feat(nuxi): load `.env` when previewing builds (#4016)

docs/content/3.docs/1.usage/8.cli.md

@@ -67,6 +67,10 @@ Option        | Default          | Description
 
 This command sets `process.env.NODE_ENV` to `production`. To override, define `NODE_ENV` in a `.env` file or as command-line argument.
 
+::alert{type=info}
+For convenience, in preview mode, your `.env` file will be loaded into `process.env`. (However, in production you will need to ensure your environment variables are set yourself.)
+::
+
 ## Info
 
 ```{bash}

packages/nuxi/package.json

@@ -24,6 +24,7 @@
     "@types/mri": "^1.1.1",
     "@types/rimraf": "^3",
     "@types/semver": "^7",
+    "c12": "^0.2.4",
     "chokidar": "^3.5.3",
     "clear": "^0.1.0",
     "clipboardy": "^3.0.0",

packages/nuxi/src/commands/preview.ts

@@ -1,6 +1,7 @@
 import { existsSync, promises as fsp } from 'fs'
 import { dirname, relative } from 'path'
 import { execa } from 'execa'
+import { loadDotenv } from 'c12'
 import { resolve } from 'pathe'
 import consola from 'consola'
 
@@ -34,6 +35,11 @@ export default defineNuxtCommand({
       process.exit(1)
     }
 
+    if (existsSync(resolve(rootDir, '.env'))) {
+      consola.info('Loading `.env`. This will not be loaded when running the server in production.')
+      process.env = await loadDotenv({ cwd: rootDir, fileName: '.env', env: process.env })
+    }
+
     consola.info('Starting preview command:', nitroJSON.commands.preview)
     const [command, ...commandArgs] = nitroJSON.commands.preview.split(' ')
     consola.log('')

yarn.lock

@@ -15369,6 +15369,7 @@ __metadata:
     "@types/mri": ^1.1.1
     "@types/rimraf": ^3
     "@types/semver": ^7
+    c12: ^0.2.4
     chokidar: ^3.5.3
     clear: ^0.1.0
     clipboardy: ^3.0.0