fix: improve error message when entry is missing w/ --target lib

close #1051

packages/@vue/cli-service/lib/commands/build/resolveLibConfig.js

@@ -1,15 +1,31 @@
+const fs = require('fs')
 const path = require('path')
 
 module.exports = (api, { entry, name }, options) => {
+  // setting this disables app-only configs
+  process.env.VUE_CLI_TARGET = 'lib'
+  // inline all static asset files since there is no publicPath handling
+  process.env.VUE_CLI_INLINE_LIMIT = Infinity
+
+  const { log, error } = require('@vue/cli-shared-utils')
+  const abort = msg => {
+    log()
+    error(msg)
+    process.exit(1)
+  }
+
+  if (!fs.existsSync(api.resolve(entry))) {
+    abort(
+      `Failed to resolve lib entry: ${entry}${entry === `src/App.vue` ? ' (default)' : ''}. ` +
+      `Make sure to specify the correct entry file.`
+    )
+  }
+
   const libName = (
     name ||
     api.service.pkg.name ||
     path.basename(entry).replace(/\.(jsx?|vue)$/, '')
   )
-  // setting this disables app-only configs
-  process.env.VUE_CLI_TARGET = 'lib'
-  // inline all static asset files since there is no publicPath handling
-  process.env.VUE_CLI_INLINE_LIMIT = Infinity
 
   function genConfig (format, postfix = format, genHTML) {
     const config = api.resolveChainableWebpackConfig()