Compile-Time Warnings

Oracle can now produce compile-time warnings when code is ambiguous or inefficient be setting the PLSQL_WARNINGS parameter at either instance or session level.The categories ALL, SEVERE, INFORMATIONAL and PERFORMANCE can be used to alter the type of warnings that are produced.

How to enable it?

ALTER SESSION SET PLSQL_WARNINGS='ENABLE:ALL';

Warning:

SP2-0804: Procedure created with compilation warnings

HTH:-)