Re: Values from immediately preceding action blocks are no longer available in bison 1.50

[Paul Eggert]

> From: address@hidden
> Date: Fri, 11 Oct 2002 16:04:22 +0200 (MET DST)

> In bison 1.50 the following construct is no longer accepted:
> nonterm: TERMINAL
>   { $<field>$ = val; }
>   { code using $<field>2; }
>   more non terminals
>   ;

Thanks for your bug report.  I installed the following patch, which
should appear in the next Bison version.

2002-10-13  Paul Eggert  <address@hidden>

        Fix problem reported by Henrik Grubbstroem in
        <http://mail.gnu.org/pipermail/bug-bison/2002-October/001670.html>:
        "nonterm: { $$ = 123; } { $$ = $1; };" was wrongly rejected,
        because the Bison parser reads the second action before reducing
        the first one.
        * src/scan-gram.l (rule_length): New static var.
        Use it to keep track of the rule length in the scanner, since
        we can't expect the parser to be in lock-step sync with the scanner.
        (handle_action_dollar, handle_action_at): Use this var.
        * tests/actions.at (Exotic Dollars): Test for the problem.

Index: src/scan-gram.l
===================================================================
RCS file: /cvsroot/bison/bison/src/scan-gram.l,v
retrieving revision 1.25
diff -p -u -r1.25 scan-gram.l
--- src/scan-gram.l     11 Oct 2002 11:23:19 -0000      1.25
+++ src/scan-gram.l     13 Oct 2002 08:33:05 -0000
@@ -79,6 +79,14 @@ scanner_last_string_free (void)
 static int braces_level = 0;
 static int percent_percent_count = 0;
 
+/* Within well-formed rules, RULE_LENGTH is the number of values in
+   the current rule so far, which says where to find `$0' with respect
+   to the top of the stack.  It is not the same as the rule->length in
+   the case of mid rule actions.
+
+   Outside of well-formed rules, RULE_LENGTH has an undefined value.  */
+static int rule_length;
+
 static void handle_dollar PARAMS ((braced_code_t code_kind,
                                   char *cp, location_t location));
 static void handle_at PARAMS ((braced_code_t code_kind,
@@ -138,7 +146,7 @@ blanks   [ \t\f]+
   "%nonassoc"             return PERCENT_NONASSOC;
   "%nterm"                return PERCENT_NTERM;
   "%output"               return PERCENT_OUTPUT;
-  "%prec"                 return PERCENT_PREC;
+  "%prec"                 { rule_length--; return PERCENT_PREC; }
   "%printer"              return PERCENT_PRINTER;
   "%pure"[-_]"parser"     return PERCENT_PURE_PARSER;
   "%right"                return PERCENT_RIGHT;
@@ -153,14 +161,15 @@ blanks   [ \t\f]+
   "%yacc"                 return PERCENT_YACC;
 
   "="                     return EQUAL;
-  ":"                     return COLON;
-  "|"                     return PIPE;
+  ":"                     { rule_length = 0; return COLON; }
+  "|"                     { rule_length = 0; return PIPE; }
   ";"                     return SEMICOLON;
 
   {eols}      YY_LINES; YY_STEP;
   {blanks}    YY_STEP;
   {id}        {
     yylval->symbol = symbol_get (yytext, *yylloc);
+    rule_length++;
     return ID;
   }
 
@@ -262,6 +271,7 @@ blanks   [ \t\f]+
     YY_OBS_FINISH;
     yylval->string = last_string;
     yy_pop_state ();
+    rule_length++;
     return STRING;
   }
 
@@ -298,6 +308,7 @@ blanks   [ \t\f]+
                                    (unsigned char) last_string[1], *yylloc);
       YY_OBS_FREE;
       yy_pop_state ();
+      rule_length++;
       return ID;
     }
   }
@@ -451,6 +462,7 @@ blanks   [ \t\f]+
        yy_pop_state ();
        YY_OBS_FINISH;
        yylval->string = last_string;
+       rule_length++;
        return BRACED_CODE;
       }
   }
@@ -566,11 +578,6 @@ handle_action_dollar (char *text, locati
     }
   else if (('0' <= *cp && *cp <= '9') || *cp == '-')
     {
-      /* RULE_LENGTH is the number of values in the current rule so
-        far, which says where to find `$0' with respect to the top of
-        the stack.  It is not the same as the rule->length in the
-        case of mid rule actions.  */
-      int rule_length = symbol_list_length (current_rule->next);
       int n = strtol (cp, &cp, 10);
 
       if (n > rule_length)
@@ -653,11 +660,6 @@ handle_action_at (char *text, location_t
     }
   else if (('0' <= *cp && *cp <= '9') || *cp == '-')
     {
-      /* RULE_LENGTH is the number of values in the current rule so
-        far, which says where to find `$0' with respect to the top of
-        the stack.  It is not the same as the rule->length in the
-        case of mid rule actions.  */
-      int rule_length = symbol_list_length (current_rule->next);
       int n = strtol (cp, &cp, 10);
 
       if (n > rule_length)
Index: tests/actions.at
===================================================================
RCS file: /cvsroot/bison/bison/tests/actions.at,v
retrieving revision 1.14
diff -p -u -r1.14 actions.at
--- tests/actions.at    30 Jul 2002 11:56:44 -0000      1.14
+++ tests/actions.at    13 Oct 2002 08:33:05 -0000
@@ -103,18 +103,18 @@ AT_DATA([[input.y]],
   int val;
 };
 
-%type <val> a_1 a_2 a_4 a_5
+%type <val> a_1 a_2 a_5
             sum_of_the_five_previous_values
 
 %%
-exp: a_1 a_2 { $<val>$ = 3; } a_4 a_5 sum_of_the_five_previous_values
+exp: a_1 a_2 { $<val>$ = 3; } { $<val>$ = $<val>3 + 1; } a_5
+     sum_of_the_five_previous_values
     {
        printf ("%d\n", $6);
     }
 ;
 a_1: { $$ = 1; };
 a_2: { $$ = 2; };
-a_4: { $$ = 4; };
 a_5: { $$ = 5; };
 
 sum_of_the_five_previous_values: