Re: [XEN PATCH] automation/eclair: add deviations for MISRA C:2012 Rule 16.4

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.04.2024 17:52, Federico Serafini wrote:
> On 23/04/24 12:26, Jan Beulich wrote:
>> On 23.04.2024 12:02, Federico Serafini wrote:
>>> --- a/docs/misra/deviations.rst
>>> +++ b/docs/misra/deviations.rst
>>> @@ -302,6 +302,19 @@ Deviations related to MISRA C:2012 Rules:
>>>          leave such files as is.
>>>        - Tagged as `deliberate` for ECLAIR.
>>>   
>>> +   * - R16.4
>>> +     - Switch statements having a controlling expression of enum type
>>> +       deliberately do not have a default case: gcc -Wall enables -Wswitch
>>> +       which warns (and breaks the build as we use -Werror) if one of the 
>>> enum
>>> +       labels is missing from the switch.
>>> +     - Tagged as `deliberate` for ECLAIR.
>>> +
>>> +   * - R16.4
>>> +     - A switch statement with a single switch clause and no default label 
>>> may
>>> +       be used in place of an equivalent if statement if it is considered 
>>> to
>>> +       improve readability."
> 
> (I placed Rule 16.4 before Rule 16.3.
> I will propose a new version with the correct ordering.)
> 
>>
>> First a terminology related comment here: I'm afraid "switch clause" can be
>> interpreted multiple ways, when I think we want to leave no room for
>> interpretation here. It's not even clear to me whether
>>
>>      switch ( x )
>>      {
>>      case 1: case 2: case 3: case 4:
>>          ...
>>          break;
>>      }
>>
>> would be covered by the deviation, or whether the multiple case labels
>> wouldn't already be too much.
> 
> The MISRA C document, within Rule 16.1 ("A switch statement shall be
> well-formed") defines the syntax rules that can be used to define a
> "well formed" switch statement.
> When I say "switch clause", I refer to the same entity the MISRA
> document refers to in the definition of such syntax rules.
> In the example above, we have a single switch clause with multiple
> labels and no default label: this is a violation of Rule 16.4
> ("Every `switch' statement shall have a `default' label") which will
> be covered by the deviation.
> Do you think inserting the example in rules.rst or deviations.rst could
> be useful?

No, I don't think there should be examples in those documents. But those
documents should also not (blindly) rely on terminology in the Misra
spec, as not everyone has access to that (licensed copies had to be
obtained for quite a few of us).

Jan