Project created while working on Slicer issue "4595: multiple rules generate slicer (ninja error)". See https://issues.slicer.org/view.php?id=4595

CMakeLists.txt

cmake_minimum_required(VERSION 3.12)

project(Test LANGUAGES CXX)

# launcher executable
set(CTKAppLauncher_EXECUTABLE ${CMAKE_CURRENT_BINARY_DIR}/fake_launcher_executable)
file(WRITE ${CTKAppLauncher_EXECUTABLE} "")

# application and executable name
set(application_target "AwesomeApp")
set(application_name "Awesome")
set(executable_name "Awesome")
#if(NOT APPLE
#  set(executable_name ${executable_name}App-real) # Setting a different filename "workaround" the problem
#endif()

#
# target type
#
set(target_type)
if(APPLE)
  set(target_type MACOSX_BUNDLE)
endif()

#
# target built in "<root>/bin"
#
add_executable(${application_target} ${target_type} main.cpp)
set_target_properties(${application_target} PROPERTIES
  OUTPUT_NAME ${executable_name}
  RUNTIME_OUTPUT_DIRECTORY  ${CMAKE_CURRENT_BINARY_DIR}/bin
  )
message(STATUS "Setting ${application_name} executable name to '${executable_name}${CMAKE_EXECUTABLE_SUFFIX}'")

#
# install target
#
if(NOT APPLE)
  set(install_destination_args RUNTIME DESTINATION "bin")
else()
  set(install_destination_args BUNDLE DESTINATION ".")
endif()

install(
  TARGETS ${application_target}
  ${install_destination_args}
  COMPONENT Runtime
  )

#
# configured launcher in "<root>"
#
set(configured_launcher_executable "${CMAKE_CURRENT_BINARY_DIR}/${application_name}")

set(configure_launcher_command
  ${CMAKE_COMMAND} -E copy ${CTKAppLauncher_EXECUTABLE} ${configured_launcher_executable}
  )

set(configure_launcher_comment
  "Configuring application launcher: ${application_name}"
  )

# Create command to copy the launcher
if(CMAKE_VERSION VERSION_GREATER 3.12.0)
  message(STATUS "Adding Configure${application_name}Launcher command as regular regular build rule")
  add_custom_command(
    DEPENDS
      ${CTKAppLauncher_EXECUTABLE}
    OUTPUT
      ${configured_launcher_executable}
    COMMAND
      ${configure_launcher_command}
    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
    COMMENT
      ${configure_launcher_comment}
    )

  add_custom_target(Configure${application_name}Launcher ALL
    DEPENDS
      ${application_target}
      ${CTKAppLauncher_EXECUTABLE}
      ${configured_launcher_executable}
    )

else()
  # Workaround issue https://issues.slicer.org/view.php?id=4595
  message(STATUS "Adding Configure${application_name}Launcher command as a POST_BUILD event")
  add_custom_target(Configure${application_name}Launcher ALL
    DEPENDS
      ${CTKAppLauncher_EXECUTABLE}
      ${application_target}
    COMMAND
      ${configure_launcher_command}
    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
    COMMENT
      ${configure_launcher_comment}
    )

endif()

#
# side-effect: When using Ninja generator, it automatically adds an alias target for executables.
#              This should only happen when there are no conflicting target,
#              Proposed fix: https://gitlab.kitware.com/jcfr/cmake/commits/ninja-generator-do-not-add-alias-matching-custom-command-output
#

#
# Display path of the "real" application
#
get_target_property(application_output_dir ${application_target} RUNTIME_OUTPUT_DIRECTORY)
set(application_build_subdir "")
if(APPLE)
  get_target_property(_is_bundle ${application_target} MACOSX_BUNDLE)
  if(_is_bundle)
    set(application_build_subdir "${application_name}.app/Contents/MacOS/")
  endif()
endif()
set(real_executable "${application_output_dir}/${application_build_subdir}${executable_name}${CMAKE_EXECUTABLE_SUFFIX}")
message(STATUS "Setting ${application_name} real_executable to '${real_executable}'")

main.cpp

#include <iostream>
int main(int, char*[])
{
  std::cout << "Hello" << std::endl;
  return 0;
}

The issue originally occurred when building Slicer using Ninja generator on macOS.

