SQL/JSON: Miscellaneous fixes and improvements

This addresses some post-commit review comments for commits 6185c97,
de36004, and 9425c596a0, with the following changes:

* Fix JSON_TABLE() syntax documentation to use the term
  "path_expression" for JSON path expressions instead of
  "json_path_specification" to be consistent with the other SQL/JSON
  functions.

* Fix a typo in the example code in JSON_TABLE() documentation.

* Rewrite some newly added comments in jsonpath.h.

* In JsonPathQuery(), add missing cast to int before printing an enum
  value.

Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxG_e0QLCgaELrr2ZNz7AxPeGCNKAORe3fHtFCQLsH4J4Q@mail.gmail.com

Author: amitlan

doc/src/sgml/func.sgml

@@ -18942,7 +18942,7 @@ where <replaceable class="parameter">json_table_column</replaceable> is:
         <optional> { ERROR | NULL | EMPTY { ARRAY | OBJECT } | DEFAULT <replaceable>expression</replaceable> } ON ERROR </optional>
   | <replaceable>name</replaceable> <replaceable>type</replaceable> EXISTS <optional> PATH <replaceable>path_expression</replaceable> </optional>
         <optional> { ERROR | TRUE | FALSE | UNKNOWN } ON ERROR </optional>
-  | NESTED <optional> PATH </optional> <replaceable>json_path_specification</replaceable> <optional> AS <replaceable>json_path_name</replaceable> </optional> COLUMNS ( <replaceable>json_table_column</replaceable> <optional>, ...</optional> )
+  | NESTED <optional> PATH </optional> <replaceable>path_expression</replaceable> <optional> AS <replaceable>json_path_name</replaceable> </optional> COLUMNS ( <replaceable>json_table_column</replaceable> <optional>, ...</optional> )
 </synopsis>
 
   <para>
@@ -19083,7 +19083,7 @@ where <replaceable class="parameter">json_table_column</replaceable> is:
 
    <varlistentry>
     <term>
-      <literal>NESTED <optional> PATH </optional></literal> <replaceable>json_path_specification</replaceable> <optional> <literal>AS</literal> <replaceable>json_path_name</replaceable> </optional>
+      <literal>NESTED <optional> PATH </optional></literal> <replaceable>path_expression</replaceable> <optional> <literal>AS</literal> <replaceable>json_path_name</replaceable> </optional>
           <literal>COLUMNS</literal> ( <replaceable>json_table_column</replaceable> <optional>, ...</optional> )
     </term>
     <listitem>
@@ -19315,8 +19315,9 @@ SELECT * FROM JSON_TABLE (
      "books":
       [{"name": "Mystery", "authors": [{"name": "Brown Dan"}]},
        {"name": "Wonder", "authors": [{"name": "Jun Murakami"}, {"name":"Craig Doe"}]}]
-}}'::json, '$.favs[*]'
-COLUMNS (user_id FOR ORDINALITY,
+}}'::json, '$.favorites[*]'
+COLUMNS (
+  user_id FOR ORDINALITY,
   NESTED '$.movies[*]'
     COLUMNS (
     movie_id FOR ORDINALITY,

src/backend/utils/adt/jsonpath_exec.c

@@ -3935,7 +3935,7 @@ JsonPathQuery(Datum jb, JsonPath *jp, JsonWrapper wrapper, bool *empty,
 			 JsonContainerIsScalar(singleton->val.binary.data));
 	else
 	{
-		elog(ERROR, "unrecognized json wrapper %d", wrapper);
+		elog(ERROR, "unrecognized json wrapper %d", (int) wrapper);
 		wrap = false;
 	}
 

src/include/utils/jsonpath.h

@@ -281,12 +281,9 @@ extern JsonPathParseResult *parsejsonpath(const char *str, int len,
 extern bool jspConvertRegexFlags(uint32 xflags, int *result,
 								 struct Node *escontext);
 
-
 /*
- * Evaluation of jsonpath
+ * Struct for details about external variables passed into jsonpath executor
  */
-
-/* External variable passed into jsonpath. */
 typedef struct JsonPathVariable
 {
 	char	   *name;
@@ -297,7 +294,7 @@ typedef struct JsonPathVariable
 } JsonPathVariable;
 
 
-/* SQL/JSON item */
+/* SQL/JSON query functions */
 extern bool JsonPathExists(Datum jb, JsonPath *path, bool *error, List *vars);
 extern Datum JsonPathQuery(Datum jb, JsonPath *jp, JsonWrapper wrapper,
 						   bool *empty, bool *error, List *vars,
@@ -306,6 +303,7 @@ extern JsonbValue *JsonPathValue(Datum jb, JsonPath *jp, bool *empty,
 								 bool *error, List *vars,
 								 const char *column_name);
 
+/* For JSON_TABLE() */
 extern PGDLLIMPORT const TableFuncRoutine JsonbTableRoutine;
 
 #endif