feat: set baseUrl via runtimeConfig (nuxt-modules#1920)

* feat: add baseUrl runtimeConfig support

* test: add baseUrl runtimeConfig test

* docs: add runtimeConfig page

* docs: fix incorrect environment variable name

docs/content/3.options/2.routing.md

@@ -13,6 +13,8 @@ The fallback base URL to use as a prefix for alternate URLs in `hreflang` tags.
 
 Can also be a function (will be passed a Nuxt Context as a parameter) that returns a string. Useful to make base URL dynamic based on request headers.
 
+This property can also be set using [`runtimeConfig`](./runtime-config).
+
 ::alert{type="info"}
 
 It's especially important to set this option when using SEO features, in which case it's required that generated SEO tags use fully-qualified URLs.

docs/content/3.options/7.runtime-config.md

@@ -0,0 +1,47 @@
+# Runtime config
+
+Some options can be set via the `runtimeConfig`, setting options this way makes it possible to override these after building using environment variables.
+
+---
+
+## Usage
+
+If you want to use environment variables to change [supported options](#supported-options), you will have to set these in `runtimeConfig.public.i18n`. 
+
+The module configuration takes precedence, options set through `runtimeConfig` will only be used if they are unset.
+
+Setting `baseUrl` through `runtimeConfig` would look like this:
+
+```ts {}[nuxt.config.ts]
+export default defineNuxtConfig({
+  runtimeConfig: {
+    public: {
+      i18n: {
+         baseUrl: 'https://example.com',
+      }
+    }
+  },
+  modules: [
+    '@nuxtjs/i18n'
+  ],
+  i18n: {
+    // Leave options unset that you want to set using `runtimeConfig`
+    // baseUrl: 'https://example.com',
+  }
+})
+```
+
+With this configuration you will be able to override the `baseUrl` option by setting the `NUXT_PUBLIC_I18N_BASE_URL` environment variable. You can read more about how this works in the [Nuxt documentation](https://nuxt.com/docs/guide/going-further/runtime-config#environment-variables).
+
+##  Supported options
+
+These options can be set using `runtimeConfig`:
+* [`baseUrl`](./routing#baseUrl)
+
+::alert{type=warning}
+Only [serializable values are supported](https://nuxt.com/docs/guide/going-further/runtime-config#serialization) in `runtimeConfig`, options set this way may not support all available types (such as functions) as would normally be possible using the default configuration.
+::
+
+::alert{type=info}
+If you would like other options to be supported, open an issue describing your use case, or open a PR adding to add support yourself!
+::

specs/seo/baseUrl_runtimeConfig.spec.ts

@@ -0,0 +1,35 @@
+import { expect, test } from 'vitest'
+import { fileURLToPath } from 'node:url'
+import { setup, $fetch } from '@nuxt/test-utils'
+import { getDom, getDataFromDom, assertLocaleHeadWithDom } from '../helper'
+
+const configDomain = 'https://runtime-config-domain.com'
+await setup({
+  rootDir: fileURLToPath(new URL(`../fixtures/basic`, import.meta.url)),
+  browser: true,
+  // overrides
+  nuxtConfig: {
+    runtimeConfig: {
+      public: {
+        i18n: {
+          baseUrl: configDomain
+        }
+      }
+    },
+    i18n: {
+      //   debug: true,
+      defaultLocale: 'en',
+      baseUrl: ''
+    }
+  }
+})
+
+test('render seo tags with baseUrl', async () => {
+  const html = await $fetch('/?noncanonical')
+  const dom = getDom(html)
+  await assertLocaleHeadWithDom(dom, '#home-use-locale-head')
+
+  const links = getDataFromDom(dom, '#home-use-locale-head').link
+  const i18nCan = links.find(x => x.id === 'i18n-can')
+  expect(i18nCan.href).toContain(configDomain)
+})

src/runtime/utils.ts

@@ -485,18 +485,27 @@ export function extendBaseUrl<Context extends NuxtApp = NuxtApp>(
 ): BaseUrlResolveHandler<Context> {
   return (context: Context): string => {
     if (isFunction(baseUrl)) {
-      return baseUrl(context)
+      const baseUrlResult = baseUrl(context)
+      __DEBUG__ && console.log('baseUrl: using localeLoader function -', baseUrlResult)
+      return baseUrlResult
     }
 
     const { differentDomains, localeCodeLoader, normalizedLocales } = options
     const localeCode = isFunction(localeCodeLoader) ? localeCodeLoader() : localeCodeLoader
     if (differentDomains && localeCode) {
       const domain = getDomainFromLocale(localeCode, normalizedLocales, options.nuxt)
       if (domain) {
+        __DEBUG__ && console.log('baseUrl: using differentDomains -', domain)
         return domain
       }
     }
 
+    const config = context.$config?.public?.i18n
+    if (config?.baseUrl) {
+      __DEBUG__ && console.log('baseUrl: using runtimeConfig -', config.baseUrl)
+      return config.baseUrl
+    }
+
     return baseUrl
   }
 }