don't re-build a unchanged cmake dependency

[Licenser]

When compiling a project that has a cmake dependency it'll re-compile the dependency every time cargo is run.

[alexcrichton]

This crate already has some logic to avoid rebuilding too much, but it sounds like it's still happening for you? Can you post an example to poke around with?

[anderslanglands]

I'm having a similar issue. I'm not sure what exactly is getting rebuilt (is there any way to get more output from cmake-rs from cargo as opposed to just the progress bar?) but it's not the whole cmake project as that would take a really long time. My project is here: https://github.com/anderslanglands/oiio-rs

Changing anything in the rust part causes cmake to rebuild even though always_configure is false.

[RReverser]

Same here, I tried setting always_configure(false) but no effect, still rebuilds from scratch.

[RReverser]

For now used a workaround

let built_marker = out_dir.join(".built");

if !built_marker.exists() {
    cmake::/* ... */

    std::fs::File::create(built_marker).unwrap();
}

this will likely cause issues when some flags change, but at least avoids rebuilding the C++ dependency of my project all the time.