This post got me thinking that it'd be interesting if instead of being given an explicit list of files to watch for changes to, the list of files were inferred with an LD_PRELOAD that listened for `open` / `stat` / etc. system calls that a process ran.

For example, in the example on the blog post, `git ls-files` will almost certainly ignore autogenerated build files, but it's possible for one of those files to change without the output of `git ls-files` changing. Similarly for things like third party packages that are installed system-wide.

With an LD_PRELOAD, all you'd need to do is

    my-watcher ruby foo.rb

and the watcher would figure out which other Ruby files were opened, be them git versioned Ruby files in the current folder, or Ruby gems / Ruby VM dependencies in $HOME/.rbenv/, or system packages in /usr/local, or config files in /etc, ...

I guess I wouldn't actually be surprised to hear if someone has built this already.

fabricate.py (https://github.com/brushtechnology/fabricate), based off the now ancient memoize.py.

In my experience with C/++, it is faster to combine Make & ccache: just have every C file depend on every header file, and let ccache decide if it needs to be rebuilt.