I wrote:
> Ah. No, that would still work after the change. The case that I'm
> proposing to break is using function-ish notation to invoke a cast
> from a composite type to some other type whose name you use as if it
> were a function. Even there, if you've created such a cast following
> the usual convention of naming the cast function after the target type,
> it'll still act the same. It's just the built-in I/O-based casts that
> will stop working this way (for lack of a matching underlying function).
Here's a proposed patch, sans documentation as yet.
regards, tom lane
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index b50bce448728280f63c695a688c004bd15bf84cf..9bb100e0c1e83c63b554f65300c03afed563373a 100644
*** a/src/backend/parser/parse_func.c
--- b/src/backend/parser/parse_func.c
*************** func_get_detail(List *funcname,
*** 985,992 ****
* can't write "foo[] (something)" as a function call. In theory
* someone might want to invoke it as "_foo (something)" but we have
* never supported that historically, so we can insist that people
! * write it as a normal cast instead. Lack of historical support is
! * also the reason for not considering composite-type casts here.
*
* NB: it's important that this code does not exceed what coerce_type
* can do, because the caller will try to apply coerce_type if we
--- 985,997 ----
* can't write "foo[] (something)" as a function call. In theory
* someone might want to invoke it as "_foo (something)" but we have
* never supported that historically, so we can insist that people
! * write it as a normal cast instead.
! *
! * We also reject the specific case of COERCEVIAIO for a composite
! * source type and a string-category target type. This is a case that
! * find_coercion_pathway() allows by default, but experience has shown
! * that it's too commonly invoked by mistake. So, again, insist that
! * people use cast syntax if they want to do that.
*
* NB: it's important that this code does not exceed what coerce_type
* can do, because the caller will try to apply coerce_type if we
*************** func_get_detail(List *funcname,
*** 1017,1024 ****
cpathtype = find_coercion_pathway(targetType, sourceType,
COERCION_EXPLICIT,
&cfuncid);
! iscoercion = (cpathtype == COERCION_PATH_RELABELTYPE ||
! cpathtype == COERCION_PATH_COERCEVIAIO);
}
if (iscoercion)
--- 1022,1044 ----
cpathtype = find_coercion_pathway(targetType, sourceType,
COERCION_EXPLICIT,
&cfuncid);
! switch (cpathtype)
! {
! case COERCION_PATH_RELABELTYPE:
! iscoercion = true;
! break;
! case COERCION_PATH_COERCEVIAIO:
! if ((sourceType == RECORDOID ||
! ISCOMPLEX(sourceType)) &&
! TypeCategory(targetType) == TYPCATEGORY_STRING)
! iscoercion = false;
! else
! iscoercion = true;
! break;
! default:
! iscoercion = false;
! break;
! }
}
if (iscoercion)
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