Here's an earlier comment I wrote about it, which is also in the middle of a discussion about Tup, funnily enough: https://news.ycombinator.com/item?id=4190804

I'm still using Fabricate quite happily today for personal projects in a variety of languages, though I've come to realise that the main downside of it is that programs run slower under strace - a typical gcc invocation to create a single object file might take say, 40% longer. Fabricate.py is also then quite slow to parse the textual output from strace.

Inspired by https://blog.nelhage.com/2010/08/write-yourself-an-strace-in... I wrote a mini-strace that's hard coded to catch the open() and other relevant calls as fast as possible. That helped a fair bit. I've done a lot of hacking on my own copy of Fabricate too which helped a bit, but ultimately I ought to make it do the dependency parsing and saving in a seperate thread, which should help a lot - I'm still not doing parallel builds so I do have spare cores sitting there doing nothing.

I tried a FUSE backend (https://github.com/SimonAlfie/fabricate/pull/60) whereby the filesystem tells you what's being accessed, and that's practically the same as full speed but the downside is that the path jiggery-pokery involved then causes some subsequent problems with eg. gdb not being able to find source files. I've gone back to the strace method for now.

Despite all these niggles, I still use this system wherever possible because it's so, so good having a 'proper' programming language to run my builds, and being able to work forwards in the manner of a shell script. And yeah the automatic detection of changes ultimately saves a lot of time. I can share some of my hacked-up scripts if anyone's interested.