Use version check instead of bumping minimum cmake version

Signed-off-by: Anthony Welte <[email protected]>

Author: TonyWelte

rosidl_typesupport_c/cmake/rosidl_typesupport_c_generate_interfaces.cmake

@@ -83,12 +83,18 @@ rosidl_write_generator_arguments(
 # the search will prefer /usr/bin/python3 over /usr/bin/python3.11.  And that
 # latter functionality is only available in CMake 3.20 or later, so we need
 # at least that version.
-cmake_minimum_required(VERSION 3.27) # Required by option DEPENDS_EXPLICIT_ONLY of add_custom_command
+cmake_minimum_required(VERSION 3.20)
 cmake_policy(SET CMP0094 NEW)
 set(Python3_FIND_UNVERSIONED_NAMES FIRST)
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
+if(${CMAKE_VERSION} VERSION_GREATER_EQUAL 3.27)
+  set(_dep_explicit_only DEPENDS_EXPLICIT_ONLY)
+else()
+  set(_dep_explicit_only "")
+endif()
+
 get_used_typesupports(typesupports "rosidl_typesupport_c")
 add_custom_command(
   OUTPUT ${_generated_sources}
@@ -99,7 +105,7 @@ add_custom_command(
   DEPENDS ${target_dependencies}
   COMMENT "Generating C type support dispatch for ROS interfaces"
   VERBATIM
-  DEPENDS_EXPLICIT_ONLY
+  ${_dep_explicit_only}
 )
 
 set(_target_suffix "__rosidl_typesupport_c")

rosidl_typesupport_cpp/cmake/rosidl_typesupport_cpp_generate_interfaces.cmake

@@ -80,12 +80,18 @@ rosidl_write_generator_arguments(
 # the search will prefer /usr/bin/python3 over /usr/bin/python3.11.  And that
 # latter functionality is only available in CMake 3.20 or later, so we need
 # at least that version.
-cmake_minimum_required(VERSION 3.27) # Required by option DEPENDS_EXPLICIT_ONLY of add_custom_command
+cmake_minimum_required(VERSION 3.20)
 cmake_policy(SET CMP0094 NEW)
 set(Python3_FIND_UNVERSIONED_NAMES FIRST)
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
+if(${CMAKE_VERSION} VERSION_GREATER_EQUAL 3.27)
+  set(_dep_explicit_only DEPENDS_EXPLICIT_ONLY)
+else()
+  set(_dep_explicit_only "")
+endif()
+
 get_used_typesupports(typesupports "rosidl_typesupport_cpp")
 add_custom_command(
   OUTPUT ${_generated_sources}
@@ -96,7 +102,7 @@ add_custom_command(
   DEPENDS ${target_dependencies}
   COMMENT "Generating C++ type support dispatch for ROS interfaces"
   VERBATIM
-  DEPENDS_EXPLICIT_ONLY
+  ${_dep_explicit_only}
 )
 
 set(_target_suffix "__rosidl_typesupport_cpp")