SQL/JSON constructors

This patch introduces the SQL/JSON standard constructors for JSON:

JSON()
JSON_ARRAY()
JSON_ARRAYAGG()
JSON_OBJECT()
JSON_OBJECTAGG()

For the most part these functions provide facilities that mimic
existing json/jsonb functions. However, they also offer some useful
additional functionality. In addition to text input, the JSON() function
accepts bytea input, which it will decode and constuct a json value from.
The other functions provide useful options for handling duplicate keys
and null values.

This series of patches will be followed by a consolidated documentation
patch.

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

4 files changed, 129 insertions, 1 deletions

diff --git a/src/include/nodes/makefuncs.h b/src/include/nodes/makefuncs.h
index ec8b71a6856..e50b933288d 100644
--- a/src/include/nodes/makefuncs.h
+++ b/src/include/nodes/makefuncs.h
@@ -109,6 +109,7 @@ extern VacuumRelation *makeVacuumRelation(RangeVar *relation, Oid oid, List *va_
 extern JsonFormat *makeJsonFormat(JsonFormatType type, JsonEncoding encoding,
 								  int location);
 extern JsonValueExpr *makeJsonValueExpr(Expr *expr, JsonFormat *format);
+extern Node *makeJsonKeyValue(Node *key, Node *value);
 extern JsonEncoding makeJsonEncoding(char *name);
 
 #endif							/* MAKEFUNC_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 59737f10349..05f0b79e82e 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -204,6 +204,7 @@ typedef enum NodeTag
 	T_JsonFormat,
 	T_JsonReturning,
 	T_JsonValueExpr,
+	T_JsonConstructorExpr,
 
 	/*
 	 * TAGS FOR EXPRESSION STATE NODES (execnodes.h)
@@ -494,6 +495,13 @@ typedef enum NodeTag
 	T_VacuumRelation,
 	T_PublicationObjSpec,
 	T_PublicationTable,
+	T_JsonObjectConstructor,
+	T_JsonArrayConstructor,
+	T_JsonArrayQueryConstructor,
+	T_JsonAggConstructor,
+	T_JsonObjectAgg,
+	T_JsonArrayAgg,
+	T_JsonKeyValue,
 	T_JsonOutput,
 
 	/*
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index e06d43d4dfe..3b12a708ec0 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1563,9 +1563,103 @@ typedef struct JsonOutput
 {
 	NodeTag		type;
 	TypeName   *typeName;		/* RETURNING type name, if specified */
-	JsonReturning returning;	/* RETURNING FORMAT clause and type Oids */
+	JsonReturning *returning;	/* RETURNING FORMAT clause and type Oids */
 } JsonOutput;
 
+/*
+ * JsonKeyValue -
+ *		untransformed representation of JSON object key-value pair for
+ *		JSON_OBJECT() and JSON_OBJECTAGG()
+ */
+typedef struct JsonKeyValue
+{
+	NodeTag		type;
+	Expr	   *key;			/* key expression */
+	JsonValueExpr *value;		/* JSON value expression */
+} JsonKeyValue;
+
+/*
+ * JsonObjectConstructor -
+ *		untransformed representation of JSON_OBJECT() constructor
+ */
+typedef struct JsonObjectConstructor
+{
+	NodeTag		type;
+	List	   *exprs;			/* list of JsonKeyValue pairs */
+	JsonOutput *output;			/* RETURNING clause, if specified  */
+	bool		absent_on_null;	/* skip NULL values? */
+	bool		unique;			/* check key uniqueness? */
+	int			location;		/* token location, or -1 if unknown */
+} JsonObjectConstructor;
+
+/*
+ * JsonArrayConstructor -
+ *		untransformed representation of JSON_ARRAY(element,...) constructor
+ */
+typedef struct JsonArrayConstructor
+{
+	NodeTag		type;
+	List	   *exprs;			/* list of JsonValueExpr elements */
+	JsonOutput *output;			/* RETURNING clause, if specified  */
+	bool		absent_on_null;	/* skip NULL elements? */
+	int			location;		/* token location, or -1 if unknown */
+} JsonArrayConstructor;
+
+/*
+ * JsonArrayQueryConstructor -
+ *		untransformed representation of JSON_ARRAY(subquery) constructor
+ */
+typedef struct JsonArrayQueryConstructor
+{
+	NodeTag		type;
+	Node	   *query;			/* subquery */
+	JsonOutput *output;			/* RETURNING clause, if specified  */
+	JsonFormat *format;			/* FORMAT clause for subquery, if specified */
+	bool		absent_on_null;	/* skip NULL elements? */
+	int			location;		/* token location, or -1 if unknown */
+} JsonArrayQueryConstructor;
+
+/*
+ * JsonAggConstructor -
+ *		common fields of untransformed representation of
+ *		JSON_ARRAYAGG() and JSON_OBJECTAGG()
+ */
+typedef struct JsonAggConstructor
+{
+	NodeTag		type;
+	JsonOutput *output;			/* RETURNING clause, if any */
+	Node	   *agg_filter;		/* FILTER clause, if any */
+	List	   *agg_order;		/* ORDER BY clause, if any */
+	struct WindowDef *over;		/* OVER clause, if any */
+	int			location;		/* token location, or -1 if unknown */
+} JsonAggConstructor;
+
+/*
+ * JsonObjectAgg -
+ *		untransformed representation of JSON_OBJECTAGG()
+ */
+typedef struct JsonObjectAgg
+{
+	NodeTag		type;
+	JsonAggConstructor *constructor; /* common fields */
+	JsonKeyValue *arg;			/* object key-value pair */
+	bool		absent_on_null;	/* skip NULL values? */
+	bool		unique;			/* check key uniqueness? */
+} JsonObjectAgg;
+
+/*
+ * JsonArrayAgg -
+ *		untransformed representation of JSON_ARRRAYAGG()
+ */
+typedef struct JsonArrayAgg
+{
+	NodeTag		type;
+	JsonAggConstructor *constructor; /* common fields */
+	JsonValueExpr *arg;			/* array element expression */
+	bool		absent_on_null;	/* skip NULL elements? */
+} JsonArrayAgg;
+
+
 /*****************************************************************************
  *		Raw Grammar Output Statements
  *****************************************************************************/
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 8e3c99bdb52..c48527e998a 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1292,6 +1292,31 @@ typedef struct JsonValueExpr
 	JsonFormat *format;			/* FORMAT clause, if specified */
 } JsonValueExpr;
 
+typedef enum JsonConstructorType
+{
+	JSCTOR_JSON_OBJECT = 1,
+	JSCTOR_JSON_ARRAY = 2,
+	JSCTOR_JSON_OBJECTAGG = 3,
+	JSCTOR_JSON_ARRAYAGG = 4
+} JsonConstructorType;
+
+/*
+ * JsonConstructorExpr -
+ *		wrapper over FuncExpr/Aggref/WindowFunc for SQL/JSON constructors
+ */
+typedef struct JsonConstructorExpr
+{
+	Expr		xpr;
+	JsonConstructorType type;	/* constructor type */
+	List	   *args;
+	Expr	   *func;			/* underlying json[b]_xxx() function call */
+	Expr	   *coercion;		/* coercion to RETURNING type */
+	JsonReturning *returning;	/* RETURNING clause */
+	bool		absent_on_null;	/* ABSENT ON NULL? */
+	bool		unique;			/* WITH UNIQUE KEYS? (JSON_OBJECT[AGG] only) */
+	int			location;
+} JsonConstructorExpr;
+
 /* ----------------
  * NullTest
  *