The right way to compare two strings in a case-insensitive manner is via a StringComparer/Comparison that specifies case-insensitivity. But there's are many cases where code is using ToLower() on each string and then comparing those for equality, e.g.

• https://grep.app/search?q=%5C.ToLower%5C%28%5C%29%20%3D%3D%20%5Cw%2B%5C.ToLower%5C%28%5C%29&regexp=true&case=true&filter[lang][0]=C%23
• https://grep.app/search?q=%5C.ToUpper%5C%28%5C%29%20%3D%3D%20%5Cw%2B%5C.ToUpper%5C%28&regexp=true&case=true&filter[lang][0]=C%23
• https://grep.app/search?q=%5C.ToLower%5C%28%5C%29%5C.Equals%5C%28%5Cw%2B%5C.ToLower%5C%28%5C%29&regexp=true&case=true&filter[lang][0]=C%23
• https://grep.app/search?q=%5C.ToUpper%5C%28%5C%29%5C.Equals%5C%28%5Cw%2B%5C.ToUpper%5C%28%5C%29&regexp=true&case=true&filter[lang][0]=C%23

We should write an analyzer that flags such uses and recommends fixing them to use Equals with the appropriate comparison.

This analyzer should cover ToUpper too even if the usage is low for that.

Such analyzers will help avoid the allocations caused by ToLower/ToUpper calls.

Performance rules Category
Severity = suggestion