Multi configuration builds don't work

[xTachyon]

My CMake knowledge is quite limited, so I'm sorry if I misjudged anything here.

When using a build with multiple configurations set, like this:

cmake .. -DCMAKE_CONFIGURATION_TYPES=Debug;Release

This line using the output_dir var seems to be breaking the build. From what I could test, it looks like output_dir var is empty after the generator expr is evaluated, which results in the command cmake -E make_directory to be called without a string, which triggers the help message for that command and a failed build.

It seems weird for me that stuff like <CONFIG:debug> is not triggered at all when it comes with multi config builds; I don't know what other variant could be used.

Am I doing something wrong or is this just not working?

[jschwe]

Are you using a multi config Generator? E.g. Ninja Multiconfig?

[jschwe]

I've opened #400 to give users a helpful warning if they have misconfigured CMake by setting CMAKE_CONFIGURATION_TYPES, even though the generator they are using is single-config.