[bluGill]

What do you want in a maximum? Cmake is a local maximum if popularity is important, which it should be. Because cmake is popular you can find lots of things that work with it, and when you have problems other experts who can help.

For build systems few people really want to become experts so finding them is important.

Don't take the above as saying cmake is the best, it deserves most criticism. However the alternatives are probably not compelling just because they are not popular.

[jcranmer]

A build system is largely declarative--it tends to boil down to defining rules like "how to compile a source file", "how to build a library", etc., along with the lists of things those rules need to be applied to, with there being a confusing three-way tug-of-war between the user, the project, and the system over how to override stuff and who wins out. The end result should be that you should ideally be able to query the build system to figure out the underlying declarative pieces of it pretty easily (e.g., list all of the C++ compiler invocations, list all of the package dependencies, etc.).

CMake is like halfway there or so, combined with a shell-like language that has some annoying issues (e.g., functions are statements, not expressions, so if you want to do dirname(dirname(foo)), that's two calls to PARENT_PATH). It does a better job than autoconf/make in that it doesn't invite you to resort to shell almost immediately, but that is admittedly a low bar.

[bluGill]

While I want a.build system to be declaritive, in the real world there is always complexity they designers didn't think of. So I need an escape to build something they didn't think of.

Though it would be nice if that thing I.build could then be declarative.