Error gracefully when encountering date values in TOML config files (#11651)

* fix: automatically convert TOML Date values in vars to strings

TOML parses unquoted date values like DATE = 2024-01-01 as Date objects.
Previously this caused a confusing error from Miniflare. Now wrangler
automatically converts Date values to ISO date strings (YYYY-MM-DD format)
and shows a warning suggesting to wrap the value in quotes.

Co-authored-by: Dario Piotrowicz <dario@cloudflare.com>

* error insted of trying to convert to string

* Apply suggestions from code review

Co-authored-by: Victor Berchet <victor@suumit.com>

* Apply suggestions from code review

Co-authored-by: Victor Berchet <victor@suumit.com>

* Apply suggestions from code review

* use hardcoded example

* create toml dates using smol-toml in tests

---------

Co-authored-by: OpenCode Claude <opencode-claude@anthropic.com>
Co-authored-by: Victor Berchet <victor@suumit.com>

Author: 3 people

.changeset/floppy-tips-play.md

@@ -0,0 +1,7 @@
+---
+"wrangler": patch
+---
+
+Surface a more helpful error message for TOML Date, Date-Time, and Time values in `vars`
+
+TOML parses unquoted date/time values like `DATE = 2024-01-01` as objects. Previously this would cause an unhelpful error message further down the stack. Now wrangler surfaces a more helpful error message earlier, telling you to quote the value as a string, e.g. `DATE = "2024-01-01"`.

.changeset/tangy-knives-allow.md

@@ -0,0 +1,7 @@
+---
+"@cloudflare/workers-utils": patch
+---
+
+Surface error in diagnostics when TOML date/time values are used in `vars`
+
+TOML parses unquoted date/time values like `DATE = 2024-01-01` as TOML Date, Date-Time, and Time values. The config validation now surfaces an error in the diagnostics result when this type of values are encountered, with a clear message telling you to quote the value as a string, e.g. `DATE = "2024-01-01"`.

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

@@ -2069,9 +2069,9 @@ const validateVars =
 		let isValid = true;
 		const fieldPath =
 			config === undefined ? `${field}` : `env.${envName}.${field}`;
-		const configVars = Object.keys(config?.vars ?? {});
-		// If there are no top level vars then there is nothing to do here.
-		if (configVars.length > 0) {
+
+		// Validate var values if vars is defined
+		if (value !== undefined) {
 			if (typeof value !== "object" || value === null) {
 				diagnostics.errors.push(
 					`The field "${fieldPath}" should be an object but got ${JSON.stringify(
@@ -2080,6 +2080,23 @@ const validateVars =
 				);
 				isValid = false;
 			} else {
+				// Check each var value for invalid types (e.g., Date objects)
+				for (const [varName, varValue] of Object.entries(value)) {
+					if (varValue instanceof Date) {
+						diagnostics.errors.push(
+							`The field "${fieldPath}.${varName}" is a TOML date, which is not supported. ` +
+								`Please use a string instead, e.g. ${varName} = "2025-12-19".`
+						);
+						isValid = false;
+					}
+				}
+			}
+		}
+
+		// Check for vars that exist at top level but not in the current environment
+		const configVars = Object.keys(config?.vars ?? {});
+		if (configVars.length > 0) {
+			if (typeof value === "object" && value !== null) {
 				for (const varName of configVars) {
 					if (!(varName in value)) {
 						diagnostics.warnings.push(

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

@@ -1,4 +1,5 @@
 import path from "node:path";
+import TOML from "smol-toml";
 import { describe, expect, it, test, vi } from "vitest";
 import { normalizeAndValidateConfig } from "../../../src/config/validation";
 import { normalizeString } from "../../../src/test-helpers";
@@ -5469,6 +5470,51 @@ describe("normalizeAndValidateConfig()", () => {
 				      Please add \\"unsafe\\" to \\"env.ENV1\\"."
 			`);
 		});
+
+		it("should error on Date values in vars (parsed by TOML)", () => {
+			const rawConfig = TOML.parse(`
+				[vars]
+				VALID_VAR = "some string"
+				DATE_VAR = 2024-01-01
+			`) as unknown as RawConfig;
+
+			const { diagnostics } = normalizeAndValidateConfig(
+				rawConfig,
+				undefined,
+				undefined,
+				{ env: undefined }
+			);
+
+			expect(diagnostics.hasErrors()).toBe(true);
+			expect(diagnostics.renderErrors()).toMatchInlineSnapshot(`
+				"Processing wrangler configuration:
+				  - The field \\"vars.DATE_VAR\\" is a TOML date, which is not supported. Please use a string instead, e.g. DATE_VAR = \\"2025-12-19\\"."
+			`);
+		});
+
+		it("should error on Date values in env vars (parsed by TOML)", () => {
+			const rawConfig = TOML.parse(`
+				[env.production.vars]
+				VALID_VAR = "some string"
+				RELEASE_DATE = 2025-06-15
+			`) as unknown as RawConfig;
+
+			const { diagnostics } = normalizeAndValidateConfig(
+				rawConfig,
+				undefined,
+				undefined,
+				{ env: "production" }
+			);
+
+			expect(diagnostics.hasErrors()).toBe(true);
+			expect(diagnostics.renderErrors()).toMatchInlineSnapshot(`
+				"Processing wrangler configuration:
+
+				  - \\"env.production\\" environment configuration
+				    - The field \\"env.production.vars.RELEASE_DATE\\" is a TOML date, which is not supported. Please use a string instead, e.g. RELEASE_DATE = \\"2025-12-19\\"."
+			`);
+		});
+
 		it("should error on node_compat", () => {
 			const { diagnostics } = normalizeAndValidateConfig(
 				// @ts-expect-error node_compat has been removed