I have a project that I have been working on for a few days and I finally got it to compile cleanly. However, a git clone of the same remote branch (on the same machine, compiled in the same terminal instance) caused a compilation error. A fresh clone on a different machine had the same error. I figured it was an issue with my working directory having some additional untracked files, but I deleted all untracked files to the point where diff says the directories are identical except for things contained in the .git folder. I even checked permissions with tree and compared the resulting files with meld - they were basically identical, although a few source files had slightly different execution permissions.
The error was one that came from a file which I had excluded in the maven-compiler-plugin. This should essentially mean that the filename is never passed to javac, although I don't know exactly how it works under the hood. I realize that clearly the compiler is getting the file from somewhere if it is erroring on code inside it. In the one directory on my computer which worked, there are no errors and it compiles perfectly. On the other clones of the repo (which are, again, identical according to diff) it gives an error on this (excluded) file.
Additional experimentation showed that on a fresh git clone of the remote branch, a cp -R of the local directory, or a git clone of the local directory, compile failed. However, if I did a cp with the --archive option, the compile in the resulting directory succeeded. I narrowed it down to the --preserve=timestamps flag (which is enabled due to the fact that --archive is the same as -dR --preserve=all). If you didn't quite catch that, I'll say it again.
When I copy the directory normally, it refuses to compile properly. Only when the timestamps are preserved does it behave identically to the original directory.
I don't understand this - why does the java compiler (or maven) care about the timestamps?