How to revert a function definition in CMake? - cmake

Question

CMake allows masking any function like this
function(add_executable)
#...custom code, that may use _add_executable(${ARGN}) to call the original function
endfunction()
But it seems that once CMake parsed that function definition, it set in global CMake scope and nesting of function definitions is not supported:
function(echo)
message(STATUS "Original function")
endfunction()
echo() #Original function
function(nesting)
function(echo)
message(STATUS "Overwritten function")
# _echo() # Original function
endfunction()
echo() #Overwritten function
endfunction()
echo() #Still Overwritten function, expected Original function
It will also not work if you include the new definition, or even if you define it in CMakeLists added by add_subdirectory. Using macros also does not help:
macro(echo)
_echo(${ARGN})
endmacro(echo)
echo() #Still Overwritten function, but now even _echo() is overwritten
Is there any way to revert the old meaning of the function?

Answer 1

Here is one walkaround I found. It is not a true answer, but it works.
function(echo)
message(STATUS "Original function")
endfunction()
echo() #Original function
function(echo)
if(__ECHO_BEHAVIORAL_SWITCH)
message(STATUS "Overwritten function")
else()
_echo()
endif()
endfunction()
function(nesting)
set(__ECHO_BEHAVIORAL_SWITCH 1)
echo() #Overwritten function
endfunction()
nesting() #Overwritten function
echo() #Original function
It does not revert the definition of the function, but rather bounds the behaviour of the overwritten function to the external variable, that may be cached inside functions or add_subdirectory just like I expected.