This is sample code for a Roslyn analyzer and code fix as part of this series of posts which detail writing a custom analyzer and code fix.
Part 1: Roslyn Analyzer - explained
Part 2: Roslyn Analyzer - writing an analyzer
Part 3: Roslyn Analyzer - writing a code fix
Part 4: Roslyn Analyzer - testing an analyzer and code fix
Part 5: Roslyn Analyzer - tips and tricks