fix-alter-table-some-more.patch

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index cb2c5e1..83dc6df 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -10508,9 +10508,6 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	SysScanDesc scan;
 	HeapTuple	depTup;
 	ObjectAddress address;
-	ListCell   *lc;
-	ListCell   *prev;
-	ListCell   *next;
 
 	/*
 	 * Clear all the missing values if we're rewriting the table, since this
@@ -10603,11 +10600,6 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	 * performed all the individual ALTER TYPE operations.  We have to save
 	 * the info before executing ALTER TYPE, though, else the deparser will
 	 * get confused.
-	 *
-	 * There could be multiple entries for the same object, so we must check
-	 * to ensure we process each one only once.  Note: we assume that an index
-	 * that implements a constraint will not show a direct dependency on the
-	 * column.
 	 */
 	depRel = table_open(DependRelationId, RowExclusiveLock);
 
@@ -10650,19 +10642,21 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 						relKind == RELKIND_PARTITIONED_INDEX)
 					{
 						/*
-						 * Indexes that are directly dependent on the table
-						 * might be regular indexes or constraint indexes.
-						 * Constraint indexes typically have only indirect
-						 * dependencies; but there are exceptions, notably
-						 * partial exclusion constraints.  Hence we must check
-						 * whether the index depends on any constraint that's
-						 * due to be rebuilt, which we'll do below after we've
-						 * found all such constraints.
+						 * This de-duplication check is critical for two
+						 * independent reasons: we mustn't try to create the
+						 * same index twice, and if an index depends on more
+						 * than one column whose type is to be altered, we
+						 * must capture its definition string before applying
+						 * any of the column type changes.
 						 */
 						Assert(foundObject.objectSubId == 0);
-						tab->changedIndexOids =
-							list_append_unique_oid(tab->changedIndexOids,
-												   foundObject.objectId);
+						if (!list_member_oid(tab->changedIndexOids, foundObject.objectId))
+						{
+							tab->changedIndexOids = lappend_oid(tab->changedIndexOids,
+																foundObject.objectId);
+							tab->changedIndexDefs = lappend(tab->changedIndexDefs,
+															pg_get_indexdef_string(foundObject.objectId));
+						}
 					}
 					else if (relKind == RELKIND_SEQUENCE)
 					{
@@ -10697,6 +10691,12 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 				}
 
 			case OCLASS_CONSTRAINT:
+
+				/*
+				 * As with indexes, de-duplication is critical, and it's
+				 * needed because the same constraint could depend on multiple
+				 * target columns.
+				 */
 				Assert(foundObject.objectSubId == 0);
 				if (!list_member_oid(tab->changedConstraintOids,
 									 foundObject.objectId))
@@ -10829,41 +10829,6 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	systable_endscan(scan);
 
 	/*
-	 * Check the collected index OIDs to see which ones belong to the
-	 * constraint(s) of the table, and drop those from the list of indexes
-	 * that we need to process; rebuilding the constraints will handle them.
-	 */
-	prev = NULL;
-	for (lc = list_head(tab->changedIndexOids); lc; lc = next)
-	{
-		Oid			indexoid = lfirst_oid(lc);
-		Oid			conoid;
-
-		next = lnext(lc);
-
-		conoid = get_index_constraint(indexoid);
-		if (OidIsValid(conoid) &&
-			list_member_oid(tab->changedConstraintOids, conoid))
-			tab->changedIndexOids = list_delete_cell(tab->changedIndexOids,
-													 lc, prev);
-		else
-			prev = lc;
-	}
-
-	/*
-	 * Now collect the definitions of the indexes that must be rebuilt.  (We
-	 * could merge this into the previous loop, but it'd be more complicated
-	 * for little gain.)
-	 */
-	foreach(lc, tab->changedIndexOids)
-	{
-		Oid			indexoid = lfirst_oid(lc);
-
-		tab->changedIndexDefs = lappend(tab->changedIndexDefs,
-										pg_get_indexdef_string(indexoid));
-	}
-
-	/*
 	 * Now scan for dependencies of this column on other things.  The only
 	 * thing we should find is the dependency on the column datatype, which we
 	 * want to remove, possibly a collation dependency, and dependencies on
@@ -11242,8 +11207,25 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 			def_item, tab->changedIndexDefs)
 	{
 		Oid			oldId = lfirst_oid(oid_item);
+		Oid			conoid;
 		Oid			relid;
 
+		/*
+		 * We must check each index to see if it belongs to a constraint that
+		 * we already processed above.  Typically this check does not fire
+		 * because constraint indexes normally have only dependencies on their
+		 * constraint, and thus would not have been found by the dependency
+		 * scan in ATExecAlterColumnType.  But it's possible for such an index
+		 * to also have direct dependencies on the table, for example with a
+		 * partial exclusion constraint.  In that case we'd have list entries
+		 * for both the index and the constraint, and we must disregard the
+		 * one for the index.
+		 */
+		conoid = get_index_constraint(oldId);
+		if (OidIsValid(conoid) &&
+			list_member_oid(tab->changedConstraintOids, conoid))
+			continue;
+
 		relid = IndexGetRelation(oldId, false);
 		ATPostAlterTypeParse(oldId, relid, InvalidOid,
 							 (char *) lfirst(def_item),
diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index c845a16..01ba41c 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -1906,6 +1906,10 @@ alter table anothertab
   add exclude using btree (f3 with =);
 alter table anothertab
   add exclude using btree (f4 with =) where (f4 is not null);
+alter table anothertab
+  add unique(f3,f4);
+create index on anothertab(f2,f3);
+create unique index on anothertab(f4);
 \d anothertab
              Table "public.anothertab"
  Column |  Type   | Collation | Nullable | Default 
@@ -1917,6 +1921,9 @@ alter table anothertab
 Indexes:
     "anothertab_pkey" PRIMARY KEY, btree (f1)
     "anothertab_f2_key" UNIQUE CONSTRAINT, btree (f2)
+    "anothertab_f3_f4_key" UNIQUE CONSTRAINT, btree (f3, f4)
+    "anothertab_f4_idx" UNIQUE, btree (f4)
+    "anothertab_f2_f3_idx" btree (f2, f3)
     "anothertab_f3_excl" EXCLUDE USING btree (f3 WITH =)
     "anothertab_f4_excl" EXCLUDE USING btree (f4 WITH =) WHERE (f4 IS NOT NULL)
 
@@ -1936,6 +1943,9 @@ alter table anothertab
 Indexes:
     "anothertab_pkey" PRIMARY KEY, btree (f1)
     "anothertab_f2_key" UNIQUE CONSTRAINT, btree (f2)
+    "anothertab_f3_f4_key" UNIQUE CONSTRAINT, btree (f3, f4)
+    "anothertab_f4_idx" UNIQUE, btree (f4)
+    "anothertab_f2_f3_idx" btree (f2, f3)
     "anothertab_f3_excl" EXCLUDE USING btree (f3 WITH =)
     "anothertab_f4_excl" EXCLUDE USING btree (f4 WITH =) WHERE (f4 IS NOT NULL)
 
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 8c8b627..95fa1ce 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -1323,6 +1323,10 @@ alter table anothertab
   add exclude using btree (f3 with =);
 alter table anothertab
   add exclude using btree (f4 with =) where (f4 is not null);
+alter table anothertab
+  add unique(f3,f4);
+create index on anothertab(f2,f3);
+create unique index on anothertab(f4);
 
 \d anothertab
 alter table anothertab alter column f1 type bigint;