reader: reject rules on YYEOF

[Akim Demaille]

commit dd6ca199276506c4902a993b863fa10414a90178
Author: Akim Demaille <akim.demaille@gmail.com>
Date:   Sat Sep 10 14:04:11 2022 +0200

    reader: reject rules on YYEOF
    
    We crashed when rules were given on YYEOF.
    Reported by Han Zheng.
    Fixes https://github.com/akimd/bison/issues/92.
    
    * src/reader.c (check_and_convert_grammar): Make sure YYEOF is not
    an nterm.
    * tests/input.at (Rule for YYEOF): New.

diff --git a/src/reader.c b/src/reader.c
index baa5d803..3d60ab36 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -954,6 +954,10 @@ check_and_convert_grammar (void)
   if (!eoftoken)
     {
       eoftoken = symbol_get ("YYEOF", empty_loc);
+      if (eoftoken->content->class == nterm_sym)
+        complain (&eoftoken->location, complaint,
+                  _("rule given for %s, which is a token"),
+                  eoftoken->tag);
       eoftoken->content->class = token_sym;
       eoftoken->content->number = 0;
       /* Value specified by POSIX.  */
diff --git a/tests/input.at b/tests/input.at
index f76000be..5cacb066 100644
--- a/tests/input.at
+++ b/tests/input.at
@@ -1888,6 +1888,38 @@ AT_SETUP([Duplicate %start symbol])
 AT_CLEANUP
 
 
+## ---------------- ##
+## Rule for YYEOF.  ##
+## ---------------- ##
+
+AT_SETUP([Rule for YYEOF])
+
+# We crashed when rules were given on YYEOF.
+# https://github.com/akimd/bison/issues/92.
+
+AT_DATA([input1.y],
+[[%%
+start: YYEOF;
+YYEOF: 'x';
+]])
+
+AT_BISON_CHECK([input1.y], [1], [],
+[[input1.y:3.1-5: error: rule given for YYEOF, which is a token
+]])
+
+# This is ok, YYEOF is not special.
+AT_DATA([input2.y],
+[[%token MYEOF 0
+%%
+start: YYEOF;
+YYEOF: 'x';
+]])
+
+AT_BISON_CHECK([input2.y])
+
+AT_CLEANUP
+
+
 ## --------------------- ##
 ## %prec takes a token.  ##
 ## --------------------- ##