make2ninja

This repository contains a tool for converting Makefile builds into Ninja builds, with the intent of speeding up a build.

I've found that it decreased the build time of the software I was working on by 10% for a full rebuild, and 30% for a single file change. That software has a pretty flat build tree, and a single Makefile, so I expect greater speedups are possible for some systems. On the other hand, make2ninja does not express the entire dependency graph, which might result in builds that are slower then necessary?

Already this is a pretty nice improvement- its a tiny little script that didn't take much time to create, and I get a bit faster builds! No complaints here.

The inspiration for this tool was https://github.com/lindenb/makefile2graph, which parses the result of:

make -Bnd

to create a graph of a make build's dependencies. It was simple to parse the output, and then generate a Ninja file instead.

The current implementation is very raw- it is the code I got working while thinking through this idea.

Usage

Simply try

make -Bnd | python make2ninja.py > build.ninja

to generate a build.ninja file.

Multiple ninja files could be created for different make builds- ninja is more explicit, so certain make builds may result in different ninja files (like release vs debug).

Special Cases

I'm sure there are many special cases in Makefiles that I could have missed. The one that make2ninja does handle is where files are given without paths, and are resolved by VPATH (which I make use of a great deal in Makefiles).

Possible Improvements

This tool could detect .d files in the rules, and add the 'dep' and 'depfile' variables to its output.

Currently make2ninja does not express the entire dependency graph in the ninja file- it takes a topological sort given by make and expresses that. I don't think it would be hard to change this, and it might result in faster builds for more complex projects. I have not looked into this at all.

It could also just be written in a clearer and more organized fashion- its just a proof of concept right now.

In prinicpal something could be done to detect changes in the build to regenerate the file, or incorporate this tool into the make file to regenerate the ninja file somehow. I haven't thought this one through entirely.

Please feel free to fork, PR, or make an issue if this is an interesting or useful tool!