pragma Unreferenced (LOCAL_NAME {, LOCAL_NAME});
pragma Unreferenced (library_unit_NAME {, library_unit_NAME});
This pragma signals that the entities whose names are listed are deliberately not referenced in the current source unit after the occurrence of the pragma. This suppresses warnings about the entities being unreferenced, and in addition a warning will be generated if one of these entities is in fact subsequently referenced in the same unit as the pragma (or in the corresponding body, or one of its subunits).
This is particularly useful for clearly signaling that a particular parameter is not referenced in some particular subprogram implementation and that this is deliberate. It can also be useful in the case of objects declared only for their initialization or finalization side effects.
If LOCAL_NAME identifies more than one matching homonym in the current scope, then the entity most recently declared is the one to which the pragma applies. Note that in the case of accept formals, the pragma Unreferenced may appear immediately after the keyword do which allows the indication of whether or not accept formals are referenced or not to be given individually for each accept statement.
The left hand side of an assignment does not count as a reference for the purpose of this pragma. Thus it is fine to assign to an entity for which pragma Unreferenced is given.
Note that if a warning is desired for all calls to a given subprogram, regardless of whether they occur in the same unit as the subprogram declaration, then this pragma should not be used (calls from another unit would not be flagged); pragma Obsolescent can be used instead for this purpose, see Pragma Obsolescent.
The second form of pragma Unreferenced is used within a context clause. In this case the arguments must be unit names of units previously mentioned in with clauses (similar to the usage of pragma Elaborate_All. The effect is to suppress warnings about unreferenced units and unreferenced entities within these units.
For the variable case, warnings are never given for unreferenced variables whose name contains one of the substrings DISCARD, DUMMY, IGNORE, JUNK, UNUSED in any casing. Such names are typically to be used in cases where such warnings are expected. Thus it is never necessary to use pragma Unreferenced for such variables, though it is harmless to do so.