cmake_policy(PUSH)
cmake_policy(SET CMP0053 OLD)
set(FOO "${OLD_WARN_FROM_NORMAL_CMAKE_FILE_INSIDE_BRACES}")
set(FOO "@OLD_WARN_FROM_NORMAL_CMAKE_FILE_IN_ATS@")
string(CONFIGURE "\${OLD_WARN_FROM_STRING_CONFIGURE_INSIDE_BRACES}" OUT1)
file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/file1.in "\@OLD_WARN_FROM_CONFIGURE_FILE_INSIDE_AT\@")
configure_file(${CMAKE_CURRENT_BINARY_DIR}/file1.in file1.out)
string(CONFIGURE "\@OLD_WARN_FROM_STRING_CONFIGURE_INSIDE_AT\@" OUT2)
cmake_policy(POP)

cmake_policy(PUSH)
cmake_policy(SET CMP0053 NEW)
set(FOO "${NEW_WARN_FROM_NORMAL_CMAKE_FILE_INSIDE_BRACES}")
string(CONFIGURE "\${NEW_WARN_FROM_STRING_CONFIGURE_INSIDE_BRACES}" OUT3)
file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/file2.in "\@NEW_WARN_FROM_CONFIGURE_FILE_INSIDE_AT\@")
configure_file(${CMAKE_CURRENT_BINARY_DIR}/file2.in file2.out)
string(CONFIGURE "@NEW_WARN_FROM_STRING_CONFIGURE_INSIDE_AT@" OUT4)
cmake_policy(POP)