Add SQL/JSON query functions

This introduces the following SQL/JSON functions for querying JSON
data using jsonpath expressions:

JSON_EXISTS(), which can be used to apply a jsonpath expression to a
JSON value to check if it yields any values.

JSON_QUERY(), which can be used to to apply a jsonpath expression to
a JSON value to get a JSON object, an array, or a string.  There are
various options to control whether multi-value result uses array
wrappers and whether the singleton scalar strings are quoted or not.

JSON_VALUE(), which can be used to apply a jsonpath expression to a
JSON value to return a single scalar value, producing an error if it
multiple values are matched.

Both JSON_VALUE() and JSON_QUERY() functions have options for
handling EMPTY and ERROR conditions, which can be used to specify
the behavior when no values are matched and when an error occurs
during jsonpath evaluation, respectively.

Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Andrew Dunstan <andrew@dunslane.net>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Peter Eisentraut <peter@eisentraut.org>
Author: Jian He <jian.universality@gmail.com>

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, Álvaro Herrera, Jian He, Anton A. Melnikov,
Nikita Malakhov, Peter Eisentraut, Tomas Vondra

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
Discussion: https://postgr.es/m/CA+HiwqHROpf9e644D8BRqYvaAPmgBZVup-xKMDPk-nd4EpgzHw@mail.gmail.com
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com

1 files changed, 122 insertions, 0 deletions

diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index e57d69f72e2..376f67e6a5f 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1691,6 +1691,128 @@ typedef struct JsonIsPredicate
 	ParseLoc	location;		/* token location, or -1 if unknown */
 } JsonIsPredicate;
 
+/* Nodes used in SQL/JSON query functions */
+
+/*
+ * JsonWrapper -
+ *		representation of WRAPPER clause for JSON_QUERY()
+ */
+typedef enum JsonWrapper
+{
+	JSW_UNSPEC,
+	JSW_NONE,
+	JSW_CONDITIONAL,
+	JSW_UNCONDITIONAL,
+} JsonWrapper;
+
+/*
+ * JsonBehaviorType -
+ *		enumeration of behavior types used in SQL/JSON ON ERROR/EMPTY clauses
+ *
+ * 		If enum members are reordered, get_json_behavior() from ruleutils.c
+ * 		must be updated accordingly.
+ */
+typedef enum JsonBehaviorType
+{
+	JSON_BEHAVIOR_NULL = 0,
+	JSON_BEHAVIOR_ERROR,
+	JSON_BEHAVIOR_EMPTY,
+	JSON_BEHAVIOR_TRUE,
+	JSON_BEHAVIOR_FALSE,
+	JSON_BEHAVIOR_UNKNOWN,
+	JSON_BEHAVIOR_EMPTY_ARRAY,
+	JSON_BEHAVIOR_EMPTY_OBJECT,
+	JSON_BEHAVIOR_DEFAULT,
+} JsonBehaviorType;
+
+/*
+ * JsonBehavior
+ *		Specifications for ON ERROR / ON EMPTY behaviors of SQL/JSON
+ *		query functions specified by a JsonExpr
+ *
+ * 'expr' is the expression to emit when a given behavior (EMPTY or ERROR)
+ * occurs on evaluating the SQL/JSON query function.  'coerce' is set to true
+ * if 'expr' isn't already of the expected target type given by
+ * JsonExpr.returning.
+ */
+typedef struct JsonBehavior
+{
+	NodeTag		type;
+
+	JsonBehaviorType btype;
+	Node	   *expr;
+	bool		coerce;
+	int			location;		/* token location, or -1 if unknown */
+} JsonBehavior;
+
+/*
+ * JsonExprOp -
+ *		enumeration of SQL/JSON query function types
+ */
+typedef enum JsonExprOp
+{
+	JSON_EXISTS_OP,				/* JSON_EXISTS() */
+	JSON_QUERY_OP,				/* JSON_QUERY() */
+	JSON_VALUE_OP,				/* JSON_VALUE() */
+} JsonExprOp;
+
+/*
+ * JsonExpr -
+ *		Transformed representation of JSON_VALUE(), JSON_QUERY(), and
+ *		JSON_EXISTS()
+ */
+typedef struct JsonExpr
+{
+	Expr		xpr;
+
+	JsonExprOp	op;
+
+	/* jsonb-valued expression to query */
+	Node	   *formatted_expr;
+
+	/* Format of the above expression needed by ruleutils.c */
+	JsonFormat *format;
+
+	/* jsopath-valued expression containing the query pattern */
+	Node	   *path_spec;
+
+	/* Expected type/format of the output. */
+	JsonReturning *returning;
+
+	/* Information about the PASSING argument expressions */
+	List	   *passing_names;
+	List	   *passing_values;
+
+	/* User-specified or default ON EMPTY and ON ERROR behaviors */
+	JsonBehavior *on_empty;
+	JsonBehavior *on_error;
+
+	/*
+	 * Information about converting the result of jsonpath functions
+	 * JsonPathQuery() and JsonPathValue() to the RETURNING type.
+	 *
+	 * coercion_expr is a cast expression if the parser can find it for the
+	 * source and the target type.  If not, either use_io_coercion or
+	 * use_json_coercion is set to determine the coercion method to use at
+	 * runtime; see coerceJsonExprOutput() and ExecInitJsonExpr().
+	 */
+	Node	   *coercion_expr;
+	bool		use_io_coercion;
+	bool		use_json_coercion;
+
+	/* WRAPPER specification for JSON_QUERY */
+	JsonWrapper wrapper;
+
+	/* KEEP or OMIT QUOTES for singleton scalars returned by JSON_QUERY() */
+	bool		omit_quotes;
+
+	/* JsonExpr's collation, if coercion_expr is NULL. */
+	Oid			collation;
+
+	/* Original JsonFuncExpr's location */
+	int			location;
+} JsonExpr;
+
 /* ----------------
  * NullTest
  *