Re: Proposal: Make use of C99 designated initialisers fornulls/values arrays

On 10/2/19 11:02 AM, Tom Lane wrote:
> Mark Dilger <hornschnorter@gmail.com> writes:
>> On 10/2/19 8:46 AM, Tom Lane wrote:
>>> Right.  I think that in general it's bad practice for an initializer
>>> to not specify all fields/elements of the target.
> 
>> There are numerous locations in the code that raise warnings when
>> -Wmissing-field-initializers is handed to gcc.  See, for example,
>> src/backend/utils/adt/formatting.c where
>>     static const KeyWord NUM_keywords[]
>> is initialized, and the code comment above that disclaims the need to
>> initialize is_digit and date_mode.  Are you proposing cleaning up all
>> such incomplete initializations within the project?
> 
> Hmm.  Maybe it's worth doing as a code beautification effort, but
> I'm not volunteering.  At the same time, I wouldn't like to make a
> change like this, if it introduces dozens/hundreds of new cases.
> 
>> I understand that your INIT_ALL_ZEROS macro does nothing to change
>> whether -Wmissing-field-initializers would raise a warning.
> 
> Not sure --- the name of that option suggests that maybe it only
> complains about omitted *struct fields* not omitted *array elements*.


With gcc (Debian 8.3.0-6) 8.3.0

   int foo[6] = {0, 1, 2};

does not draw a warning when compiled with this flag.

> If it does complain, is there any way that we could extend the macro
> to annotate usages of it to suppress the warning?

Neither initializing a struct with {0} nor with INIT_ALL_ZEROS draws a 
warning either, with my gcc.  There are reports online that older 
versions of the compiler did, see

   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36750

but I don't have an older version to test with just now.

Note that initializing a multi-element struct with {1} does still draw a 
warning, and reading the thread above suggests that gcc made a specific 
effort to allow initialization to {0} to work without warning as a 
special case.

So your proposal for using INIT_ALL_ZEROS is probably good with 
sufficiently new compilers, and I'm generally in favor of the proposal, 
but I don't think the decree you propose can work unless somebody cleans 
up all these other cases that I indicated in my prior email.

(I'm sitting on a few patches until v12 goes out the door from some 
conversations with you several months ago, and perhaps I'll include a 
patch for this cleanup, too, when time comes for v13 patch sets to be 
submitted.  My past experience submitting patches shortly before a
release was that they get ignored.)

mark