parser: fix problems at EOF involving #; syntax.

This patch addresses a problem whereby if a TXR Lisp file ends
with an erased object notation such as #;(a b c), there is a
syntax error.

The strategy is to simplify the grammar so that a single
yyparse primed with SECRET_ESCAPE_E or SECRET_ESCAPE_I will
read either an object, or just one instance of the #;
notation. If #;OBJ is read, then the parse tree is returned as
the nao value. The caller knows that #;OBJ must have occurred
because there are no errors and the parser isn't at EOF, yet
there is no parse tree. Then in lisp_parse we can loop on this
situation, and make adjustments elsewhere also.

So that iread continues to work, we must separate the
parser_eof condition from the lookahead token. Under iread,
we were clearing the token in prime_parser_post, but that
was having the side effect of making the parser look like
it is in EOF. We now preserve the EOF indication in a flag,
so we can manipulate the token.

* parser.h (struct parser): new member, eof.

* parser.c (parser_common_init): Initialize new eof flag
in parser structure to zero.
(prime_parser_post): Set the eof flag if the parser's most
recent token is zero.
(lisp_parse_impl): Call the parser repeatedly while there
are no errors, and no EOF, yet no object has been produced.
This indicates that a #; erasure has been processed.
(read_eval_stream): Restructure the logic here for
clarity. Do not break the loop if error_val was returned
from the parser, but there are no errors, and the parser isn't
at EOF. This is behavior is probably redundant with respect
to the loop in lisp_parse_impl.
(read_eval_ret_last): Bugfixes here. Pass an error indicating
value down to lisp_parse, like in read_eval_stream and
make the logic similar.
(parser_eof): Just return an indication based no the
eof flag.

* parser.y (hash_semis_n_expr, hash_semis_i_expr,
ignored_i_exprs, ignored_n_exprs): Grammar rules removed.
(hash_semi_or_n_expr, hash_semi_or_i_expr): New grammar
rules.
(spec): Retarget SECRET_ESCAPE_E and SECRET_ESCAPE_I
cases to new rules.
(parse): Clear eof flag to zero.

1 files changed, 1 insertions, 0 deletions

diff --git a/parser.h b/parser.h
index 6980e0f4..658178c7 100644
--- a/parser.h
+++ b/parser.h
@@ -50,6 +50,7 @@ struct parser {
   val parser;
   cnum lineno;
   int errors;
+  int eof;
   val stream;
   val name;
   val prepared_msg;