ref: 80f64cfcdafd3d0c4578ad7d559f38018d583c15
parent: 1dc1ed786fda790f60f2fe9f8e7c404c73ae64da
author: Simon Tatham <anakin@pobox.com>
date: Tue Jan 17 14:00:17 EST 2023
Avoid unnecessary timestamp bumps on generated-games.h. If I re-run cmake in a Unix build directory, it unconditionally rewrites generated-games.h, which causes fuzzpuzz to be rebuilt. This is a waste of effort in the extremely common case where the rewritten generated-games.h is identical to the old one. Now we write the data to a temporary file first, and use cmake's 'configure_file' command to copy that to generated-games.h, because it so happens that configure_file checks if the two files are identical and avoids updating the timestamp on the destination file if so. (This will presumably also be a beneficial change on any other platform that uses generated_games.h in the build, such as OS X. I just hadn't noticed until it hit the build I most often re-run in an existing build directory.) cmake 3.21 has a more intuitively spelled command I could have used, called 'file(COPY_FILE src dst ONLY_IF_DIFFERENT)'. But we currently permit cmake all the way back to 3.5, so I can't use that.