SQL/JSON: Fix some oversights in commit b6e1157e7

The decision in b6e1157e7 to ignore raw_expr when evaluating a
JsonValueExpr was incorrect.  While its value is not ultimately
used (since formatted_expr's value is), failing to initialize it
can lead to problems, for instance,  when the expression tree in
raw_expr contains Aggref nodes, which must be initialized to
ensure the parent Agg node works correctly.

Also, optimize eval_const_expressions_mutator()'s handling of
JsonValueExpr a bit.  Currently, when formatted_expr cannot be folded
into a constant, we end up processing it twice -- once directly in
eval_const_expressions_mutator() and again recursively via
ece_generic_processing().  This recursive processing is required to
handle raw_expr. To avoid the redundant processing of formatted_expr,
we now  process raw_expr directly in eval_const_expressions_mutator().

Finally, update the comment of JsonValueExpr to describe the roles of
raw_expr and formatted_expr more clearly.

Bug: #18657
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Diagnosed-by: Fabio R. Sluzala <fabio3rs@gmail.com>
Diagnosed-by: Tender Wang <tndrwang@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/18657-1b90ccce2b16bdb8@postgresql.org
Backpatch-through: 16

2 files changed, 63 insertions, 0 deletions

diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index 9adfbe15f65..70721c9a5ad 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -1300,3 +1300,52 @@ 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"
+-- Bug #18657: JsonValueExpr.raw_expr was not initialized in ExecInitExprRec()
+-- causing the Aggrefs contained in it to also not be initialized, which led
+-- to a crash in ExecBuildAggTrans() as mentioned in the bug report:
+-- https://postgr.es/m/18657-1b90ccce2b16bdb8@postgresql.org
+CREATE FUNCTION volatile_one() RETURNS int AS $$ BEGIN RETURN 1; END; $$ LANGUAGE plpgsql VOLATILE;
+CREATE FUNCTION stable_one() RETURNS int AS $$ BEGIN RETURN 1; END; $$ LANGUAGE plpgsql STABLE;
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': volatile_one() RETURNING text) FORMAT JSON);
+                                                 QUERY PLAN                                                  
+-------------------------------------------------------------------------------------------------------------
+ Aggregate
+   Output: JSON_OBJECT('a' : JSON_OBJECTAGG('b' : volatile_one() RETURNING text) FORMAT JSON RETURNING json)
+   ->  Result
+(3 rows)
+
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': volatile_one() RETURNING text) FORMAT JSON);
+     json_object     
+---------------------
+ {"a" : { "b" : 1 }}
+(1 row)
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': stable_one() RETURNING text) FORMAT JSON);
+                                                QUERY PLAN                                                 
+-----------------------------------------------------------------------------------------------------------
+ Aggregate
+   Output: JSON_OBJECT('a' : JSON_OBJECTAGG('b' : stable_one() RETURNING text) FORMAT JSON RETURNING json)
+   ->  Result
+(3 rows)
+
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': stable_one() RETURNING text) FORMAT JSON);
+     json_object     
+---------------------
+ {"a" : { "b" : 1 }}
+(1 row)
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': 1 RETURNING text) FORMAT JSON);
+                                           QUERY PLAN                                           
+------------------------------------------------------------------------------------------------
+ Aggregate
+   Output: JSON_OBJECT('a' : JSON_OBJECTAGG('b' : 1 RETURNING text) FORMAT JSON RETURNING json)
+   ->  Result
+(3 rows)
+
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': 1 RETURNING text) FORMAT JSON);
+     json_object     
+---------------------
+ {"a" : { "b" : 1 }}
+(1 row)
+
+DROP FUNCTION volatile_one, stable_one;
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index 42dbec26d6f..9b5d82602d0 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -480,3 +480,17 @@ SELECT JSON_OBJECTAGG(i: ('111' || i)::bytea FORMAT JSON WITH UNIQUE RETURNING v
 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);
+
+-- Bug #18657: JsonValueExpr.raw_expr was not initialized in ExecInitExprRec()
+-- causing the Aggrefs contained in it to also not be initialized, which led
+-- to a crash in ExecBuildAggTrans() as mentioned in the bug report:
+-- https://postgr.es/m/18657-1b90ccce2b16bdb8@postgresql.org
+CREATE FUNCTION volatile_one() RETURNS int AS $$ BEGIN RETURN 1; END; $$ LANGUAGE plpgsql VOLATILE;
+CREATE FUNCTION stable_one() RETURNS int AS $$ BEGIN RETURN 1; END; $$ LANGUAGE plpgsql STABLE;
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': volatile_one() RETURNING text) FORMAT JSON);
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': volatile_one() RETURNING text) FORMAT JSON);
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': stable_one() RETURNING text) FORMAT JSON);
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': stable_one() RETURNING text) FORMAT JSON);
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': 1 RETURNING text) FORMAT JSON);
+SELECT JSON_OBJECT('a': JSON_OBJECTAGG('b': 1 RETURNING text) FORMAT JSON);
+DROP FUNCTION volatile_one, stable_one;