Deep Dive: Semantic Duplicate Detection with AST Analysis - How AI Keeps Rewriting Your Logic

You've just asked your AI assistant to add email validation to your new signup form. It writes this: function validateEmail ( email : string ): boolean { return email . includes ( ' @ ' ) && email . includes ( ' . ' ); } Simple enough. But here's the problem: this exact logic—checking for '@' and '.'—already exists in four other places in your codebase, just written differently: // In src/utils/validators.ts const isValidEmail = ( e ) => e . indexOf ( ' @ ' ) !== - 1 && e . indexOf ( ' . ' ) !== - 1 ; // In src/api/auth.ts if ( user . email . match ( /@/ ) && user . email . match ( / \. / )) { /* ... */ } // In src/components/EmailForm.tsx const checkEmail = ( val ) => val . split ( '' ). includes ( ' @ ' ) && val . split ( '' ). includes ( ' . ' ); // In src/services/user-service.ts return email . search ( ' @ ' ) >= 0 && email . search ( ' . ' ) >= 0 ; Your AI didn't see these patterns. Why? Because they look different syntactically, even though they're semantically identical. This i