SQL/JSON: Some fixes to JsonBehavior expression casting

1. Remove the special case handling when casting the JsonBehavior
   expressions to types with typmod, like 86d33987 did for the casting
   of SQL/JSON constructor functions.

2. Fix casting for fixed-length character and bit string types by
   using assignment-level casts.  This is again similar to what
   86d33987 did, but for ON ERROR / EMPTY expressions.

3. Use runtime coercion for the boolean ON ERROR constants so that
   using fixed-length character string types, for example, for an
   EXISTS column doesn't cause a "value too long for type
   character(n)" when the parser tries to coerce the default ON ERROR
   value "false" to that type, that is, even when clause is not
   specified.

4. Simplify the conditions of when to use runtime coercion vs
   creating the cast expression in the parser itself.  jsonb-valued
   expressions are now always coerced at runtime and boolean
   expressions too if the target type is a string type for the
   reasons mentioned above.

New tests are from a patch that Jian He posted.  Outputs of some
existing tests change because the coercion now happens at runtime
instead of at parse time.

Reported-by: Jian He <jian.universality@gmail.com>
Author: Jian He <jian.universality@gmail.com>
Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

1 files changed, 15 insertions, 1 deletions

diff --git a/src/test/regress/sql/sqljson_queryfuncs.sql b/src/test/regress/sql/sqljson_queryfuncs.sql
index e9005d3d4eb..21ff7787a28 100644
--- a/src/test/regress/sql/sqljson_queryfuncs.sql
+++ b/src/test/regress/sql/sqljson_queryfuncs.sql
@@ -472,7 +472,8 @@ SELECT JSON_EXISTS(jsonb '1', '$' DEFAULT 1 ON ERROR);
 SELECT JSON_VALUE(jsonb '1', '$' EMPTY ON ERROR);
 SELECT JSON_QUERY(jsonb '1', '$' TRUE ON ERROR);
 
--- Test implicit coercion domain over fixed-legth type specified in RETURNING
+-- Test implicit coercion to a domain over fixed-length type specified in
+-- RETURNING
 CREATE DOMAIN queryfuncs_char2 AS char(2);
 CREATE DOMAIN queryfuncs_char2_chk AS char(2) CHECK (VALUE NOT IN ('12'));
 SELECT JSON_QUERY(jsonb '123', '$' RETURNING queryfuncs_char2 ERROR ON ERROR);
@@ -484,3 +485,16 @@ SELECT JSON_VALUE(jsonb '123', '$' RETURNING queryfuncs_char2 DEFAULT 1 ON ERROR
 SELECT JSON_VALUE(jsonb '123', '$' RETURNING queryfuncs_char2_chk ERROR ON ERROR);
 SELECT JSON_VALUE(jsonb '123', '$' RETURNING queryfuncs_char2_chk DEFAULT 1 ON ERROR);
 DROP DOMAIN queryfuncs_char2, queryfuncs_char2_chk;
+
+-- Test coercion to domain over another fixed-length type of the ON ERROR /
+-- EMPTY expressions.  Ask user to cast the DEFAULT expression explicitly if
+-- automatic casting cannot be done, for example, from int to bit(2).
+CREATE DOMAIN queryfuncs_d_varbit3 AS varbit(3) CHECK (VALUE <> '01');
+SELECT JSON_VALUE(jsonb '1234', '$' RETURNING queryfuncs_d_varbit3  DEFAULT '111111' ON ERROR);
+SELECT JSON_VALUE(jsonb '1234', '$' RETURNING queryfuncs_d_varbit3  DEFAULT '010' ON ERROR);
+SELECT JSON_VALUE(jsonb '1234', '$' RETURNING queryfuncs_d_varbit3  DEFAULT '01' ON ERROR);
+SELECT JSON_VALUE(jsonb '"111"', '$'  RETURNING bit(2) ERROR ON ERROR);
+SELECT JSON_VALUE(jsonb '1234', '$' RETURNING bit(3)  DEFAULT 1 ON ERROR);
+SELECT JSON_VALUE(jsonb '1234', '$' RETURNING bit(3)  DEFAULT 1::bit(3) ON ERROR);
+SELECT JSON_VALUE(jsonb '"111"', '$.a'  RETURNING bit(3) DEFAULT '1111' ON EMPTY);
+DROP DOMAIN queryfuncs_d_varbit3;