SQL/JSON: Improve error-handling of JsonBehavior expressions

Instead of returning a NULL when the JsonBehavior expression value
could not be coerced to the RETURNING type, throw the error message
informing the user that it is the JsonBehavior expression that caused
the error with the actual coercion error message shown in its DETAIL
line.

Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

2 files changed, 8 insertions, 20 deletions

diff --git a/src/test/regress/expected/sqljson_jsontable.out b/src/test/regress/expected/sqljson_jsontable.out
index 19817b4be8c..fcad9cc0289 100644
--- a/src/test/regress/expected/sqljson_jsontable.out
+++ b/src/test/regress/expected/sqljson_jsontable.out
@@ -227,11 +227,8 @@ SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
 
 SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
     COLUMNS (js1 jsonb_test_domain PATH '$.a2' DEFAULT 'foo'::jsonb_test_domain ON EMPTY));
- js1 
------
- 
-(1 row)
-
+ERROR:  could not coerce ON EMPTY expression (DEFAULT) to the RETURNING type
+DETAIL:  value for domain jsonb_test_domain violates check constraint "jsonb_test_domain_check"
 SELECT * FROM JSON_TABLE(jsonb '{"d1": "H"}', '$'
     COLUMNS (js1 jsonb_test_domain PATH '$.a2' DEFAULT 'foo1'::jsonb_test_domain ON EMPTY));
  js1  
diff --git a/src/test/regress/expected/sqljson_queryfuncs.out b/src/test/regress/expected/sqljson_queryfuncs.out
index ec8caee91c7..ab045e13590 100644
--- a/src/test/regress/expected/sqljson_queryfuncs.out
+++ b/src/test/regress/expected/sqljson_queryfuncs.out
@@ -313,11 +313,8 @@ SELECT JSON_VALUE(jsonb '"2017-02-20"', '$' RETURNING date) + 9;
 -- Test NULL checks execution in domain types
 CREATE DOMAIN sqljsonb_int_not_null AS int NOT NULL;
 SELECT JSON_VALUE(jsonb 'null', '$' RETURNING sqljsonb_int_not_null);
- json_value 
-------------
-           
-(1 row)
-
+ERROR:  could not coerce ON ERROR expression (NULL) to the RETURNING type
+DETAIL:  domain sqljsonb_int_not_null does not allow null values
 SELECT JSON_VALUE(jsonb 'null', '$' RETURNING sqljsonb_int_not_null ERROR ON ERROR);
 ERROR:  domain sqljsonb_int_not_null does not allow null values
 SELECT JSON_VALUE(jsonb 'null', '$' RETURNING sqljsonb_int_not_null DEFAULT 2 ON EMPTY ERROR ON ERROR);
@@ -1035,11 +1032,8 @@ SELECT JSON_QUERY(jsonb '{"a": 1}', '$.a' RETURNING sqljsonb_int_not_null);
 (1 row)
 
 SELECT JSON_QUERY(jsonb '{"a": 1}', '$.b' RETURNING sqljsonb_int_not_null);
- json_query 
-------------
-           
-(1 row)
-
+ERROR:  could not coerce ON EMPTY expression (NULL) to the RETURNING type
+DETAIL:  domain sqljsonb_int_not_null does not allow null values
 SELECT JSON_QUERY(jsonb '{"a": 1}', '$.b' RETURNING sqljsonb_int_not_null ERROR ON EMPTY ERROR ON ERROR);
 ERROR:  no SQL/JSON item found for specified path
 -- Test timestamptz passing and output
@@ -1232,11 +1226,8 @@ DROP TABLE test_jsonb_mutability;
 DROP FUNCTION ret_setint;
 CREATE DOMAIN queryfuncs_test_domain AS text CHECK (value <> 'foo');
 SELECT JSON_VALUE(jsonb '{"d1": "H"}', '$.a2' RETURNING queryfuncs_test_domain DEFAULT 'foo'::queryfuncs_test_domain ON EMPTY);
- json_value 
-------------
- 
-(1 row)
-
+ERROR:  could not coerce ON EMPTY expression (DEFAULT) to the RETURNING type
+DETAIL:  value for domain queryfuncs_test_domain violates check constraint "queryfuncs_test_domain_check"
 SELECT JSON_VALUE(jsonb '{"d1": "H"}', '$.a2' RETURNING queryfuncs_test_domain DEFAULT 'foo1'::queryfuncs_test_domain ON EMPTY);
  json_value 
 ------------