Re: [BUGS] BUG #14849: jsonb_build_object doesn't like VARIADIC callsvery much

On Mon, Oct 23, 2017 at 7:03 AM, Michael Paquier
<michael.paquier@gmail.com> wrote:
>> Looks good otherwise.
>
> My set of diffs for funcapi.h are actually that:
>   * funcapi.h
>   *   Definitions for functions which return composite type and/or sets
> + *   or work on VARIADIC inputs.
> [...]
> +/*----------
> + * Support to ease writing of functions dealing with VARIADIC inputs
> + *----------
> + *
> + * This function extracts a set of argument values, types and NULL markers
> + * for a given input function. This returns a set of data:
> + * - **values includes the set of Datum values extracted.
> + * - **types the data type OID for each element.
> + * - **nulls tracks if an element is NULL.
> + *
> + * convert_unknown set to true enforces conversion of unknown input type
> + * unknown to text.
> + * variadic_start tracks the argument number of the function call where the
> + * VARIADIC set of arguments begins.
> + *
> + * The return result is the number of elements stored. In the event of a
> + * NULL input, then the caller of this function ought to generate a NULL
> + * object as final result, and in this case a result value of -1 is used
> + * to be able to make the difference between an empty array or object.
> + */
> +extern int extract_variadic_args(FunctionCallInfo fcinfo, int variadic_start,
> +                                bool convert_unknown, Datum **values,
> Oid **types,
> +                                bool **nulls);
>
> Got this bit as well:
>   * funcapi.c
>   *   Utility and convenience functions for fmgr functions that return
> - *   sets and/or composite types.
> + *   sets and/or composite types, or deal with VARIADIC inputs.
>   *

Okay, attached is what I think a fully implemented patch should look
like. On top of what Andrew has done, I added and reworked the
following:
- removed duplicate error handling.
- documented the function in funcapi.h and funcapi.c.
- Added a new section in funcapi.h to outline that this is for support
of VARIADIC inputs.
I have added a commit message as well. Hope this helps.

format, concat and potentially count_nulls could take advantage of
this new function, though refactoring is left for later. I am fine to
do the legwork on a different thread. Changing count_nulls would also
switch it to a o(n^2),  which is not cool either, so I think that it
could be left out. Still let's discuss that on another thread.
-- 
Michael

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