Don't try to compile a pattern known to be in error

Regular expression patterns are parsed by the lexer/toker, and then
compiled by the regex compiler.  It is foolish to try to compile one
that the parser has rejected as syntactically bad; assumptions may be
violated and segfaults ensue.  This commit abandons all parsing
immediately if a pattern had errors in it.  A better solution would be
to flag this pattern as not to be compiled, and continue parsing other
things so as to find the most errors in a single attempt, but I don't
think it's worth the extra effort.

Making this change caused some misleading error messages in the test
suite to be replaced by better ones.

1 files changed, 9 insertions, 0 deletions

diff --git a/toke.c b/toke.c
index 383203aecf..880ac53b7d 100644
--- a/toke.c
+++ b/toke.c
@@ -5021,7 +5021,16 @@ Perl_yylex(pTHX)
 	    s = PL_bufend;
 	}
 	else {
+            int save_error_count = PL_error_count;
+
 	    s = scan_const(PL_bufptr);
+
+            /* Quit if this was a pattern and there were errors.  This prevents
+             * us from trying to regex compile a broken pattern, which could
+             * lead to segfaults, etc. */
+            if (PL_lex_inpat && PL_error_count > save_error_count) {
+                yyquit();
+            }
 	    if (*s == '\\')
 		PL_lex_state = LEX_INTERPCASEMOD;
 	    else