Add more helpful error messages when validating compatibility date

.changeset/fifty-dots-end.md

@@ -0,0 +1,5 @@
+---
+"wrangler": patch
+---
+
+feat: More helpful error messages when validating compatibility date

packages/wrangler/src/__tests__/configuration.test.ts

@@ -280,6 +280,83 @@ describe("normalizeAndValidateConfig()", () => {
 		`);
 		});
 
+		describe("compatibility_date", () => {
+			it("should allow valid values", () => {
+				const expectedConfig: RawConfig = {
+					compatibility_date: "2024-10-01",
+				};
+
+				const { config, diagnostics } = normalizeAndValidateConfig(
+					expectedConfig,
+					undefined,
+					{ env: undefined }
+				);
+
+				expect(config).toEqual(expect.objectContaining(expectedConfig));
+				expect(diagnostics.hasWarnings()).toBe(false);
+				expect(diagnostics.hasErrors()).toBe(false);
+			});
+
+			it("should error for en-dashes and em-dashes", () => {
+				let expectedConfig: RawConfig = {
+					compatibility_date: "2024–10-01", // en-dash
+				};
+
+				let result = normalizeAndValidateConfig(expectedConfig, undefined, {
+					env: undefined,
+				});
+
+				expect(result.config).toEqual(expect.objectContaining(expectedConfig));
+				expect(result.diagnostics.hasWarnings()).toBe(false);
+				expect(result.diagnostics.hasErrors()).toBe(true);
+
+				expect(normalizeString(result.diagnostics.renderErrors()))
+					.toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - Hyphens (-) should be used rather than en-dashes (—) or em-dashes (–) in the \\"compatibility_date\\" field."
+				`);
+
+				expectedConfig = {
+					compatibility_date: "2024—10-01", // em-dash
+				};
+
+				result = normalizeAndValidateConfig(expectedConfig, undefined, {
+					env: undefined,
+				});
+
+				expect(result.config).toEqual(expect.objectContaining(expectedConfig));
+				expect(result.diagnostics.hasWarnings()).toBe(false);
+				expect(result.diagnostics.hasErrors()).toBe(true);
+
+				expect(normalizeString(result.diagnostics.renderErrors()))
+					.toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - Hyphens (-) should be used rather than en-dashes (—) or em-dashes (–) in the \\"compatibility_date\\" field."
+				`);
+			});
+
+			it("should error for invalid date values", () => {
+				const expectedConfig: RawConfig = {
+					compatibility_date: "abc",
+				};
+
+				const { config, diagnostics } = normalizeAndValidateConfig(
+					expectedConfig,
+					undefined,
+					{ env: undefined }
+				);
+
+				expect(config).toEqual(expect.objectContaining(expectedConfig));
+				expect(diagnostics.hasErrors()).toBe(true);
+
+				expect(normalizeString(diagnostics.renderErrors()))
+					.toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - \\"compatibility_date\\" should be a valid ISO-8601 date (YYYY-MM-DD), but got \\"abc\\"."
+				`);
+			});
+		});
+
 		describe("[site]", () => {
 			it("should override `site` config defaults with provided values", () => {
 				const expectedConfig: RawConfig = {

packages/wrangler/src/config/validation.ts

@@ -1134,7 +1134,7 @@ function normalizeAndValidateEnvironment(
 			topLevelEnv,
 			rawEnv,
 			"compatibility_date",
-			isString,
+			validateCompatibilityDate,
 			undefined
 		),
 		compatibility_flags: inheritable(
@@ -3159,6 +3159,43 @@ const validateConsumer: ValidatorFn = (diagnostics, field, value, _config) => {
 	return isValid;
 };
 
+const isValidDate = (value: string): boolean => {
+	const data = new Date(value);
+	return !isNaN(data.getTime());
+};
+
+const validateCompatibilityDate: ValidatorFn = (diagnostics, field, value) => {
+	if (value === undefined) {
+		return true;
+	}
+
+	if (typeof value !== "string") {
+		diagnostics.errors.push(
+			`Expected "${field}" to be of type string but got ${JSON.stringify(value)}.`
+		);
+		return false;
+	}
+
+	if (
+		value.includes("–") || // en-dash
+		value.includes("—") // em-dash
+	) {
+		diagnostics.errors.push(
+			`Hyphens (-) should be used rather than en-dashes (—) or em-dashes (–) in the "${field}" field.`
+		);
+		return false;
+	}
+
+	if (!isValidDate(value)) {
+		diagnostics.errors.push(
+			`"${field}" should be a valid ISO-8601 date (YYYY-MM-DD), but got ${JSON.stringify(value)}.`
+		);
+		return false;
+	}
+
+	return true;
+};
+
 const validatePipelineBinding: ValidatorFn = (diagnostics, field, value) => {
 	if (typeof value !== "object" || value === null) {
 		diagnostics.errors.push(