When using the non-ANSI style, it is legal to have duplicate ports in the port list. However, such duplicate ports are often the result of a coding error and can cause unintended behavior. Duplicate ports are marked as warnings by Sigasi (rule 140).
module discouraged_code( a, a, b ); input a; output b; ... endmodule
This rule can be disabled for your project, or its severity and parameters can be modified in the project linting settings. Alternatively, it can be manually configured with the following template: