fix(schema): prevent crash validating unions of object arrays

ark/schema/structure/sequence.ts

@@ -419,13 +419,18 @@ export class SequenceNode extends BaseConstraint<Sequence.Declaration> {
 	}
 
 	traverseApply: TraverseApply<array> = (data, ctx) => {
+		const errorCount = ctx.currentErrorCount
 		let i = 0
 		for (; i < data.length; i++) {
 			traverseKey(
 				i,
 				() => this.elementAtIndex(data, i).node.traverseApply(data[i], ctx),
 				ctx
 			)
+			// bail out of subsequent elements in fail-fast mode (e.g. inside a
+			// union branch) so we don't traverse an element whose basis has
+			// already failed - see https://github.com/arktypeio/arktype/issues/1458
+			if (ctx.failFast && ctx.currentErrorCount > errorCount) return
 		}
 	}
 
@@ -435,9 +440,17 @@ export class SequenceNode extends BaseConstraint<Sequence.Declaration> {
 
 	// minLength/maxLength compilation should be handled by Intersection
 	compile(js: NodeCompiler): void {
+		// like Structure, bail out of subsequent elements in fail-fast mode
+		// (e.g. inside a union branch) so we don't traverse an element whose
+		// basis has already failed - see
+		// https://github.com/arktypeio/arktype/issues/1458
+		if (js.traversalKind === "Apply") js.initializeErrorCount()
+
 		if (this.prefix) {
-			for (const [i, node] of this.prefix.entries())
+			for (const [i, node] of this.prefix.entries()) {
 				js.traverseKey(`${i}`, `data[${i}]`, node)
+				if (js.traversalKind === "Apply") js.returnIfFailFast()
+			}
 		}
 
 		for (const [i, node] of this.defaultablesAndOptionals.entries()) {
@@ -446,6 +459,7 @@ export class SequenceNode extends BaseConstraint<Sequence.Declaration> {
 				js.traversalKind === "Allows" ? js.return(true) : js.return()
 			)
 			js.traverseKey(dataIndex, `data[${dataIndex}]`, node)
+			if (js.traversalKind === "Apply") js.returnIfFailFast()
 		}
 
 		if (this.variadic) {
@@ -457,13 +471,17 @@ export class SequenceNode extends BaseConstraint<Sequence.Declaration> {
 			}
 			js.for(
 				`i < ${this.postfix ? "firstPostfixIndex" : "data.length"}`,
-				() => js.traverseKey("i", "data[i]", this.variadic!),
+				() => {
+					js.traverseKey("i", "data[i]", this.variadic!)
+					return js.traversalKind === "Apply" ? js.returnIfFailFast() : js
+				},
 				this.prevariadic.length
 			)
 			if (this.postfix) {
 				for (const [i, node] of this.postfix.entries()) {
 					const keyExpression = `firstPostfixIndex + ${i}`
 					js.traverseKey(keyExpression, `data[${keyExpression}]`, node)
+					if (js.traversalKind === "Apply") js.returnIfFailFast()
 				}
 			}
 		}

ark/type/__tests__/union.test.ts

@@ -48,6 +48,27 @@ contextualize(() => {
 		attest(T.json).equals(type("string|bigint|number|boolean").json)
 	})
 
+	it("union of object arrays doesn't throw on non-object element", () => {
+		// https://github.com/arktypeio/arktype/issues/1458
+		// checking a later element whose basis (object) fails must not attempt
+		// an `in` check against a primitive earlier collected element
+		const TypeAB = type.or("string", { objB: "string" })
+		const TypeC = type({ objC: "string" })
+		const TypeABC = type([TypeAB.array(), "|", TypeC.array()])
+
+		attest(
+			TypeABC([{ objB: "text b" }, "test a", { objC: "text c" }]).toString()
+		).snap(
+			"value at [2].objB must be a string (was missing) or [0].objC must be a string (was missing)"
+		)
+
+		attest(
+			TypeABC(["test a", { objB: "text b" }, { objC: "text c" }]).toString()
+		).snap(
+			"value at [2].objB must be a string (was missing) or [0] must be an object (was a string)"
+		)
+	})
+
 	it("length stress", () => {
 		// as of TS 5.1, can handle a max of 46 branches before an inifinitely
 		// deep error not the end of the world if this changes slightly, but