Fix ruleutils.c for domain-over-array cases, too.

Further investigation shows that ruleutils isn't quite up to speed either
for cases where we have a domain-over-array: it needs to be prepared to
look past a CoerceToDomain at the top level of field and element
assignments, else it decompiles them incorrectly.  Potentially this would
result in failure to dump/reload a rule, if it looked like the one in the
new test case.  (I also added a test for EXPLAIN; that output isn't broken,
but clearly we need more test coverage here.)

Like commit b1cb32fb6, this bug is reachable in cases we already support,
so back-patch all the way.

src/backend/utils/adt/ruleutils.c

@@ -8634,12 +8634,17 @@ get_opclass_name(Oid opclass, Oid actual_datatype,
  * We strip any top-level FieldStore or assignment ArrayRef nodes that
  * appear in the input, and return the subexpression that's to be assigned.
  * If printit is true, we also print out the appropriate decoration for the
- * base column name (that the caller just printed).
+ * base column name (that the caller just printed).  We might also need to
+ * strip CoerceToDomain nodes, but only ones that appear above assignment
+ * nodes.
+ *
+ * Returns the subexpression that's to be assigned.
  */
 static Node *
 processIndirection(Node *node, deparse_context *context, bool printit)
 {
 	StringInfo	buf = context->buf;
+	CoerceToDomain *cdomain = NULL;
 
 	for (;;)
 	{
@@ -8689,10 +8694,28 @@ processIndirection(Node *node, deparse_context *context, bool printit)
 			 */
 			node = (Node *) aref->refassgnexpr;
 		}
+		else if (IsA(node, CoerceToDomain))
+		{
+			cdomain = (CoerceToDomain *) node;
+			/* If it's an explicit domain coercion, we're done */
+			if (cdomain->coercionformat != COERCE_IMPLICIT_CAST)
+				break;
+			/* Tentatively descend past the CoerceToDomain */
+			node = (Node *) cdomain->arg;
+		}
 		else
 			break;
 	}
 
+	/*
+	 * If we descended past a CoerceToDomain whose argument turned out not to
+	 * be a FieldStore or array assignment, back up to the CoerceToDomain.
+	 * (This is not enough to be fully correct if there are nested implicit
+	 * CoerceToDomains, but such cases shouldn't ever occur.)
+	 */
+	if (cdomain && node == (Node *) cdomain->arg)
+		node = (Node *) cdomain;
+
 	return node;
 }
 

src/test/regress/expected/domain.out

@@ -266,20 +266,48 @@ insert into dcomptable (d1[1].r, d1[1].i) values(100, 99);  -- fail
 ERROR:  value for domain dcomptypea violates check constraint "c1"
 update dcomptable set d1[1].r = d1[1].r + 1 where d1[1].i > 0;  -- fail
 ERROR:  value for domain dcomptypea violates check constraint "c1"
-update dcomptable set d1[1].r = d1[1].r - 1 where d1[1].i > 0;
+update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+  where d1[1].i > 0;
 select * from dcomptable;
          d1         
 --------------------
  {"(11,)","(,)"}
  {"(99,)"}
- {"(1,2)","(,)"}
+ {"(1,3)","(,)"}
- {"(3,4)","(6,5)"}
+ {"(3,5)","(6,5)"}
- {"(7,8)","(10,9)"}
+ {"(7,9)","(10,9)"}
- {"(9,10)","(,)"}
+ {"(9,11)","(,)"}
- {"(0,2)"}
+ {"(0,3)"}
- {"(98,100)"}
+ {"(98,101)"}
 (8 rows)
 
+explain (verbose, costs off)
+  update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+    where d1[1].i > 0;
+                                                 QUERY PLAN                                                 
+------------------------------------------------------------------------------------------------------------
+ Update on public.dcomptable
+   ->  Seq Scan on public.dcomptable
+         Output: (d1[1].r := (d1[1].r - 1::double precision))[1].i := (d1[1].i + 1::double precision), ctid
+         Filter: (dcomptable.d1[1].i > 0::double precision)
+(4 rows)
+
+create rule silly as on delete to dcomptable do instead
+  update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+    where d1[1].i > 0;
+\d+ dcomptable
+                        Table "public.dcomptable"
+ Column |    Type    | Modifiers | Storage  | Stats target | Description 
+--------+------------+-----------+----------+--------------+-------------
+ d1     | dcomptypea |           | extended |              | 
+Indexes:
+    "dcomptable_d1_key" UNIQUE CONSTRAINT, btree (d1)
+Rules:
+    silly AS
+    ON DELETE TO dcomptable DO INSTEAD  UPDATE dcomptable SET d1[1].r = dcomptable.d1[1].r - 1::double precision, d1[1].i = dcomptable.d1[1].i + 1::double precision
+  WHERE dcomptable.d1[1].i > 0::double precision
+Has OIDs: no
+
 drop table dcomptable;
 drop type comptype cascade;
 NOTICE:  drop cascades to type dcomptypea

src/test/regress/sql/domain.sql

@@ -150,9 +150,18 @@ insert into dcomptable (d1[1].r) values(99);
 insert into dcomptable (d1[1].r, d1[1].i) values(99, 100);
 insert into dcomptable (d1[1].r, d1[1].i) values(100, 99);  -- fail
 update dcomptable set d1[1].r = d1[1].r + 1 where d1[1].i > 0;  -- fail
-update dcomptable set d1[1].r = d1[1].r - 1 where d1[1].i > 0;
+update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+  where d1[1].i > 0;
 select * from dcomptable;
 
+explain (verbose, costs off)
+  update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+    where d1[1].i > 0;
+create rule silly as on delete to dcomptable do instead
+  update dcomptable set d1[1].r = d1[1].r - 1, d1[1].i = d1[1].i + 1
+    where d1[1].i > 0;
+\d+ dcomptable
+
 drop table dcomptable;
 drop type comptype cascade;