This error is triggered by calls to regex-accepting methods with invalid string literals. These calls would cause a PatternSyntaxException at runtime.

We deliberately do not check java.util.regex.Pattern#compile as many of its users are deliberately testing the regex compiler or using a vacuously true regex.

"." is also discouraged, as it is a valid regex but is easy to mistake for "\\.". Instead of e.g. str.replaceAll(".", "x"), prefer Strings.repeat("x", str.length()) or CharMatcher.ANY.replaceFrom(str, "x").