parser: allow trailing commas in json, via opt-in flag.

* parser.c (read_bad_json_s): New symbol variable.
(parser_common_init): Propagate value of *read-bad-json* into
read_bad_json flag in parser structure.
(parser_init): Initialize read_bad_json_s and register the
*read-bad-json* dynamic variable.

* parser.h (struct parser): New member, read_bad_json.
(read_bad_json_s): Declared.

* parser.y (json_val): Support an opt_comma symbol just before
the closing bracket or brace.
(opt_comma): New nonterminal symbol. Recognizes ',' or nothing.
Error is flagged if ',' is recognized, and *read-bad-json*
is nil.

* y.tab.c.shipped: Updated.

* tests/010/json.tl: New tests.

* txr.1: Documented.

1 files changed, 2 insertions, 1 deletions

diff --git a/parser.h b/parser.h
index 3d682daa..69cbf043 100644
--- a/parser.h
+++ b/parser.h
@@ -66,6 +66,7 @@ struct parser {
   int tok_idx;
   int rec_source_loc;
   int read_unknown_structs;
+  int read_bad_json;
 };
 #endif
 
@@ -75,7 +76,7 @@ extern const int have_yydebug;
 extern const wchar_t *spec_file;
 extern val form_to_ln_hash;
 extern val parser_s, unique_s, circref_s;
-extern val rec_source_loc_s, read_unknown_structs_s;
+extern val rec_source_loc_s, read_unknown_structs_s, read_bad_json_s;
 extern val json_s;
 
 extern struct cobj_class *parser_cls;