External redirects break static build

[philipschm1tt]

Astro Info

Astro                    v5.2.3
Node                     v20.12.2
System                   Windows (x64)
Package Manager          pnpm
Output                   static
Adapter                  none
Integrations             none

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

Tested with Astro 5.2.0 and 5.2.3: the build of our static site fails because of external redirects with the following errors (verbose):

On build (not dev):

15:27:52 ▶ /mytest
  astro:build Generating: /mytest +1ms
15:27:52   └─ /mytest/index.html  astro:build Generating: /mytest +1ms
  astro:telemetry {
  astro:telemetry   context: {
  astro:telemetry     isGit: true,
  astro:telemetry     anonymousProjectId: '...',
  astro:telemetry     packageManager: 'pnpm',
  astro:telemetry     packageManagerVersion: '9.15.4',
  astro:telemetry     anonymousId: '...',
  astro:telemetry     anonymousSessionId: '...'
  astro:telemetry   },
  astro:telemetry   meta: {
  astro:telemetry     nodeVersion: '20.12.2',
  astro:telemetry     viteVersion: '6.0.3',
  astro:telemetry     astroVersion: '5.2.3',
  astro:telemetry     systemPlatform: 'win32',
  astro:telemetry     systemRelease: '10.0.22631',
  astro:telemetry     systemArchitecture: 'x64',
  astro:telemetry     cpuCount: 12,
  astro:telemetry     cpuModel: 'Intel(R) Xeon(R) E-2186M  CPU @ 2.90GHz',
  astro:telemetry     cpuSpeed: 2904,
  astro:telemetry     memoryInMb: 32549,
  astro:telemetry     isDocker: false,
  astro:telemetry     isTTY: true,
  astro:telemetry     isWSL: false,
  astro:telemetry     isCI: false,
  astro:telemetry     ciName: null
  astro:telemetry   }
  astro:telemetry } +9s
  astro:telemetry [
  astro:telemetry   {
  astro:telemetry     "eventName": "ASTRO_CLI_ERROR",
  astro:telemetry     "payload": {
  astro:telemetry       "name": "TypeError",
  astro:telemetry       "cliCommand": "build",
  astro:telemetry       "isFatal": true,
  astro:telemetry       "anonymousMessageHint": "immutable"
  astro:telemetry     }
  astro:telemetry   }
  astro:telemetry ] +0ms
immutable
  Stack trace:
    at _Headers.set (node:internal/deps/undici/undici:2413:17)
    at async file:///D:/Website/website/node_modules/.pnpm/astro@5.2.3_@types+node@22.13.0_jiti@2.4.2_rollup@4.34.0_typescript@5.7.3_yaml@2.7.0/node_modules/astro/dist/i18n/middleware.js:49:22
    at async RenderContext.render (file:///D:/Website/website/node_modules/.pnpm/astro@5.2.3_@types+node@22.13.0_jiti@2.4.2_rollup@4.34.0_typescript@5.7.3_yaml@2.7.0/node_modules/astro/dist/core/render-context.js:202:22)
    at async generatePathWithLogs (file:///D:/Website/website/node_modules/.pnpm/astro@5.2.3_@types+node@22.13.0_jiti@2.4.2_rollup@4.34.0_typescript@5.7.3_yaml@2.7.0/node_modules/astro/dist/core/build/generate.js:138:21)
    at async generatePages (file:///D:/Website/website/node_modules/.pnpm/astro@5.2.3_@types+node@22.13.0_jiti@2.4.2_rollup@4.34.0_typescript@5.7.3_yaml@2.7.0/node_modules/astro/dist/core/build/generate.js:82:7)
 ELIFECYCLE  Command failed with exit code 1.

I can produce the error with our (slimmed down) defineConfig:

export default defineConfig({
	site: "https://www.mydomain.com",
	trailingSlash: "always",
	i18n: {
		defaultLocale: "de",
		locales: ["de", "en"],
		routing: {
			prefixDefaultLocale: false,
		},
		fallback: {
			en: "de",
		},
	},
	redirects: {
		"/mytest": "https://example.com/about",
	},
});

The external redirect matches the documentation of the new feature.
Without the redirects or with non-external redirects the build work.

What's the expected result?

External redirects don't break my build.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-1n3kqdia?file=astro.config.mjs

Participation

• I am willing to submit a pull request for this issue.