This small project allows to reproduce the issue linux.

In a nutshell, the project:

• adds an executable target named AwesomeApp that creates the executable <root>/bin/Awesome
• adds a custom target and associated command to configure the launcher <root>/Awesome

failure using ninja

Configuring the project using kitware/ninja currently returns:

$ git clone git://gist.github.com/7e342d8ff786b82ff81873a96f66a292.git test-ninja && \
   mkdir test-ninja-build && \
   cd test-ninja-build && \
   cmake -G Ninja ../test-ninja && \
   ninja
ninja: error: build.ninja:103: multiple rules generate Awesome [-w dupbuild=err]

details of build.ninja

[...]

# Custom command for Awesome

build Awesome: CUSTOM_COMMAND CTKAppLauncher-0.1.24-linux-amd64/bin/CTKAppLauncher
  COMMAND = cd /tmp/test-ninja-build && /home/jcfr/Software/cmake-3.12.0-Linux-x86_64/bin/cmake -E copy /tmp/test-ninja-build/CTKAppLauncher-0.1.24-linux-amd64/bin/CTKAppLauncher /tmp/test-ninja-build/Awesome
  DESC = Configuring application launcher: Awesome
  restat = 1
# =============================================================================
# Target aliases.

build Awesome: phony bin/Awesome
build AwesomeApp: phony bin/Awesome

[...]

This phony rule is problematic:

build Awesome: phony bin/Awesome

workaround

On linux, we can easily address the problem setting the name of the executable to be <root>/bin/AwesomeApp-real instead of <root>/bin/Awesome

That said, this workaround is less preferable on macOS where the executable is of type MACOSX_BUNDLE and generated as <root>/bin/Awesome.app/Contents/MacOS/Awesome. Indeed, in that case we really want the name Awesome.app (instead of AwesomeApp-real.app) because the application will be fixed up and no launcher is provided to the user.

success using makefile

$ git clone git://gist.github.com/7e342d8ff786b82ff81873a96f66a292.git test-cmake && \
   mkdir test-cmake-build && \
   cd test-cmake-build && \
   cmake ../test-cmake && \
   make

Another work-around?

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2c71dc2..03114d2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@

-cmake_minimum_required(VERSION 3.12)
+cmake_minimum_required(VERSION 3.11)

 project(Test LANGUAGES CXX)

@@ -37,19 +37,6 @@ message(STATUS "Setting ${application_name} executable name to '${executable_nam
 #
 set(configured_launcher_executable "${CMAKE_CURRENT_BINARY_DIR}/${application_name}")

-# Create command to copy the launcher
-add_custom_command(
-  DEPENDS
-    ${CTKAppLauncher_EXECUTABLE}
-  OUTPUT
-    ${configured_launcher_executable}
-  COMMAND
-    ${CMAKE_COMMAND} -E copy ${CTKAppLauncher_EXECUTABLE} ${configured_launcher_executable}
-  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-  COMMENT
-    "Configuring application launcher: ${application_name}"
-  )
-
 #
 # side-effect: When using Ninja generator, it automatically adds an alias target if one of the
 #              dependency has a filename matching the name of an existing target.
@@ -60,5 +47,15 @@ add_custom_command(
 add_custom_target(Configure${application_name}Launcher ALL
   DEPENDS
     ${CTKAppLauncher_EXECUTABLE}
-    ${configured_launcher_executable}
+  )
+
+# Create command to copy the launcher
+add_custom_command(TARGET Configure${application_name}Launcher POST_BUILD
+  DEPENDS
+    ${CTKAppLauncher_EXECUTABLE}
+  COMMAND
+    ${CMAKE_COMMAND} -E copy ${CTKAppLauncher_EXECUTABLE} ${configured_launcher_executable}
+  WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+  COMMENT
+    "Configuring application launcher: ${application_name}"
   )