SQL/JSON: Fix coercion of constructor outputs to types with typmod

Ensure SQL/JSON constructor functions that allow specifying the
target type using the RETURNING clause perform implicit cast to
that type.  This ensures that output values that exceed the specified
length produce an error rather than being  silently truncated. This
behavior conforms to the SQL standard.

Reported-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/202405271326.5a5rprki64aw%40alvherre.pgsql

2 files changed, 29 insertions, 0 deletions

diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index cbf8542d8da..4f91e2117ef 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -1278,3 +1278,20 @@ CREATE OR REPLACE VIEW public.is_json_view AS
     '{}'::text IS JSON OBJECT WITH UNIQUE KEYS AS object
    FROM generate_series(1, 3) i(i)
 DROP VIEW is_json_view;
+-- Test implicit coercion to a fixed-length type specified in RETURNING
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING varchar(2));
+ERROR:  value too long for type character varying(2)
+SELECT JSON_OBJECT('a': JSON_OBJECT('b': 1 RETURNING varchar(2)));
+ERROR:  value too long for type character varying(2)
+SELECT JSON_ARRAY(JSON_ARRAY('{ "a" : 123 }' RETURNING varchar(2)));
+ERROR:  value too long for type character varying(2)
+SELECT JSON_ARRAYAGG(('111' || i)::bytea FORMAT JSON NULL ON NULL RETURNING varchar(2)) FROM generate_series(1,1) i;
+ERROR:  value too long for type character varying(2)
+SELECT JSON_OBJECTAGG(i: ('111' || i)::bytea FORMAT JSON WITH UNIQUE RETURNING varchar(2)) FROM generate_series(1, 1) i;
+ERROR:  value too long for type character varying(2)
+-- Now try domain over fixed-length type
+CREATE DOMAIN sqljson_char2 AS char(2) CHECK (VALUE NOT IN ('12'));
+SELECT JSON_SERIALIZE('123' RETURNING sqljson_char2);
+ERROR:  value too long for type character(2)
+SELECT JSON_SERIALIZE('12' RETURNING sqljson_char2);
+ERROR:  value for domain sqljson_char2 violates check constraint "sqljson_char2_check"
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index e6e20175b00..bb2487e8649 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -463,3 +463,15 @@ SELECT '1' IS JSON AS "any", ('1' || i) IS JSON SCALAR AS "scalar", '[]' IS NOT
 \sv is_json_view
 
 DROP VIEW is_json_view;
+
+-- Test implicit coercion to a fixed-length type specified in RETURNING
+SELECT JSON_SERIALIZE('{ "a" : 1 } ' RETURNING varchar(2));
+SELECT JSON_OBJECT('a': JSON_OBJECT('b': 1 RETURNING varchar(2)));
+SELECT JSON_ARRAY(JSON_ARRAY('{ "a" : 123 }' RETURNING varchar(2)));
+SELECT JSON_ARRAYAGG(('111' || i)::bytea FORMAT JSON NULL ON NULL RETURNING varchar(2)) FROM generate_series(1,1) i;
+SELECT JSON_OBJECTAGG(i: ('111' || i)::bytea FORMAT JSON WITH UNIQUE RETURNING varchar(2)) FROM generate_series(1, 1) i;
+
+-- Now try domain over fixed-length type
+CREATE DOMAIN sqljson_char2 AS char(2) CHECK (VALUE NOT IN ('12'));
+SELECT JSON_SERIALIZE('123' RETURNING sqljson_char2);
+SELECT JSON_SERIALIZE('12' RETURNING sqljson_char2);