pod install 报错 [!] Unable to determine Swift version for the following pods:

某个情况下，执行 pod install 报错：
[!] Unable to determine Swift version for the following pods:

• xxx does not specify a Swift version and none of the targets (Runner) integrating it have the SWIFT_VERSION attribute set. Please contact the author or set the SWIFT_VERSION attribute in at least one of the targets that integrate this pod.
• xxx does not specify a Swift version and none of the targets (Runner) integrating it have the SWIFT_VERSION attribute set. Please contact the author or set the SWIFT_VERSION attribute in at least one of the targets that integrate this pod.

解决办法：在Xcode 项目build-setting 里面的User-Defined 添加 SWIFT_VERSION key 5.0（具体的key根据你使用的swift版本填写）如下图：

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