If a case statement contains all the possible choices (usually in an
enumerated datatype), you can safely remove the when others clause.
Sigasi Visual HDL warns about this:
Unexpected ‘others’ choice, case statement covers all choices explicitly
case bits is
when "00" => -- code
when "01" => -- code
when "10" => -- code
when "11" => -- code
when others => -- never reached: all cases are covered
end case;
There is some debate on this coding rule. However, the vast majority of
synthesis tools do not take the others into account if all choices are
enumerated. If the synthesis tool is set up to generate fault-tolerant
hardware, the fallback state is the same as the reset state (for most
synthesis tools). Check the manual of your synthesis tools and run some
experiments.
For more information, see VHDL case statements can do without the “others”.
If you still prefer to always have an others choice for case statements, the validation can be configured to Always require 'others' choice. When configured this way, there will be warnings on all case statements that do not have an others choice, even if that choice would be redundant.
Rule Configuration
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:
13/severity/${path}={error|warning|info|ignore}
13/params/style/${path}={disallow_redundant_others_choices|always_require_others_choice}