I do not have ninja in the system, and use instead that ninja which is shipped with the Qt installer.

With Qt Creator master and an msvc kit, this does not work, anymore. I get this error message when trying to configure a project:

CMake Error: CMake was unable to find a build program corresponding to "Ninja".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.

CMakeBuildConfiguration::addToEnvironment() is called multiple times and it does add ninja to "Path". However, when CMakeProcess::run() is called, the passed-in Utils::Environment does indeed not have ninja in "Path".

If I use a MinGW kit, the path does contain ninja and configuration succeeds. So, this seems to be specific to the Msvc toolchain.