Remove complaints about COLLATE clauses in partition bound values.

transformPartitionBoundValue went out of its way to do the wrong
thing: there is no reason to complain about a non-matching COLLATE
clause in a partition boundary expression.  We're coercing the
bound expression to the target column type as though by an
implicit assignment, and the rules for implicit assignment say
that collations can be implicitly converted.

What we *do* need to do, and the code is not doing, is apply
assign_expr_collations() to the bound expression.  While this is
merely a definition disagreement, that is a bug that needs to be
back-patched, so I'll commit it separately.

Discussion: https://postgr.es/m/CAJV4CdrZ5mKuaEsRSbLf2URQ3h6iMtKD=hik8MaF5WwdmC9uZw@mail.gmail.com

src/backend/parser/parse_utilcmd.c

@@ -4183,50 +4183,6 @@ transformPartitionBoundValue(ParseState *pstate, Node *val,
 	 */
 	Assert(!contain_var_clause(value));
 
-	/*
-	 * Check that the input expression's collation is compatible with one
-	 * specified for the parent's partition key (partcollation).  Don't throw
-	 * an error if it's the default collation which we'll replace with the
-	 * parent's collation anyway.
-	 */
-	if (IsA(value, CollateExpr))
-	{
-		Oid			exprCollOid = exprCollation(value);
-
-		/*
-		 * Check we have a collation iff it is a collatable type.  The only
-		 * expected failures here are (1) COLLATE applied to a noncollatable
-		 * type, or (2) partition bound expression had an unresolved
-		 * collation.  But we might as well code this to be a complete
-		 * consistency check.
-		 */
-		if (type_is_collatable(colType))
-		{
-			if (!OidIsValid(exprCollOid))
-				ereport(ERROR,
-						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("could not determine which collation to use for partition bound expression"),
-						 errhint("Use the COLLATE clause to set the collation explicitly.")));
-		}
-		else
-		{
-			if (OidIsValid(exprCollOid))
-				ereport(ERROR,
-						(errcode(ERRCODE_DATATYPE_MISMATCH),
-						 errmsg("collations are not supported by type %s",
-								format_type_be(colType))));
-		}
-
-		if (OidIsValid(exprCollOid) &&
-			exprCollOid != DEFAULT_COLLATION_OID &&
-			exprCollOid != partCollation)
-			ereport(ERROR,
-					(errcode(ERRCODE_DATATYPE_MISMATCH),
-					 errmsg("collation of partition bound value for column \"%s\" does not match partition key collation \"%s\"",
-							colName, get_collation_name(partCollation)),
-					 parser_errposition(pstate, exprLocation(value))));
-	}
-
 	/*
 	 * Coerce to the correct type.  This might cause an explicit coercion step
 	 * to be added on top of the expression, which must be evaluated before

