Invalid `Podfile` file: undefine

flutter与iOS混编的项目，之前一直pod install 正常，有一天想研究下vscode编写插件，就安装了npm，结果再执行pod install 报错了。
在iOS工程目录下执行pod install 报错：

Invalid `Podfile` file: undefined method `exists?' for File:Class

在flutter工程目录下执行flutter build ios，报错：

CocoaPods' output:
↳

    [!] Invalid `Podfile` file: undefined method `exists?' for File:Class.

     #  from /Users/admin/Desktop/flutter_plugin/.ios/Podfile:31
     #  -------------------------------------------
     #    use_frameworks!
     >    flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
     #  
     #  -------------------------------------------

    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:335:in `rescue in block in from_ruby'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:329:in `block in from_ruby'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:50:in `instance_eval'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:50:in `initialize'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:327:in `new'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:327:in `from_ruby'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-core-1.11.3/lib/coco
    apods-core/podfile.rb:293:in `from_file'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-1.11.3/lib/cocoapods
    /config.rb:205:in `podfile'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-1.11.3/lib/cocoapods
    /command.rb:160:in `verify_podfile_exists!'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-1.11.3/lib/cocoapods
    /command/install.rb:46:in `run'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/claide-1.1.0/lib/claide/comman
    d.rb:334:in `run'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-1.11.3/lib/cocoapods
    /command.rb:52:in `run'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/gems/cocoapods-1.11.3/bin/pod:55:in
    `<top (required)>'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/bin/pod:25:in `load'
    /opt/homebrew/Cellar/cocoapods/1.11.3_1/libexec/bin/pod:25:in `<main>'

Error running pod install

解决办法： 删除cocoapod 1.11.3版本，安装1.11.2版本
删除cocoapod.

$ sudo gem uninstall cocoapods -v (移除的版本号)

安装1.11.2

sudo gem install cocoapods -v (要安装的版本号)

重新pod install 解决

删除cocoapod不彻底时，可参考
https://blog.csdn.net/Qyee16/article/details/52055084?locationNum=7&fps=1