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, 73 insertions, 0 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 92593526725..1774c56ae31 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1008,6 +1008,79 @@ typedef struct DomainConstraintState
 	ExprState  *check_exprstate;	/* check_expr's eval state, or NULL */
 } DomainConstraintState;
 
+/*
+ * State for JsonExpr evaluation, too big to inline.
+ *
+ * This contains the information going into and coming out of the
+ * EEOP_JSONEXPR_PATH eval step.
+ */
+typedef struct JsonExprState
+{
+	/* original expression node */
+	JsonExpr   *jsexpr;
+
+	/* value/isnull for formatted_expr */
+	NullableDatum formatted_expr;
+
+	/* value/isnull for pathspec */
+	NullableDatum pathspec;
+
+	/* JsonPathVariable entries for passing_values */
+	List	   *args;
+
+	/*
+	 * Output variables that drive the EEOP_JUMP_IF_NOT_TRUE steps that are
+	 * added for ON ERROR and ON EMPTY expressions, if any.
+	 *
+	 * Reset for each evaluation of EEOP_JSONEXPR_PATH.
+	 */
+
+	/* Set to true if jsonpath evaluation cause an error.  */
+	NullableDatum error;
+
+	/* Set to true if the jsonpath evaluation returned 0 items. */
+	NullableDatum empty;
+
+	/*
+	 * Addresses of steps that implement the non-ERROR variant of ON EMPTY and
+	 * ON ERROR behaviors, respectively.
+	 */
+	int			jump_empty;
+	int			jump_error;
+
+	/*
+	 * Address of the step to coerce the result value of jsonpath evaluation
+	 * to the RETURNING type using JsonExpr.coercion_expr.  -1 if no coercion
+	 * is necessary or if either JsonExpr.use_io_coercion or
+	 * JsonExpr.use_json_coercion is true.
+	 */
+	int			jump_eval_coercion;
+
+	/*
+	 * Address to jump to when skipping all the steps after performing
+	 * ExecEvalJsonExprPath() so as to return whatever the JsonPath* function
+	 * returned as is, that is, in the cases where there's no error and no
+	 * coercion is necessary.
+	 */
+	int			jump_end;
+
+	/*
+	 * RETURNING type input function invocation info when
+	 * JsonExpr.use_io_coercion is true.
+	 */
+	FmgrInfo   *input_finfo;
+	FunctionCallInfo input_fcinfo;
+
+	/*
+	 * For error-safe evaluation of coercions.  When the ON ERROR behavior is
+	 * not ERROR, a pointer to this is passed to ExecInitExprRec() when
+	 * initializing the coercion expressions or to ExecInitJsonCoercion().
+	 *
+	 * Reset for each evaluation of EEOP_JSONEXPR_PATH.
+	 */
+	ErrorSaveContext escontext;
+} JsonExprState;
+
 
 /* ----------------------------------------------------------------
  *				 Executor State Trees