The purpose of this release is to provide a deprecation message to users of ApolloCodegenLib who are scripting their code generation in advance of an upcoming change to our libraries and repo structure. Beginning with the upcoming 1.6.0 release the code generation libraries will be their own SPM package in their own repo which will require you to add a new dependency to you project in order for your code generation scripting to compile. More information can be found in our announcement of this change.
If you would like to avoid this deprecation warning in your builds feel free to stay on 1.5.1 or earlier, this warning will be gone in the 1.6.0 release
PR containing deprecation warning for reference: #3243.