src/test/regress/expected/create_table.out

@@ -652,8 +652,6 @@ CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN (genera
 ERROR:  set-returning functions are not allowed in partition bound
 LINE 1: ...expr_fail PARTITION OF list_parted FOR VALUES IN (generate_s...
                                                              ^
-CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN ('1' collate "POSIX");
-ERROR:  collations are not supported by type integer
 CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN ((1+1) collate "POSIX");
 ERROR:  collations are not supported by type integer
 LINE 1: ...ail PARTITION OF list_parted FOR VALUES IN ((1+1) collate "P...
@@ -1026,28 +1024,28 @@ create table parted_collate_must_match1 partition of parted_collate_must_match
 create table parted_collate_must_match2 partition of parted_collate_must_match
   (b collate "POSIX") for values from ('m') to ('z');
 drop table parted_collate_must_match;
--- check that specifying incompatible collations for partition bound
--- expressions fails promptly
+-- check that non-matching collations for partition bound
+-- expressions are coerced to the right collation
 create table test_part_coll_posix (a text) partition by range (a collate "POSIX");
--- fail
+-- ok, collation is implicitly coerced
 create table test_part_coll partition of test_part_coll_posix for values from ('a' collate "C") to ('g');
-ERROR:  collation of partition bound value for column "a" does not match partition key collation "POSIX"
-LINE 1: ...artition of test_part_coll_posix for values from ('a' collat...
-                                                             ^
--- ok
-create table test_part_coll partition of test_part_coll_posix for values from ('a' collate "POSIX") to ('g');
 -- ok
 create table test_part_coll2 partition of test_part_coll_posix for values from ('g') to ('m');
--- using a cast expression uses the target type's default collation
--- fail
+-- ok, collation is implicitly coerced
 create table test_part_coll_cast partition of test_part_coll_posix for values from (name 'm' collate "C") to ('s');
-ERROR:  collation of partition bound value for column "a" does not match partition key collation "POSIX"
-LINE 1: ...ion of test_part_coll_posix for values from (name 'm' collat...
-                                                             ^
--- ok
-create table test_part_coll_cast partition of test_part_coll_posix for values from (name 'm' collate "POSIX") to ('s');
 -- ok; partition collation silently overrides the default collation of type 'name'
 create table test_part_coll_cast2 partition of test_part_coll_posix for values from (name 's') to ('z');
+\d+ test_part_coll_posix
+                    Partitioned table "public.test_part_coll_posix"
+ Column | Type | Collation | Nullable | Default | Storage  | Stats target | Description 
+--------+------+-----------+----------+---------+----------+--------------+-------------
+ a      | text |           |          |         | extended |              | 
+Partition key: RANGE (a COLLATE "POSIX")
+Partitions: test_part_coll FOR VALUES FROM ('a') TO ('g'),
+            test_part_coll2 FOR VALUES FROM ('g') TO ('m'),
+            test_part_coll_cast FOR VALUES FROM ('m') TO ('s'),
+            test_part_coll_cast2 FOR VALUES FROM ('s') TO ('z')
+
 drop table test_part_coll_posix;
 -- Partition bound in describe output
 \d+ part_b

src/test/regress/sql/create_table.sql

@@ -549,7 +549,6 @@ CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN (sum(so
 CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN (sum(1));
 CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN ((select 1));
 CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN (generate_series(4, 6));
-CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN ('1' collate "POSIX");
 CREATE TABLE part_bogus_expr_fail PARTITION OF list_parted FOR VALUES IN ((1+1) collate "POSIX");
 
 -- syntax does not allow empty list of values for list partitions
@@ -813,26 +812,21 @@ create table parted_collate_must_match2 partition of parted_collate_must_match
   (b collate "POSIX") for values from ('m') to ('z');
 drop table parted_collate_must_match;
 
--- check that specifying incompatible collations for partition bound
--- expressions fails promptly
+-- check that non-matching collations for partition bound
+-- expressions are coerced to the right collation
 
 create table test_part_coll_posix (a text) partition by range (a collate "POSIX");
--- fail
+-- ok, collation is implicitly coerced
 create table test_part_coll partition of test_part_coll_posix for values from ('a' collate "C") to ('g');
 -- ok
-create table test_part_coll partition of test_part_coll_posix for values from ('a' collate "POSIX") to ('g');
--- ok
 create table test_part_coll2 partition of test_part_coll_posix for values from ('g') to ('m');
-
--- using a cast expression uses the target type's default collation
-
--- fail
+-- ok, collation is implicitly coerced
 create table test_part_coll_cast partition of test_part_coll_posix for values from (name 'm' collate "C") to ('s');
--- ok
-create table test_part_coll_cast partition of test_part_coll_posix for values from (name 'm' collate "POSIX") to ('s');
 -- ok; partition collation silently overrides the default collation of type 'name'
 create table test_part_coll_cast2 partition of test_part_coll_posix for values from (name 's') to ('z');
 
+\d+ test_part_coll_posix
+
 drop table test_part_coll_posix;
 
 -- Partition bound in describe output