Common SQL/JSON clauses

This introduces some of the building blocks used by the SQL/JSON
constructor and query functions. Specifically, it provides node
executor and grammar support for the FORMAT JSON [ENCODING foo]
clause, and values decorated with it, and for the RETURNING clause.

The following SQL/JSON patches will leverage these.

Nikita Glukhov (who probably deserves an award for perseverance).

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, 81 insertions, 0 deletions

diff --git a/src/include/nodes/makefuncs.h b/src/include/nodes/makefuncs.h
index 50de4c62af7..ec8b71a6856 100644
--- a/src/include/nodes/makefuncs.h
+++ b/src/include/nodes/makefuncs.h
@@ -106,4 +106,9 @@ extern GroupingSet *makeGroupingSet(GroupingSetKind kind, List *content, int loc
 
 extern VacuumRelation *makeVacuumRelation(RangeVar *relation, Oid oid, List *va_cols);
 
+extern JsonFormat *makeJsonFormat(JsonFormatType type, JsonEncoding encoding,
+								  int location);
+extern JsonValueExpr *makeJsonValueExpr(Expr *expr, JsonFormat *format);
+extern JsonEncoding makeJsonEncoding(char *name);
+
 #endif							/* MAKEFUNC_H */
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 5d075f0c346..59737f10349 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -201,6 +201,9 @@ typedef enum NodeTag
 	T_FromExpr,
 	T_OnConflictExpr,
 	T_IntoClause,
+	T_JsonFormat,
+	T_JsonReturning,
+	T_JsonValueExpr,
 
 	/*
 	 * TAGS FOR EXPRESSION STATE NODES (execnodes.h)
@@ -491,6 +494,7 @@ typedef enum NodeTag
 	T_VacuumRelation,
 	T_PublicationObjSpec,
 	T_PublicationTable,
+	T_JsonOutput,
 
 	/*
 	 * TAGS FOR REPLICATION GRAMMAR PARSE NODES (replnodes.h)
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 5a458c42e5e..e06d43d4dfe 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1553,6 +1553,19 @@ typedef struct TriggerTransition
 	bool		isTable;
 } TriggerTransition;
 
+/* Nodes for SQL/JSON support */
+
+/*
+ * JsonOutput -
+ *		representation of JSON output clause (RETURNING type [FORMAT format])
+ */
+typedef struct JsonOutput
+{
+	NodeTag		type;
+	TypeName   *typeName;		/* RETURNING type name, if specified */
+	JsonReturning returning;	/* RETURNING FORMAT clause and type Oids */
+} JsonOutput;
+
 /*****************************************************************************
  *		Raw Grammar Output Statements
  *****************************************************************************/
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 439e4b4a9db..8e3c99bdb52 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1233,6 +1233,65 @@ typedef struct XmlExpr
 	int			location;		/* token location, or -1 if unknown */
 } XmlExpr;
 
+/*
+ * JsonEncoding -
+ *		representation of JSON ENCODING clause
+ */
+typedef enum JsonEncoding
+{
+	JS_ENC_DEFAULT,				/* unspecified */
+	JS_ENC_UTF8,
+	JS_ENC_UTF16,
+	JS_ENC_UTF32,
+} JsonEncoding;
+
+/*
+ * JsonFormatType -
+ *		enumeration of JSON formats used in JSON FORMAT clause
+ */
+typedef enum JsonFormatType
+{
+	JS_FORMAT_DEFAULT,			/* unspecified */
+	JS_FORMAT_JSON,				/* FORMAT JSON [ENCODING ...] */
+	JS_FORMAT_JSONB				/* implicit internal format for RETURNING jsonb */
+} JsonFormatType;
+
+/*
+ * JsonFormat -
+ *		representation of JSON FORMAT clause
+ */
+typedef struct JsonFormat
+{
+	NodeTag		type;
+	JsonFormatType format_type;	/* format type */
+	JsonEncoding encoding;		/* JSON encoding */
+	int			location;		/* token location, or -1 if unknown */
+} JsonFormat;
+
+/*
+ * JsonReturning -
+ *		transformed representation of JSON RETURNING clause
+ */
+typedef struct JsonReturning
+{
+	NodeTag		type;
+	JsonFormat *format;			/* output JSON format */
+	Oid			typid;			/* target type Oid */
+	int32		typmod;			/* target type modifier */
+} JsonReturning;
+
+/*
+ * JsonValueExpr -
+ *		representation of JSON value expression (expr [FORMAT json_format])
+ */
+typedef struct JsonValueExpr
+{
+	NodeTag		type;
+	Expr	   *raw_expr;		/* raw expression */
+	Expr	   *formatted_expr;	/* formatted expression or NULL */
+	JsonFormat *format;			/* FORMAT clause, if specified */
+} JsonValueExpr;
+
 /* ----------------
  * NullTest
  *