list(INSERT): Empty elements discarded immediately in CMake v3.27

CMake v3.27 broke list handling of empty elements. It discards them similar to CMP0007=old, but immediately. The expected behavior is CMP0007=new, which does not seem to exist anymore.

Use cmake -P with this script to reproduce:

function(f)
    cmake_policy(SET CMP0007 ${ARGN})
    set(my_list "0;1;2;3;4")

    list(INSERT my_list 1 "")
    message(STATUS "${my_list}")

    list(INSERT my_list 4 ";")
    message(STATUS "${my_list}")

    list(INSERT my_list 0 "x")
    message(STATUS "${my_list}")
endfunction()

f(NEW)

#[[ v3.26.5 prints
-- 0;;1;2;3;4
-- 0;;1;2;;;3;4
-- x;0;;1;2;;;3;4
]]

#[[ v3.27.0 - v3.27.3 prints
-- 0;1;2;3;4
-- 0;1;2;3;4
-- x;0;1;2;3;4
]]

f(OLD)

#[[ v3.26.5 prints
-- 0;;1;2;3;4
-- 0;1;2;3;;;4
-- x;0;1;2;3;4
]]

#[[ v3.27.0 - v3.27.3 prints
-- 0;1;2;3;4
-- 0;1;2;3;4
-- x;0;1;2;3;4
]]

@marc.chevrier I guess this is related to the changes made for #24547 (closed)

Yes, this is related to this feature. This regression was introduced by !8401 (merged). Fixed in !8732 (merged).

mentioned in merge request !8732 (merged)

added triage:regression label

changed milestone to %3.27.4

changed title from Empty list elements discarded immediately in CMake v3.27 to list(INSERT): Empty elements discarded immediately in CMake v3.27

assigned to @marc.chevrier

closed with commit 45ed175f

mentioned in commit 45ed175f