[fpc-devel] Minor debate with ISO standard on case blocks

[thaddy]

On 2019-07-31 08:26, Marco Borsari via fpc-devel wrote:
> On Wed, 31 Jul 2019 01:26:23 +0200
> Martok <listbox at martoks-place.de> wrote:
> 
>> Of course, if you wanted a run-time error you would need to insert a 
>> run-time
>> check, and 'some people' seemed to be hell-bent on saving these 2 
>> cycles at any
>> cost.
>> 
>> The patch to switch from option a1) to a2) would be straightforward, 
>> fix 32079
>> and insert a default otherwise clause that raises a RunError in -Miso. 
>> But the
>> question is again, does Freepascal actually aim to be compliant with 
>> anything,
>> or just have a compatible syntax and do its own thing from there?
> 
> It seems to me that the problem of a lack of correspondence in a case
> statement list should be of the same level of attention of the index
> limits of an array, except there is no memory corruption risk. The
> solution could be to insert a run time check in presence of the
> switch {$R+}, if the latter is allowed in iso mode.
> 
> Greetings, Marco Borsari
No, that is not allowed in the context of the standards, but the 
compiler solves that already earlier in the code path and if the code is 
compiled with {$rangechecks on} an out of bounds will be detected. What 
needs to be detected if all *used* labels are within the confines of the 
used ordinal, but a selector without label should throw an error.
In the case of my patch it behaves like extended pascal mode and throws 
a run-time error in that case. That is debatable in some cases, because 
if the selector has no label and the compiler can resolve that at 
compile time it should in my opinion and how I read ISO 10206 throw a 
compile-time error. See my remarks and test code.
Maybe you can evaluate those conclusions I made.