PHPStorm allows to mark a folder as "Excluded" (Go to Project view, right-click on a folder and choose "Mark Directory as... Excluded". Then, all the files in that folder will be ignored by the PHPStorm when it looks for functions, constants, etc. So, for example, if you have an older versions of a library, in "archive" folder, you can exclude it, and Code Inspection will not refer to those older method definitions, constants, etc.
But what if you need to exclude just a single file? The only way I found was to mark it as a plain text:
It's particularly useful for WordPress projects: those two files
- with no parameters or bodies. PHPStorm finds them, considers no params and a void return and issues useless inspection errors.
There is an alternative solution, suggested by Slava Abakumov: add the file(s) to the Settings->Editor->File Types->Ignore...
The drawback is that the file disappears completely from the Project view, and even by typing its name, you won't be able to find it. Ignored completely. This can be quite inconvenient if you want to ignore a file, but still be able to edit it.