This pragma has the same syntax and semantics as pragma Source_File_Name. It is only allowed as a stand-alone configuration pragma. It cannot appear after a Pragma Source_File_Name, and most importantly, once pragma Source_File_Name_Project appears, no further Source_File_Name pragmas are allowed.
The intention is that Source_File_Name_Project pragmas are always generated by the Project Manager in a manner consistent with the naming specified in a project file, and when naming is controlled in this manner, it is not permissible to attempt to modify this naming scheme using Source_File_Name or Source_File_Name_Project pragmas (which would not be known to the project manager).