fix: force serverless target

Author: ascorbic

helpers/getNextConfig.js

@@ -1,7 +1,6 @@
 'use strict'
 
 const { cwd: getCwd } = require('process')
-const { resolve } = require('path')
 
 const moize = require('moize')
 

helpers/hasCorrectNextConfig.js

@@ -1,5 +1,4 @@
 const getNextConfig = require('./getNextConfig')
-
 // Checks if site has the correct next.config.js
 const hasCorrectNextConfig = async ({ nextConfigPath, failBuild }) => {
   // In the plugin's case, no config is valid because we'll make it ourselves
@@ -12,9 +11,27 @@ const hasCorrectNextConfig = async ({ nextConfigPath, failBuild }) => {
   const isValidTarget = acceptableTargets.includes(target)
   if (!isValidTarget) {
     console.log(
-      `Your next.config.js must set the "target" property to one of: ${acceptableTargets.join(', ')}. Update the
-      target property to allow this plugin to run.`,
+      `The "target" config property must be one of "${acceptableTargets.join('", "')}". Setting it to "serverless".`,
     )
+
+    /* eslint-disable fp/no-delete, node/no-unpublished-require */
+
+    // We emulate Vercel so that we can set target to serverless if needed
+    process.env.NOW_BUILDER = true
+    // If no valid target is set, we use an internal Next env var to force it
+    process.env.NEXT_PRIVATE_TARGET = 'serverless'
+
+    // 🐉 We need Next to recalculate "isZeitNow" var so we can set the target, but it's
+    // set as an import side effect so we need to clear the require cache first. 🐲
+    // https://github.com/vercel/next.js/blob/canary/packages/next/telemetry/ci-info.ts
+
+    delete require.cache[require.resolve('next/dist/telemetry/ci-info')]
+    delete require.cache[require.resolve('next/dist/next-server/server/config')]
+
+    // Clear memoized cache
+    getNextConfig.clear()
+
+    /* eslint-enable fp/no-delete, node/no-unpublished-require */
   }
 
   return isValidTarget

index.js

@@ -28,21 +28,8 @@ module.exports = {
     if (hasNoPackageJson) {
       return failBuild('Could not find a package.json for this project')
     }
-
-    const pluginNotNeeded = await doesNotNeedPlugin({ netlifyConfig, packageJson, failBuild })
-
-    if (!pluginNotNeeded) {
-      const nextConfigPath = await findUp('next.config.js')
-      if (nextConfigPath === undefined) {
-        // Create the next config file with target set to serverless by default
-        const nextConfig = `
-            module.exports = {
-              target: 'serverless'
-            }
-          `
-        await pWriteFile('next.config.js', nextConfig)
-      }
-    }
+    // Populates the correct config if needed
+    await doesNotNeedPlugin({ netlifyConfig, packageJson, failBuild })
 
     // Because we memoize nextConfig, we need to do this after the write file
     const nextConfig = await getNextConfig(utils.failBuild)