Re: [PATCH] build: correct cppcheck-misra make rule

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.09.2022 15:50, Bertrand Marquis wrote:
>> On 9 Sep 2022, at 14:41, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> It has been bothering me for a while that I made a bad suggestion during
> 
> This is not a sentence for a commit message.

How else should I express the motivation for the change?

>> review: Having cppcheck-misra.json depend on cppcheck-misra.txt does not
>> properly address the multiple targets problem. If cppcheck-misra.json
>> is deleted from the build tree but cppcheck-misra.txt is still there,
>> nothing will re-generate cppcheck-misra.json.
>>
>> With GNU make 4.3 or newer we could use the &: grouped target separator,
>> but since we support older make as well we need to use some other
>> mechanism. Convert the rule to a pattern one (with "cppcheck"
>> arbitrarily chosen as the stem), thus making known to make that both
>> files are created by a single command invocation. Since, as a result,
>> the JSON file is now "intermediate" from make's perspective, prevent it
>> being deleted again by making it a prereq of .PRECIOUS.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> I've not been able to spot where / how cppcheck-misra.txt is used. If
>> it's indeed unused, a perhaps better alternative would be to convert the
>> original rule to specify cppcheck-misra.json as (the only) target. One
>> might then even consider using "-o /dev/null" instead of producing an
>> unused *.txt file.
> 
> Txt file is used by cppcheck to give a text description of the rule.
> If you look inside the json content you will see it mentioned.

Oh, that's properly hidden then.

>> --- a/xen/Makefile
>> +++ b/xen/Makefile
>> @@ -746,11 +746,9 @@ cppcheck-version:
>> # documentation file. Also generate a json file with the right arguments for
>> # cppcheck in json format including the list of rules to ignore.
>> #
>> -cppcheck-misra.txt: $(XEN_ROOT)/docs/misra/rules.rst 
>> $(srctree)/tools/convert_misra_doc.py
>> -    $(Q)$(PYTHON) $(srctree)/tools/convert_misra_doc.py -i $< -o $@ -j 
>> $(@:.txt=.json)
>> -
>> -# convert_misra_doc is generating both files.
>> -cppcheck-misra.json: cppcheck-misra.txt
>> +.PRECIOUS: %-misra.json
>> +%-misra.txt %-misra.json: $(XEN_ROOT)/docs/misra/rules.rst 
>> $(srctree)/tools/convert_misra_doc.py
>> +    $(Q)$(PYTHON) $(srctree)/tools/convert_misra_doc.py -i $< -o 
>> $*-misra.txt -j $*-misra.json
> 
> As far as I know, this is not saying to make that both files are generated by 
> this rule,
> but that this rule can generate both files so nothing is telling make here 
> that calling
> it once is enough I think.

As said in the description - it specifically has this effect. We're
using this elsewhere already, see e.g. tools/libs/light/Makefile
generating three headers and a C file all in one go. Iirc this is
also explicitly described in make documentation (and contrasted to
the different behavior for non-pattern rules).

Jan