From 95097ef835b63baf8af02208fa5ff2d8f0c7605f Mon Sep 17 00:00:00 2001
From: Andrew Dunstan <andrew@dunslane.net>
Date: Sat, 5 Mar 2022 08:07:15 -0500
Subject: [PATCH v2 06/11] RETURNING clause for JSON() and JSON_SCALAR()

This patch is extracted from a larger patch that allowed setting the
default returned value from these functions to json or jsonb. That had
problems, but this piece of it is fine. For these functions only json or
jsonb can be specified in the RETURNING clause.

Extracted from an original patch from Nikita Glukhov

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
---
 src/backend/nodes/nodeFuncs.c         | 20 +++++++++-
 src/backend/parser/gram.y             |  7 +++-
 src/backend/parser/parse_expr.c       | 46 ++++++++++++++++-----
 src/backend/utils/adt/ruleutils.c     |  5 ++-
 src/include/nodes/parsenodes.h        |  8 +---
 src/test/regress/expected/sqljson.out | 57 +++++++++++++++++++++++++++
 src/test/regress/sql/sqljson.sql      | 10 +++++
 7 files changed, 131 insertions(+), 22 deletions(-)

diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index 0d393dfe69..ced888ea5a 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -4332,9 +4332,25 @@ raw_expression_tree_walker_impl(Node *node,
 			}
 			break;
 		case T_JsonParseExpr:
-			return WALK(((JsonParseExpr *) node)->expr);
+			{
+				JsonParseExpr *jpe = (JsonParseExpr *) node;
+
+				if (WALK(jpe->expr))
+					return true;
+				if (WALK(jpe->output))
+					return true;
+			}
+			break;
 		case T_JsonScalarExpr:
-			return WALK(((JsonScalarExpr *) node)->expr);
+			{
+				JsonScalarExpr *jse = (JsonScalarExpr *) node;
+
+				if (WALK(jse->expr))
+					return true;
+				if (WALK(jse->output))
+					return true;
+			}
+			break;
 		case T_JsonSerializeExpr:
 			{
 				JsonSerializeExpr *jse = (JsonSerializeExpr *) node;
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index ef5d45dfad..e78991b424 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -16439,23 +16439,26 @@ json_func_expr:
 		;
 
 json_parse_expr:
-			JSON '(' json_value_expr json_key_uniqueness_constraint_opt ')'
+			JSON '(' json_value_expr json_key_uniqueness_constraint_opt
+					 json_returning_clause_opt ')'
 				{
 					JsonParseExpr *n = makeNode(JsonParseExpr);
 
 					n->expr = (JsonValueExpr *) $3;
 					n->unique_keys = $4;
+					n->output = (JsonOutput *) $5;
 					n->location = @1;
 					$$ = (Node *) n;
 				}
 		;
 
 json_scalar_expr:
-			JSON_SCALAR '(' a_expr ')'
+			JSON_SCALAR '(' a_expr json_returning_clause_opt ')'
 				{
 					JsonScalarExpr *n = makeNode(JsonScalarExpr);
 
 					n->expr = (Expr *) $3;
+					n->output = (JsonOutput *) $4;
 					n->location = @1;
 					$$ = (Node *) n;
 				}
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 8b6a7bc29d..a572fb4f73 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -4390,19 +4390,48 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
 	return (Node *) jsexpr;
 }
 
+static JsonReturning *
+transformJsonConstructorRet(ParseState *pstate, JsonOutput *output, const char *fname)
+{
+	JsonReturning *returning;
+
+	if (output)
+	{
+		returning = transformJsonOutput(pstate, output, false);
+
+		Assert(OidIsValid(returning->typid));
+
+		if (returning->typid != JSONOID && returning->typid != JSONBOID)
+			ereport(ERROR,
+					(errcode(ERRCODE_DATATYPE_MISMATCH),
+					 errmsg("cannot use RETURNING type %s in %s",
+							format_type_be(returning->typid), fname),
+					 parser_errposition(pstate, output->typeName->location)));
+	}
+	else
+	{
+		Oid			targettype = JSONOID;
+		JsonFormatType format = JS_FORMAT_JSON;
+
+		returning = makeNode(JsonReturning);
+		returning->format = makeJsonFormat(format, JS_ENC_DEFAULT, -1);
+		returning->typid = targettype;
+		returning->typmod = -1;
+	}
+
+	return returning;
+}
+
 /*
  * Transform a JSON() expression.
  */
 static Node *
 transformJsonParseExpr(ParseState *pstate, JsonParseExpr *jsexpr)
 {
-	JsonReturning *returning = makeNode(JsonReturning);
+	JsonReturning *returning = transformJsonConstructorRet(pstate, jsexpr->output,
+														   "JSON()");
 	Node	   *arg;
 
