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Record dependencies of a cast on other casts that it requires.

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When creating a cast that uses a conversion function, we've
historically allowed the input and result types to be
binary-compatible with the function's input and result types,
rather than necessarily being identical.  This means that the new
cast is logically dependent on the binary-compatible cast or casts
that it references: if those are defined by pg_cast entries, and you
try to restore the new cast without having defined them, it'll fail.
Hence, we should make pg_depend entries to record these dependencies
so that pg_dump knows that there is an ordering requirement.

This is not the only place where we allow such shortcuts; aggregate
functions for example are similarly lax, and in principle should gain
similar dependencies.  However, for now it seems sufficient to fix
the cast-versus-cast case, as pg_dump's other ordering heuristics
should keep it out of trouble for other object types.

Per report from David Turoň; thanks also to Robert Haas for
preliminary investigation.  I considered back-patching, but
seeing that this issue has existed for many years without
previous reports, it's not clear it's worth the trouble.
Moreover, back-patching wouldn't be enough to ensure that the
new pg_depend entries exist in existing databases anyway.

Discussion: https://postgr.es/m/OF0A160F3E.578B15D1-ONC12588DA.003E4857-C12588DA.0045A428@notes.linuxbox.cz
This commit is contained in:
Tom Lane
2022-10-17 14:02:05 -04:00
parent 797e313dc9
commit 8272749e8c
9 changed files with 111 additions and 9 deletions
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21
src/backend/parser/parse_coerce.c
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@ -2993,11 +2993,29 @@ IsPreferredType(TYPCATEGORY category, Oid type)
*/
bool
IsBinaryCoercible(Oid srctype, Oid targettype)
{
Oid castoid;
return IsBinaryCoercibleWithCast(srctype, targettype, &castoid);
}
/* IsBinaryCoercibleWithCast()
* Check if srctype is binary-coercible to targettype.
*
* This variant also returns the OID of the pg_cast entry if one is involved.
* *castoid is set to InvalidOid if no binary-coercible cast exists, or if
* there is a hard-wired rule for it rather than a pg_cast entry.
*/
bool
IsBinaryCoercibleWithCast(Oid srctype, Oid targettype,
Oid *castoid)
{
HeapTuple tuple;
Form_pg_cast castForm;
bool result;
*castoid = InvalidOid;
/* Fast path if same type */
if (srctype == targettype)
return true;
@ -3061,6 +3079,9 @@ IsBinaryCoercible(Oid srctype, Oid targettype)
result = (castForm->castmethod == COERCION_METHOD_BINARY &&
castForm->castcontext == COERCION_CODE_IMPLICIT);
if (result)
*castoid = castForm->oid;
ReleaseSysCache(tuple);
return result;