Move the free port logic so that loadOptions don't override it

lib/core/src/server/build-dev.js

@@ -16,6 +16,8 @@ import semver from 'semver';
 import { stripIndents } from 'common-tags';
 import Table from 'cli-table3';
 import prettyTime from 'pretty-hrtime';
+import inquirer from 'inquirer';
+import detectFreePort from 'detect-port';
 
 import storybook from './dev-server';
 import { getDevCli } from './cli';
@@ -35,6 +37,12 @@ const writeStats = async (name, stats) => {
   );
 };
 
+const getFreePort = port =>
+  detectFreePort(port).catch(error => {
+    logger.error(error);
+    process.exit(-1);
+  });
+
 async function getServer(app, options) {
   if (!options.https) {
     return http.createServer(app);
@@ -238,7 +246,24 @@ function openInBrowser(address) {
 
 export async function buildDevStandalone(options) {
   try {
-    const { port, host, extendServer } = options;
+    const { host, extendServer } = options;
+
+    const port = await getFreePort(options.port);
+
+    if (!options.ci && !options.smokeTest && options.port != null && port !== options.port) {
+      const { shouldChangePort } = await inquirer.prompt({
+        type: 'confirm',
+        default: true,
+        name: 'shouldChangePort',
+        message: `Port ${
+          options.port
+        } is not available. Would you like to run Storybook on port ${port} instead?`,
+      });
+
+      if (!shouldChangePort) {
+        process.exit(1);
+      }
+    }
 
     // Used with `app.listen` below
     const listenAddr = [port];

lib/core/src/server/cli/dev.js

@@ -1,16 +1,9 @@
 import program from 'commander';
 import chalk from 'chalk';
-import detectFreePort from 'detect-port';
 import inquirer from 'inquirer';
 import { logger } from '@storybook/node-logger';
 import { parseList, getEnvConfig } from './utils';
 
-const getFreePort = port =>
-  detectFreePort(port).catch(error => {
-    logger.error(error);
-    process.exit(-1);
-  });
-
 async function getCLI(packageJson) {
   process.env.NODE_ENV = process.env.NODE_ENV || 'development';
 
@@ -64,22 +57,7 @@ async function getCLI(packageJson) {
     program.port = parseInt(program.port, 10);
   }
 
-  const port = await getFreePort(program.port);
-
-  if (!program.ci && !program.smokeTest && program.port != null && port !== program.port) {
-    const { shouldChangePort } = await inquirer.prompt({
-      type: 'confirm',
-      default: true,
-      name: 'shouldChangePort',
-      message: `Port ${program.port} is not available.
-Would you like to run Storybook on port ${port} instead?`,
-    });
-    if (!shouldChangePort) {
-      process.exit(1);
-    }
-  }
-
-  return { ...program, port };
+  return { ...program };
 }
 
 export default getCLI;