Fix parse error with comment on last line.

If a comment is not followed by a newline character, then
we got a false parse error. This is because the comment
state is left on the parse stack when we finished parsing, and
since the parse stack was not emtpy, we assumed an error.

This commit adds the parser/eof function, which lets the parser know
that an eof was reached. Before, we simply added a fake newline
character in some cases, and in the case of reading a file, we did
nothing, hence the bug.

src/core/parse.c

@@ -531,20 +531,34 @@ static int root(JanetParser *p, JanetParseState *state, uint8_t c) {
     }
 }
 
-int janet_parser_consume(JanetParser *parser, uint8_t c) {
+static void janet_parser_checkdead(JanetParser *parser) {
+    if (parser->flag) janet_panic("parser is dead, cannot consume");
+    if (parser->error) janet_panic("parser has unchecked error, cannot consume");
+}
+
+/* Public API */
+
+void janet_parser_consume(JanetParser *parser, uint8_t c) {
     int consumed = 0;
-    if (parser->error) return 0;
+    janet_parser_checkdead(parser);
     parser->offset++;
     while (!consumed && !parser->error) {
         JanetParseState *state = parser->states + parser->statecount - 1;
         consumed = state->consumer(parser, state, c);
     }
     parser->lookback = c;
-    return 1;
+}
+
+void janet_parser_eof(JanetParser *parser) {
+    janet_parser_checkdead(parser);
+    janet_parser_consume(parser, '\n');
+    parser->offset--;
+    parser->flag = 1;
 }
 
 enum JanetParserStatus janet_parser_status(JanetParser *parser) {
     if (parser->error) return JANET_PARSE_ERROR;
+    if (parser->flag) return JANET_PARSE_DEAD;
     if (parser->statecount > 1) return JANET_PARSE_PENDING;
     return JANET_PARSE_ROOT;
 }
@@ -594,6 +608,7 @@ void janet_parser_init(JanetParser *parser) {
     parser->lookback = -1;
     parser->offset = 0;
     parser->pending = 0;
+    parser->flag = 0;
 
     pushstate(parser, root, PFLAG_CONTAINER);
 }
@@ -669,6 +684,13 @@ static Janet cfun_parse_consume(int32_t argc, Janet *argv) {
     return janet_wrap_integer(i);
 }
 
+static Janet cfun_parse_eof(int32_t argc, Janet *argv) {
+    janet_fixarity(argc, 1);
+    JanetParser *p = janet_getabstract(argv, 0, &janet_parse_parsertype);
+    janet_parser_eof(p);
+    return argv[0];
+}
+
 static Janet cfun_parse_insert(int32_t argc, Janet *argv) {
     janet_fixarity(argc, 2);
     JanetParser *p = janet_getabstract(argv, 0, &janet_parse_parsertype);
@@ -730,6 +752,9 @@ static Janet cfun_parse_status(int32_t argc, Janet *argv) {
         case JANET_PARSE_ROOT:
             stat = "root";
             break;
+        case JANET_PARSE_DEAD:
+            stat = "dead";
+            break;
     }
     return janet_ckeywordv(stat);
 }
@@ -801,6 +826,7 @@ static const JanetMethod parser_methods[] = {
     {"state", cfun_parse_state},
     {"status", cfun_parse_status},
     {"where", cfun_parse_where},
+    {"eof", cfun_parse_eof},
     {NULL, NULL}
 };
 
@@ -880,6 +906,11 @@ static const JanetReg parse_cfuns[] = {
              "in the byte stream as a tuple (line, column). Lines and columns are counted from "
              "1, (the first byte is line 1, column 1) and a newline is considered ASCII 0x0A.")
     },
+    {
+        "parser/eof", cfun_parse_eof,
+        JDOC("(parser/insert parser)\n\n"
+             "Indicate that the end of file was reached to the parser. This puts the parser in the :dead state.")
+    },
     {
         "parser/insert", cfun_parse_insert,
         JDOC("(parser/insert parser value)\n\n"