Assign collations in partition bound expressions.

Failure to do this can result in errors during evaluation of
the bound expression, as illustrated by the new regression test.

Back-patch to v12 where the ability for partition bounds to be
expressions was added.

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

src/backend/parser/parse_utilcmd.c

@@ -4239,7 +4239,10 @@ transformPartitionBoundValue(ParseState *pstate, Node *val,
 
 	/* Simplify the expression, in case we had a coercion */
 	if (!IsA(value, Const))
+	{
+		assign_expr_collations(pstate, value);
 		value = (Node *) expression_planner((Expr *) value);
+	}
 
 	/*
 	 * transformExpr() should have already rejected column references,

src/test/regress/expected/create_table.out

@@ -986,6 +986,13 @@ DETAIL:  Failing row contains (1, null).
 Partition of: parted_notnull_inh_test FOR VALUES IN (1)
 
 drop table parted_notnull_inh_test;
+-- check that collations are assigned in partition bound expressions
+create table parted_boolean_col (a bool, b text) partition by list(a);
+create table parted_boolean_less partition of parted_boolean_col
+  for values in ('foo' < 'bar');
+create table parted_boolean_greater partition of parted_boolean_col
+  for values in ('foo' > 'bar');
+drop table parted_boolean_col;
 -- check for a conflicting COLLATE clause
 create table parted_collate_must_match (a text collate "C", b text collate "C")
   partition by range (a);

src/test/regress/sql/create_table.sql

@@ -802,6 +802,14 @@ insert into parted_notnull_inh_test (b) values (null);
 \d parted_notnull_inh_test1
 drop table parted_notnull_inh_test;
 
+-- check that collations are assigned in partition bound expressions
+create table parted_boolean_col (a bool, b text) partition by list(a);
+create table parted_boolean_less partition of parted_boolean_col
+  for values in ('foo' < 'bar');
+create table parted_boolean_greater partition of parted_boolean_col
+  for values in ('foo' > 'bar');
+drop table parted_boolean_col;
+
 -- check for a conflicting COLLATE clause
 create table parted_collate_must_match (a text collate "C", b text collate "C")
   partition by range (a);