The jetbrains IDEs hav some very useful features falling into this category, these come to my mind immediately: - Making variables, functions,... grey if they'

The jetbrains IDEs hav some very useful features falling into this category, these come to my mind immediately: - Making variables, functions,... grey if they're not used - Temporarily coloring variables + their usages when the cursor is on one - Showing wiggled red underlines for syntax errors Especially the unused code feature is wonderful.