Avoid writing gitattributes file unless necessary

[vinistock]

Motivation

When studying the memory bloat for the Tapioca add-on, ObjectSpace.dump_all consistently reports the File.write line for writing the git attributes file as the place in the code retaining the most memory.

I did a few tests and it's something to do with the content. If I get rid of the content variable and just use an empty string, then this line no longer appears in the dump as the top retained memory.

I cannot explain why this is the case given that the heredocs used for the content are frozen strings. I honestly have no idea what's happening here. But avoiding writing the file if it's already there removes this line from the top offenders and no longer retains memory.

Implementation

Started checking if the file exists before writing it.