HEADER_FILE_ONLY

Is this source file only a header file.

A property on a source file that indicates if the source file is a header file with no associated implementation. This is set automatically based on the file extension and is used by CMake to determine if certain dependency information should be computed.

© 2000–2019 Kitware, Inc. and Contributors
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.7/prop_sf/HEADER_FILE_ONLY.html