Docker on Windows with Dart Docker Image
The issue 20397 explains (credit: Sebastiaan van Stijn - thaJeztah)
That warning was added, because the Windows filesystem does not have an option to mark a file as 'executable'.
Building a linux image from a Windows machine would therefore break the image if a file has to be marked executable.For that reason, files are marked executable by default when building from a windows client; the warning is there so that you are notified of that, and (if needed), modify the Dockerfile to change/remove the executable bit afterwards.
I like to add in the Dockerfile, after a COPY, a RUN CHMOD +x aFile_I_Just_Copied