add_custom_command does not re-run on failure

Question

In CMake, I would like to use add_custom_command(... POST_BUILD ...) with a COMMAND that might fail.

Observation

1. Running make will fail the first time, because the exit code of add_custom_command( ... COMMAND exit 1) is not 0. --> This is what I would expect.
2. Running make a second time will pass, because the command specified in the add_custom_command will not be run again. --> This is not what I want. I would want make to fail until the custom command works.

Minimium Failing Example

project(Foo)
cmake_minimum_required(VERSION 3.2)


# Create main.cc
##include <iostream>
#
#int main() {
#  std::cout << "Hello, World!" << std::endl;
#}
add_executable(main main.cc)

add_custom_command(TARGET main POST_BUILD
          COMMAND exit 1  # In the real example, I am changing capabilities of the resulting binary with /sbin/setcap, which might fail.
          COMMENT "Doing stuff."
          )

Question

1. How can I resolve this issue?
2. Is this intended behavior of CMake?

One solution

I am aware that I can create a custom command that is not a POST_BUILD but instead outputs a file TARGET.passed on success. However, I would like to avoid this. Because POST_BUILD seems the most appropriate usage here. (I am changing capabilities of the resulting file.)

Answer 1

This used to be a bug in CMake.

It was fixed in the following commit:

commit 4adf1dad2a6e462364bae81030c928599d11c24f
Author: Brad King <brad.king@kitware.com>
Date:   Mon Mar 30 16:32:26 2015 -0400

    Makefile: Tell GNU make to delete rule outputs on error (#15474)

    Add .DELETE_ON_ERROR to the "build.make" files that contain the actual
    build rules that generate files.  This tells GNU make to delete the
    output of a rule if the recipe modifies the output but returns failure.
    This is particularly useful for custom commands that use shell
    redirection to produce a file.

    Do not add .DELETE_ON_ERROR for Borland or Watcom make tools because
    they may not tolerate it and would not honor it anyway.  Other make
    tools that do not understand .DELETE_ON_ERROR will not be hurt.

    Suggested-by: Andrey Vihrov <andrey.vihrov@gmail.com>

The earliest release with that fix was CMake 3.3.0.

Workaround

• Create an additional output target that depends on the custom command having successfully run. (Below this is called main.done)
• Switch the custom command from being a POST_BUILD on a TARGET, to being a standalone command. Thus make it OUTPUT a file (main.intermediate_step below).
• Use the option to run a second COMMAND to create said file using touch.

Code:

project(Foo)
cmake_minimum_required(VERSION 3.2)


# Create main.cc
##include <iostream>
#
#int main() {
#  std::cout << "Hello, World!" << std::endl;
#}
add_executable(main main.cc)

add_custom_command(TARGET main POST_BUILD
          COMMAND exit 1  # In the real example, I am changing capabilities of the resulting binary with /sbin/setcap, which might fail.
          COMMENT "Doing stuff."
          )

add_custom_command(OUTPUT main.intermediate_step
                  COMMAND  exit 1  # In the real example, I am changing capabilities of the resulting binary with /sbin/setcap, which might fail.
                  COMMAND touch main_setcap.passed
                  DEPENDS main
                  COMMENT "Doing stuff."
)
add_custom_target(main.done ALL DEPENDS main.intermediate_step)

Note: make main will not run the custom command. Use make main.done for that. make and make all will work as intended.