Even then the rights get dicey when they include third party libraries and development systems. Doom famously had issues with the sound library they used.
Plus, with commercial software it often happens that the code only builds cleanly on one specific ancient version of a closed source compiler in a specifically tweaked build environment that has been lost to the ages. Having the source helps a lot, but it is not a panacea.
On opens source projects the build system needs to be reasonable enough that anybody can set it up. There are lots of conventions and even tools to help people. On closed source projects it is just Joe the sysadmin who sets up the machines for everybody working on it. Also, open source projects rarely include requirements like "buy a license of this specific version of this proprietary library and install it on your machine".
Doom had the advantage that it was written by a really excellent team with some standout programmers, and it has had plenty of people maintaining the codebase over the years.
> Doom wasn't developed with open source in mind, was it ?
Not sure - Wolfenstein 3D was open sourced in 1995 (two years after Doom was released).
Yet both of these issues seem to plague closed source software more than open source ?
Doom wasn't developed with open source in mind, was it ?
What open source software "only builds cleanly on one specific ancient version of a closed source compiler in a specifically tweaked build environment that has been lost to the ages" ?