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

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

1 files changed, 21 insertions, 0 deletions

diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index c4e958e4aa8..60908111c82 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -2994,10 +2994,28 @@ 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;