Ninja Multi-Config

Generates multiple build-<Config>.ninja files.

This generator is very much like the Ninja generator, but with some key differences. Only these differences will be discussed in this document.

Unlike the Ninja generator, Ninja Multi-Config generates multiple configurations at once with CMAKE_CONFIGURATION_TYPES instead of only one configuration with CMAKE_BUILD_TYPE. One build-<Config>.ninja file will be generated for each of these configurations (with <Config> being the configuration name.) These files are intended to be run with ninja -f build-<Config>.ninja. A build.ninja file is also generated, using the configuration from either CMAKE_DEFAULT_BUILD_TYPE or the first item from CMAKE_CONFIGURATION_TYPES.

cmake --build . --config <Config> will always use build-<Config>.ninja to build. If no --config argument is specified, cmake --build . will default to build-Debug.ninja, unless a build.ninja is generated (see below), in which case that will be used instead.

Each build-<Config>.ninja file contains <target> targets as well as <target>:<Config> targets, where <Config> is the same as the configuration specified in build-<Config>.ninja Additionally, if cross-config mode is enabled, build-<Config>.ninja may contain <target>:<OtherConfig> targets, where <OtherConfig> is a cross-config, as well as <target>:all, which builds the target in all cross-configs. See below for how to enable cross-config mode.

The Ninja Multi-Config generator recognizes the following variables:

CMAKE_CONFIGURATION_TYPES

Specifies the total set of configurations to build.

CMAKE_CROSS_CONFIGS

Specifies a semicolon-separated list of configurations available from all build-<Config>.ninja files.

CMAKE_DEFAULT_BUILD_TYPE

Specifies the configuration to use by default in a build.ninja file.

CMAKE_DEFAULT_CONFIGS

Specifies a semicolon-separated list of configurations to build for a target in build.ninja if no :<Config> suffix is specified.

Consider the following example:

cmake_minimum_required(VERSION 3.16)
project(MultiConfigNinja C)

add_executable(generator generator.c)
add_custom_command(OUTPUT generated.c COMMAND generator generated.c)
add_library(generated ${CMAKE_BINARY_DIR}/generated.c)

Now assume you configure the project with Ninja Multi-Config and run one of the following commands:

ninja -f build-Debug.ninja generated
# OR
cmake --build . --config Debug --target generated

This would build the Debug configuration of generator, which would be used to generate generated.c, which would be used to build the Debug configuration of generated.

But if CMAKE_CROSS_CONFIGS is set to all, and you run the following instead:

ninja -f build-Release.ninja generated:Debug
# OR
cmake --build . --config Release --target generated:Debug

This would build the Release configuration of generator, which would be used to generate generated.c, which would be used to build the Debug configuration of generated. This is useful for running a release-optimized version of a generator utility while still building the debug version of the targets built with the generated code.