[fpc-devel] "Case statement does not handle all possible cases" Warning

Jonas Maebe jonas at freepascal.org
Sat May 18 14:03:23 CEST 2019

On 18/05/2019 13:30, J. Gareth Moreton wrote:

> So it looks like this new warning has appeared as part of the data flow 
> analysis of -O4.

The case-completeness warning is not related to any optimization level, 
nor to the data flow analysis mentioned in the other thread.

>   The thing is, I personally have a problem with this 
> being a warning, because there's nothing inherently wrong with not 
> covering every case branch or omitting an else block (especially if one 
> isn't needed).  Adding "else ;" everywhere seems to just cause bloat.

The question is whether or not an else block is needed or not (or 
perhaps even superfluous). When I adapted the compiler code to compile 
warning-free with this new option, about 2/3 of the cases got an empty 
else-block and 1/3 got either an internalerror or extra case blocks to 
handle options that were not handled previously, but that should have 
been handled. I don't think that's a bad haul. There were also a number 
of case-statements that handled all possible options and yet still 
contained an else block (so the else-block got removed).

However, it is absolutely true that this is not an issue in all cases. 
If you do not wish to see such warnings at all, you can always suppress 
them using -vm6060 (warning numbers can be discovered with the -vq 
command line options).

For information on the background of this warning, see 

> Still, code style aside, can I suggest the warning be downgraded into a 
> hint? Warnings should indicate the possibility of unstable code due to 
> uninitialised values, for example, and DFA should be able to detect that 
> anyway as a separate warning (e.g. if a case block doesn't initialise an 
> output value in all of its branches).

This warning can detect errors that cannot be found by DFA, because they 
may not be related to initialising a variable (but e.g. to modifying an 
already initialised variable, or to outputting something).


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