Remove pg_hint_plan.hints_anywhere

This GUC setting was a wart, able to bypass a check to force hints to
happen before and/or after a set of characters.  A weird behavior that
it caused is that it was possible to define a hint within what should be
considered a value in a query.  For example, a query like that would use
a hint:
SELECT * FROM t1 JOIN t2 ON t1.val = t2.val
  WHERE '/*+MergeJoin(t1 t2)*/' <> '';

The reason why this parameter existed to begin with was to be more
liberal with the position of a hint, because pg_hint_plan has always
used a custom parser for query lookups.  An upcoming patch will be able
to solve these problems by introducing a proper query parser in this
extension, based on what upstream uses for psql with yyac.

Note that this GUC was not documented, as well, remaining hidden to the
end-user.

Makefile

@@ -8,7 +8,7 @@ MODULES = pg_hint_plan
 HINTPLANVER = 1.7.0
 
 REGRESS = init base_plan pg_hint_plan ut-init ut-A ut-S ut-J ut-L ut-G ut-R \
-	ut-fdw ut-W ut-T ut-fini hints_anywhere plpgsql oldextversions
+	ut-fdw ut-W ut-T ut-fini plpgsql oldextversions
 REGRESS_OPTS = --encoding=UTF8
 
 EXTENSION = pg_hint_plan

pg_hint_plan.c

@@ -522,7 +522,6 @@ static int	pg_hint_plan_parse_message_level = INFO;
 static int	pg_hint_plan_debug_message_level = LOG;
 /* Default is off, to keep backward compatibility. */
 static bool	pg_hint_plan_enable_hint_table = false;
-static bool	pg_hint_plan_hints_anywhere = false;
 
 static int plpgsql_recurse_level = 0;		/* PLpgSQL recursion level            */
 static int recurse_level = 0;		/* recursion level incl. direct SPI calls */
@@ -773,17 +772,6 @@ _PG_init(void)
 							 assign_enable_hint_table,
 							 NULL);
 
-	DefineCustomBoolVariable("pg_hint_plan.hints_anywhere",
-							 "Read hints from anywhere in a query.",
-							 "This option lets pg_hint_plan ignore syntax so be cautious for false reads.",
-							 &pg_hint_plan_hints_anywhere,
-							 false,
-							 PGC_USERSET,
-							 0,
-							 NULL,
-							 NULL,
-							 NULL);
-
 	EmitWarningsOnPlaceholders("pg_hint_plan");
 
 	/* Install hooks. */
@@ -1973,34 +1961,32 @@ get_hints_from_comment(const char *p)
 	hint_head = strstr(p, HINT_START);
 	if (hint_head == NULL)
 		return NULL;
-	if (!pg_hint_plan_hints_anywhere)
+
+	for (;p < hint_head; p++)
 	{
-		for (;p < hint_head; p++)
-		{
-			/*
-			 * Allow these characters precedes hint comment:
-			 *   - digits
-			 *   - alphabets which are in ASCII range
-			 *   - space, tabs and new-lines
-			 *   - underscores, for identifier
-			 *   - commas, for SELECT clause, EXPLAIN and PREPARE
-			 *   - parentheses, for EXPLAIN and PREPARE
-			 *   - squared brackets, for arrays (like arguments of PREPARE
-			 *     statements).
-			 *
-			 * Note that we don't use isalpha() nor isalnum() in ctype.h here to
-			 * avoid behavior which depends on locale setting.
-			 */
-			if (!(*p >= '0' && *p <= '9') &&
-				!(*p >= 'A' && *p <= 'Z') &&
-				!(*p >= 'a' && *p <= 'z') &&
-				!isspace(*p) &&
-				*p != '_' &&
-				*p != ',' &&
-				*p != '(' && *p != ')' &&
-				*p != '[' && *p != ']')
-				return NULL;
-		}
+		/*
+		 * Allow these characters precedes hint comment:
+		 *   - digits
+		 *   - alphabets which are in ASCII range
+		 *   - space, tabs and new-lines
+		 *   - underscores, for identifier
+		 *   - commas, for SELECT clause, EXPLAIN and PREPARE
+		 *   - parentheses, for EXPLAIN and PREPARE
+		 *   - squared brackets, for arrays (like arguments of PREPARE
+		 *     statements).
+		 *
+		 * Note that we don't use isalpha() nor isalnum() in ctype.h here to
+		 * avoid behavior which depends on locale setting.
+		 */
+		if (!(*p >= '0' && *p <= '9') &&
+			!(*p >= 'A' && *p <= 'Z') &&
+			!(*p >= 'a' && *p <= 'z') &&
+			!isspace(*p) &&
+			*p != '_' &&
+			*p != ',' &&
+			*p != '(' && *p != ')' &&
+			*p != '[' && *p != ']')
+			return NULL;
 	}
 
 	head = (char *)hint_head;