Fix infer_arbiter_indexes() to not assume resultRelation is 1.

infer_arbiter_indexes failed to renumber varnos in index expressions
or predicates that it got from the catalogs.  This escaped detection
up to now because the stored varnos in such trees will be 1, and an
INSERT's result relation is usually the first rangetable entry,
so that that was fine.  However, in cases such as inserting through
an updatable view, it's not fine, leading to failure to match the
expressions to the query with ensuing "there is no unique or exclusion
constraint matching the ON CONFLICT specification" errors.

Fix by copy-and-paste from get_relation_info().

Per bug #18502 from Michael Wang.  Back-patch to all supported
versions.

Discussion: https://postgr.es/m/18502-545b53f5b81e54e0@postgresql.org

src/backend/optimizer/util/plancat.c

@@ -667,6 +667,7 @@ infer_arbiter_indexes(PlannerInfo *root)
 	OnConflictExpr *onconflict = root->parse->onConflict;
 
 	/* Iteration state */
+	Index		varno;
 	RangeTblEntry *rte;
 	Relation	relation;
 	Oid			indexOidFromConstraint = InvalidOid;
@@ -695,7 +696,8 @@ infer_arbiter_indexes(PlannerInfo *root)
 	 * the rewriter or when expand_inherited_rtentry() added it to the query's
 	 * rangetable.
 	 */
-	rte = rt_fetch(root->parse->resultRelation, root->parse->rtable);
+	varno = root->parse->resultRelation;
+	rte = rt_fetch(varno, root->parse->rtable);
 
 	relation = table_open(rte->relid, NoLock);
 
@@ -829,6 +831,9 @@ infer_arbiter_indexes(PlannerInfo *root)
 
 		/* Expression attributes (if any) must match */
 		idxExprs = RelationGetIndexExpressions(idxRel);
+		if (idxExprs && varno != 1)
+			ChangeVarNodes((Node *) idxExprs, 1, varno, 0);
+
 		foreach(el, onconflict->arbiterElems)
 		{
 			InferenceElem *elem = (InferenceElem *) lfirst(el);
@@ -880,6 +885,8 @@ infer_arbiter_indexes(PlannerInfo *root)
 		 * CONFLICT's WHERE clause.
 		 */
 		predExprs = RelationGetIndexPredicate(idxRel);
+		if (predExprs && varno != 1)
+			ChangeVarNodes((Node *) predExprs, 1, varno, 0);
 
 		if (!predicate_implied_by(predExprs, (List *) onconflict->arbiterWhere, false))
 			goto next;

src/test/regress/expected/insert_conflict.out

@@ -2,6 +2,8 @@
 -- insert...on conflict do unique index inference
 --
 create table insertconflicttest(key int4, fruit text);
+-- These things should work through a view, as well
+create view insertconflictview as select * from insertconflicttest;
 --
 -- Test unique index inference with operator class specifications and
 -- named collations
@@ -43,6 +45,15 @@ explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on con
    ->  Result
 (4 rows)
 
+explain (costs off) insert into insertconflictview values(0, 'Crowberry') on conflict (lower(fruit), key, lower(fruit), key) do nothing;
+                   QUERY PLAN                    
+-------------------------------------------------
+ Insert on insertconflicttest
+   Conflict Resolution: NOTHING
+   Conflict Arbiter Indexes: both_index_expr_key
+   ->  Result
+(4 rows)
+
 explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on conflict (key, fruit) do update set fruit = excluded.fruit
   where exists (select 1 from insertconflicttest ii where ii.key = excluded.key);
                                   QUERY PLAN                                   
@@ -374,6 +385,7 @@ create unique index partial_key_index on insertconflicttest(key) where fruit lik
 -- Succeeds
 insert into insertconflicttest values (23, 'Blackberry') on conflict (key) where fruit like '%berry' do update set fruit = excluded.fruit;
 insert into insertconflicttest as t values (23, 'Blackberry') on conflict (key) where fruit like '%berry' and t.fruit = 'inconsequential' do nothing;
+insert into insertconflictview as t values (23, 'Blackberry') on conflict (key) where fruit like '%berry' and t.fruit = 'inconsequential' do nothing;
 -- fails
 insert into insertconflicttest values (23, 'Blackberry') on conflict (key) do update set fruit = excluded.fruit;
 ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification
@@ -439,6 +451,7 @@ explain (costs off) insert into insertconflicttest as i values (23, 'Avocado') o
 
 drop index plain;
 -- Cleanup
+drop view insertconflictview;
 drop table insertconflicttest;
 --
 -- Verify that EXCLUDED does not allow system column references. These

src/test/regress/sql/insert_conflict.sql

@@ -3,6 +3,9 @@
 --
 create table insertconflicttest(key int4, fruit text);
 
+-- These things should work through a view, as well
+create view insertconflictview as select * from insertconflicttest;
+
 --
 -- Test unique index inference with operator class specifications and
 -- named collations
@@ -20,6 +23,7 @@ explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on con
 explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on conflict (key, fruit) do nothing;
 explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on conflict (fruit, key, fruit, key) do nothing;
 explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on conflict (lower(fruit), key, lower(fruit), key) do nothing;
+explain (costs off) insert into insertconflictview values(0, 'Crowberry') on conflict (lower(fruit), key, lower(fruit), key) do nothing;
 explain (costs off) insert into insertconflicttest values(0, 'Crowberry') on conflict (key, fruit) do update set fruit = excluded.fruit
   where exists (select 1 from insertconflicttest ii where ii.key = excluded.key);
 -- Neither collation nor operator class specifications are required --
@@ -215,6 +219,7 @@ create unique index partial_key_index on insertconflicttest(key) where fruit lik
 -- Succeeds
 insert into insertconflicttest values (23, 'Blackberry') on conflict (key) where fruit like '%berry' do update set fruit = excluded.fruit;
 insert into insertconflicttest as t values (23, 'Blackberry') on conflict (key) where fruit like '%berry' and t.fruit = 'inconsequential' do nothing;
+insert into insertconflictview as t values (23, 'Blackberry') on conflict (key) where fruit like '%berry' and t.fruit = 'inconsequential' do nothing;
 
 -- fails
 insert into insertconflicttest values (23, 'Blackberry') on conflict (key) do update set fruit = excluded.fruit;
@@ -247,6 +252,7 @@ explain (costs off) insert into insertconflicttest as i values (23, 'Avocado') o
 drop index plain;
 
 -- Cleanup
+drop view insertconflictview;
 drop table insertconflicttest;