New in version 3.20.

Source file extensions must be explicit.

In CMake 3.19 and below, if a source file could not be found by the name specified, it would append a list of known extensions to the name to see if the file with the extension could be found. For example, this would allow the user to run:

add_executable(exe main)

and put main.c in the executable without specifying the extension.

Starting in CMake 3.20, CMake prefers all source files to have their extensions explicitly listed:

add_executable(exe main.c)

The OLD behavior for this policy is to implicitly append known extensions to source files if they can't be found. The NEW behavior of this policy is to not append known extensions and require them to be explicit.

This policy was introduced in CMake version 3.20. CMake version 3.23.20220523-g722a9a6 warns when the policy is not set and uses OLD behavior. Use the cmake_policy() command to set it to OLD or NEW explicitly.


The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.