chore: show warnings in build debug mode (vuejs#285)

Author: meteorlxy

lib/build.js

@@ -103,6 +103,11 @@ module.exports = async function build (sourceDir, cliOptions = {}) {
           reject(new Error(`Failed to compile with errors.`))
           return
         }
+        if (cliOptions.debug && stats.hasWarnings()) {
+          stats.toJson().warnings.forEach(warning => {
+            console.warn(warning)
+          })
+        }
         resolve(stats.toJson({ modules: false }))
       })
     })