[CLion] CLion always prompts "This file does not belong to any project target xxx" solution

Reference: In IntelliJ, How Do I Fix “These Files Do Not Belong to the Project”?

When using CLion to write c++, when the top of the file prompts "This file does not belong to any project target xxx", you can do the following:

1. If it is a header file: If the header file is not referenced by other files, this prompt will be displayed, so the header file needs to be referenced elsewhere.
2. If it is a source file: If the source file is not added to the CMakeLists.txt file, this prompt will be displayed, so you need to add this file to the CMakeList, then delete the cmake cache and re-Reload CMake Project .
3. If it is a header/source file newly added to the project: The reason is that the new file is not added to the build command in the cmake cache, and the solution is the same as 1 and 2.

But in my project, there is a problem that does not belong to any of the above, but the above file still prompts "This file does not belong to any project target xxx". After some research, I solved it like this:

Menu bar File -> Invalidate Caches… -> Invalidate and Restart.

CLion no longer prompts after restarting.