New in version 3.19.

Makefile Generators do not repeat custom commands from target dependencies.

Consider a chain of custom commands split across two dependent targets:

add_custom_command(OUTPUT output-not-created
set_property(SOURCE output-not-created PROPERTY SYMBOLIC 1)
add_custom_command(OUTPUT output-created
add_custom_target(first DEPENDS output-not-created)
add_custom_target(second DEPENDS output-created)
add_dependencies(second first)

In CMake 3.18 and lower, the Makefile generators put a copy of both custom commands in the Makefile for target second even though its dependency on target first ensures that the first custom command runs before the second. Running make second would cause the first custom command to run once in the first target and then again in the second target.

CMake 3.19 and above prefer to not duplicate custom commands in a target that are already generated in other targets on which the target depends (directly or indirectly). This policy provides compatibility for projects that have not been updated to expect the new behavior. In particular, projects that relied on the duplicate execution or that did not properly set the SYMBOLIC source file property may be affected.

The OLD behavior for this policy is to duplicate custom commands in dependent targets. The NEW behavior of this policy is to not duplicate custom commands in dependent targets.

This policy was introduced in CMake version 3.19. It may be set by cmake_policy() or cmake_minimum_required(). If it is not set, CMake does not warn, and uses OLD behavior.


The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.