						} else {
 							current[i] = maybeParsedBoolean(original);
@@ -165,16 +165,16 @@ const applyCoercion = (data: unknown, targets: CoercionTarget[]) => {
 					for (let i = 0; i < original.length; i++) {
 						const item = original[i];
 						const asNumber = maybeParsedNumber(item);
-						if (typeof asNumber === "number" && !Number.isNaN(asNumber)) {
+						if (typeof asNumber === "number") {
 							original[i] = asNumber;
 						} else {
 							original[i] = maybeParsedBoolean(item);
 						}
 					}
 				} else {
 					const asNumber = maybeParsedNumber(original);
-					// If numeric parsing didn't change type (still string) or is NaN/invalid, try boolean
-					if (typeof asNumber === "number" && !Number.isNaN(asNumber)) {
+					// If numeric parsing didn't produce a number, try boolean coercion
+					if (typeof asNumber === "number") {
 						record[lastKey] = asNumber;
 					} else {
 						record[lastKey] = maybeParsedBoolean(original);

packages/internal/keywords/src/index.ts

@@ -11,10 +11,12 @@ import { type } from "arktype";
  */
 export const maybeParsedNumber = type("unknown").pipe((s) => {
 	if (typeof s === "number") return s;
-	if (typeof s !== "string" || s.trim() === "") return s;
-	const n = Number(s);
-	if (Number.isNaN(n) && s !== "NaN") return s;
-	return n;
+	if (typeof s !== "string") return s;
+	const trimmed = s.trim();
+	if (trimmed === "") return s;
+	if (trimmed === "NaN") return Number.NaN;
+	const n = Number(trimmed);
+	return Number.isNaN(n) ? s : n;
 });
 
 /**