Re: MergeAttributes type (mod) conflict error detail

Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> writes:
> I wonder if the following error detail text could say more than it does
> currently for the following rather artificial example case:

> CREATE TABLE p1(a char(3));
> CREATE TABLE p2(a char(2));

> CREATE TABLE c(d int) INHERITS (p1, p2);
> NOTICE: merging multiple inherited definitions of column "a"
> ERROR: inherited column "a" has a type conflict
> DETAIL: character versus character

> Any specific reason why it doesn't spell out typmods in the above detail
> message?

I agree this could stand to be improved. There are probably a couple of
reasons why this code is like it is:

* We did not use to have format_type_with_typemod(), only
format_type_be(). That's easily changed now of course.

* There's a rough policy in the parser to prefer TypeNameToString
when complaining about a TypeName input, rather than reconstructing
the type name from the OID. The reason for this is that we'd rather
complain about the type name as entered, not the canonical type name
--- for example, if the user typed "float8" it might be a bit confusing
if the parser then complains about "double precision".

I'm not entirely sure though that that argument should be applied
to this particular case, because the other type referred to will
certainly get displayed in canonical form.

So we could either apply your patch as written, or we could replace
only the format_type_be calls with format_type_with_typemod, and
then fix TypeNameToString so that it will show the typmod if any.
(We'd need to consider whether that behavior is OK for all callers.)

Even if we decide this particular case is best handled by presenting
canonical type names on both sides, maybe it would be wise to look
into whether TypeNameToString should be changed for other callers.

regards, tom lane