-	returning->format = makeJsonFormat(JS_FORMAT_JSON, JS_ENC_DEFAULT, -1);
-	returning->typid = JSONOID;
-	returning->typmod = -1;
-
 	if (jsexpr->unique_keys)
 	{
 		/*
@@ -4442,12 +4471,9 @@ transformJsonParseExpr(ParseState *pstate, JsonParseExpr *jsexpr)
 static Node *
 transformJsonScalarExpr(ParseState *pstate, JsonScalarExpr *jsexpr)
 {
-	JsonReturning *returning = makeNode(JsonReturning);
 	Node	   *arg = transformExprRecurse(pstate, (Node *) jsexpr->expr);
-
-	returning->format = makeJsonFormat(JS_FORMAT_JSON, JS_ENC_DEFAULT, -1);
-	returning->typid = JSONOID;
-	returning->typmod = -1;
+	JsonReturning *returning = transformJsonConstructorRet(pstate, jsexpr->output,
+														   "JSON_SCALAR()");
 
 	if (exprType(arg) == UNKNOWNOID)
 		arg = coerce_to_specific_type(pstate, arg, TEXTOID, "JSON_SCALAR");
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 6b89e6ec64..893c97a7dd 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -10062,8 +10062,9 @@ get_json_constructor_options(JsonConstructorExpr *ctor, StringInfo buf)
 	if (ctor->unique)
 		appendStringInfoString(buf, " WITH UNIQUE KEYS");
 
-	if (ctor->type != JSCTOR_JSON_PARSE &&
-		ctor->type != JSCTOR_JSON_SCALAR)
+	if (!((ctor->type == JSCTOR_JSON_PARSE ||
+		   ctor->type == JSCTOR_JSON_SCALAR) &&
+		  ctor->returning->typid == JSONOID))
 		get_json_returning(ctor->returning, buf, true);
 }
 
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 8d730a0375..f30e5df408 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1638,12 +1638,6 @@ typedef enum JsonQuotes
 	JS_QUOTES_OMIT				/* OMIT QUOTES */
 } JsonQuotes;
 
-/*
- * JsonPathSpec -
- *		representation of JSON path constant
- */
-typedef char *JsonPathSpec;
-
 /*
  * JsonOutput -
  *		representation of JSON output clause (RETURNING type [FORMAT format])
@@ -1717,6 +1711,7 @@ typedef struct JsonParseExpr
 {
 	NodeTag		type;
 	JsonValueExpr *expr;		/* string expression */
+	JsonOutput *output;			/* RETURNING clause, if specified */
 	bool		unique_keys;	/* WITH UNIQUE KEYS? */
 	int			location;		/* token location, or -1 if unknown */
 } JsonParseExpr;
@@ -1729,6 +1724,7 @@ typedef struct JsonScalarExpr
 {
 	NodeTag		type;
 	Expr	   *expr;			/* scalar expression */
+	JsonOutput *output;			/* RETURNING clause, if specified */
 	int			location;		/* token location, or -1 if unknown */
 } JsonScalarExpr;
 
diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index cafacf9dbc..748dfdb04d 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -113,6 +113,49 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' WITHOUT UNIQUE KEYS);
    Output: JSON('123'::json)
 (2 rows)
 
+SELECT JSON('123' RETURNING text);
+ERROR:  cannot use RETURNING type text in JSON()
+LINE 1: SELECT JSON('123' RETURNING text);
+                                    ^
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123');
+         QUERY PLAN          
+-----------------------------
+ Result
+   Output: JSON('123'::json)
+(2 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' RETURNING json);
+         QUERY PLAN          
+-----------------------------
+ Result
+   Output: JSON('123'::json)
+(2 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' RETURNING jsonb);
+                  QUERY PLAN                  
+----------------------------------------------
+ Result
+   Output: JSON('123'::jsonb RETURNING jsonb)
+(2 rows)
+
+SELECT pg_typeof(JSON('123'));
+ pg_typeof 
+-----------
+ json
+(1 row)
+
+SELECT pg_typeof(JSON('123' RETURNING json));
+ pg_typeof 
+-----------
+ json
+(1 row)
+
+SELECT pg_typeof(JSON('123' RETURNING jsonb));
+ pg_typeof 
+-----------
+ jsonb
+(1 row)
+
 -- JSON_SCALAR()
 SELECT JSON_SCALAR();
 ERROR:  syntax error at or near ")"
@@ -204,6 +247,20 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR('123');
    Output: JSON_SCALAR('123'::text)
 (2 rows)
 
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR(123 RETURNING json);
+         QUERY PLAN         
+----------------------------
+ Result
+   Output: JSON_SCALAR(123)
+(2 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR(123 RETURNING jsonb);
+                 QUERY PLAN                 
+--------------------------------------------
+ Result
+   Output: JSON_SCALAR(123 RETURNING jsonb)
+(2 rows)
+
 -- JSON_SERIALIZE()
 SELECT JSON_SERIALIZE();
 ERROR:  syntax error at or near ")"
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index c8d3b80c9e..c2742b40f1 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -23,6 +23,14 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123'::bytea FORMAT JSON ENCODING UTF8)
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' WITH UNIQUE KEYS);
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' WITHOUT UNIQUE KEYS);
 
+SELECT JSON('123' RETURNING text);
+
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123');
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' RETURNING json);
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON('123' RETURNING jsonb);
+SELECT pg_typeof(JSON('123'));
+SELECT pg_typeof(JSON('123' RETURNING json));
+SELECT pg_typeof(JSON('123' RETURNING jsonb));
 
 -- JSON_SCALAR()
 SELECT JSON_SCALAR();
@@ -41,6 +49,8 @@ SELECT JSON_SCALAR('{}'::jsonb);
 
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR(123);
 EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR('123');
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR(123 RETURNING json);
+EXPLAIN (VERBOSE, COSTS OFF) SELECT JSON_SCALAR(123 RETURNING jsonb);
 
 -- JSON_SERIALIZE()
 SELECT JSON_SERIALIZE();
-- 
2.35.3

