[workers-utils] Report a non-array queues.consumers as a config error instead of crashing

.changeset/queues-consumers-not-array.md

@@ -0,0 +1,7 @@
+---
+"@cloudflare/workers-utils": patch
+---
+
+Report an invalid `queues.consumers` value as a configuration error instead of crashing
+
+Previously, setting `queues.consumers` to something other than an array (for example `null` or a string) could crash Wrangler or produce a flood of confusing extra errors. You now get a single clear message telling you the field must be an array.

packages/workers-utils/src/config/validation.ts

@@ -5114,13 +5114,13 @@ function validateQueues(envName: string): ValidatorFn {
 					)}.`
 				);
 				isValid = false;
-			}
-
-			for (let i = 0; i < consumers.length; i++) {
-				const consumer = consumers[i];
-				const consumerPath = `${fieldPath}.consumers[${i}]`;
-				if (!validateConsumer(diagnostics, consumerPath, consumer, config)) {
-					isValid = false;
+			} else {
+				for (let i = 0; i < consumers.length; i++) {
+					const consumer = consumers[i];
+					const consumerPath = `${fieldPath}.consumers[${i}]`;
+					if (!validateConsumer(diagnostics, consumerPath, consumer, config)) {
+						isValid = false;
+					}
 				}
 			}
 		}

packages/workers-utils/tests/config/validation/normalize-and-validate-config.test.ts

@@ -4758,6 +4758,34 @@ describe("normalizeAndValidateConfig()", () => {
 				`);
 			});
 
+			it("should error if queues.consumers is null", ({ expect }) => {
+				const { diagnostics } = normalizeAndValidateConfig(
+					{ queues: { consumers: null } } as unknown as RawConfig,
+					undefined,
+					undefined,
+					{ env: undefined }
+				);
+
+				expect(diagnostics.renderErrors()).toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - The field "queues.consumers" should be an array but got null."
+				`);
+			});
+
+			it("should error once if queues.consumers is a string", ({ expect }) => {
+				const { diagnostics } = normalizeAndValidateConfig(
+					{ queues: { consumers: "my-queue" } } as unknown as RawConfig,
+					undefined,
+					undefined,
+					{ env: undefined }
+				);
+
+				expect(diagnostics.renderErrors()).toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - The field "queues.consumers" should be an array but got "my-queue"."
+				`);
+			});
+
 			it("should error if queues producer bindings are not valid", ({
 				expect,
 			}) => {