Add tests for jsonpath .* on arrays

There was no coverage for the path to unwrap an array before applying
`.*` to it, so add tests that explicitly test `.*` for both objects and
arrays, showing how no results are returned for an array of scalars, but
results are returned when the array contains an object. Also test the
behavior in strict mode with and without the silent parameter, and with
the `@?` operator.

Unrelated but potentially useful to future source readers: document
`GetJsonPathVar` and `CountJsonPathVars`.

Author: theory

src/backend/utils/adt/jsonpath_exec.c

@@ -2978,7 +2978,8 @@ getJsonPathItem(JsonPathExecContext *cxt, JsonPathItem *item,
 }
 
 /*
- * Returns the computed value of a JSON path variable with given name.
+ * Definition of JsonPathGetVarCallback for when JsonPathExecContext.vars
+ * is specified as a List value.
  */
 static JsonbValue *
 GetJsonPathVar(void *cxt, char *varName, int varNameLen,
@@ -3025,6 +3026,10 @@ GetJsonPathVar(void *cxt, char *varName, int varNameLen,
 	return result;
 }
 
+/*
+ * Definition of JsonPathCountVarsCallback for when JsonPathExecContext.vars
+ * is specified as a List value.
+ */
 static int
 CountJsonPathVars(void *cxt)
 {

src/test/regress/expected/jsonb_jsonpath.out

@@ -4394,3 +4394,53 @@ ORDER BY s1.num, s2.num;
  {"s": "B"}    | {"s": "B"}    | false | true  | true  | true  | false
 (144 rows)
 
+-- Test any key on arrays with and without unwrapping.
+select jsonb_path_query('{"a": [1,2,3], "b": [3,4,5]}', '$.*');
+ jsonb_path_query 
+------------------
+ [1, 2, 3]
+ [3, 4, 5]
+(2 rows)
+
+select jsonb_path_query('[1,2,3]', '$.*');
+ jsonb_path_query 
+------------------
+(0 rows)
+
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'lax $.*');
+ jsonb_path_query 
+------------------
+ [3, 4, 5]
+(1 row)
+
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'strict $.*');
+ERROR:  jsonpath wildcard member accessor can only be applied to an object
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'strict $.*', NULL, true);
+ jsonb_path_query 
+------------------
+(0 rows)
+
+select jsonb '{"a": [1,2,3], "b": [3,4,5]}' @? '$.*';
+ ?column? 
+----------
+ t
+(1 row)
+
+select jsonb '[1,2,3]' @? '$.*';
+ ?column? 
+----------
+ f
+(1 row)
+
+select jsonb '[1,2,3,{"b": [3,4,5]}]' @? 'lax $.*';
+ ?column? 
+----------
+ t
+(1 row)
+
+select jsonb '[1,2,3,{"b": [3,4,5]}]' @? 'strict $.*';
+ ?column? 
+----------
+ 
+(1 row)
+

src/test/regress/sql/jsonb_jsonpath.sql

@@ -1116,3 +1116,14 @@ SELECT
 	jsonb_path_query_first(s1.j, '$.s > $s', vars => s2.j) gt
 FROM str s1, str s2
 ORDER BY s1.num, s2.num;
+
+-- Test any key on arrays with and without unwrapping.
+select jsonb_path_query('{"a": [1,2,3], "b": [3,4,5]}', '$.*');
+select jsonb_path_query('[1,2,3]', '$.*');
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'lax $.*');
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'strict $.*');
+select jsonb_path_query('[1,2,3,{"b": [3,4,5]}]', 'strict $.*', NULL, true);
+select jsonb '{"a": [1,2,3], "b": [3,4,5]}' @? '$.*';
+select jsonb '[1,2,3]' @? '$.*';
+select jsonb '[1,2,3,{"b": [3,4,5]}]' @? 'lax $.*';
+select jsonb '[1,2,3,{"b": [3,4,5]}]' @? 'strict $.*';