Add new flag to format_type_extended() to get NULL for undefined type

If a type scanned is undefined, type format routines have two behaviors
depending on if FORMAT_TYPE_ALLOW_INVALID is used by the caller or not:
- Issue a cache lookup error
- Return an undefined type name "???", "???[]" or "-"

The current interface is not really helpful for callers willing to
format properly a type name, but still make sure that the type is
defined as there could be types matching the strings generated when
looking for an undefined type, even if that should not be a problem in
practice.  In order to counter that, add a new flag called
FORMAT_TYPE_INVALID_AS_NULL that returns a NULL result instead of "???
or "-" which does not generate an error.  This flag will be used in a
follow-up patch improving the set of SQL functions showing information
for object addresses when it comes to undefined objects.

Author: Michael Paquier
Reviewed-by: Aleksander Alekseev, Dmitry Dolgov, Daniel Gustafsson,
Álvaro Herrera
Discussion: https://postgr.es/m/CAB7nPqSZxrSmdHK-rny7z8mi=EAFXJ5J-0RbzDw6aus=wB5azQ@mail.gmail.com

1 files changed, 1 insertions, 0 deletions

diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index f8595642da9..3ca5e938f8f 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -113,6 +113,7 @@ extern Datum numeric_float8_no_overflow(PG_FUNCTION_ARGS);
 #define FORMAT_TYPE_TYPEMOD_GIVEN	0x01	/* typemod defined by caller */
 #define FORMAT_TYPE_ALLOW_INVALID	0x02	/* allow invalid types */
 #define FORMAT_TYPE_FORCE_QUALIFY	0x04	/* force qualification of type */
+#define FORMAT_TYPE_INVALID_AS_NULL	0x08	/* NULL if undefined */
 extern char *format_type_extended(Oid type_oid, int32 typemod, bits16 flags);
 
 extern char *format_type_be(Oid type_oid);