Fix a longstanding bug uncovered by bro-0.9a9/src/parse.y, which I

got from <http://bro-ids.org/download.html>.  The bug is that
when two actions appeared in succession, the second one was
scanned before the first one was added to the grammar rule
as a midrule action.  Bison then output the incorrect warning
"parse.y:905.17-906.36: warning: unused value: $3".
* src/parse-gram.y (BRACED_CODE, action): These are no longer
associated with a value.
(rhs): Don't invoke grammar_current_rule_action_append.
(action): Invoke it here instead.
* src/reader.c (grammar_midrule_action): Now extern.
(grammar_current_rule_action_append): Don't invoke
grammar_midrule_action; that is now the scanner's job.
* src/reader.h (last_string, last_braced_code_loc):
(grammar_midrule_action): New decls.
* src/scan-gram.l (last_string): Now extern, sigh.
(last_braced_code_loc): New extern variable.
(<INITIAL>"{"): Invoke grammar_midrule_action if the current
rule already has an action.
(<SC_BRACED_CODE>"}"): Set last_braced_code_loc before returning.
* tests/input.at (AT_CHECK_UNUSED_VALUES):
Add some tests to check that the above changes fixed the bug.

ChangeLog

@@ -1,3 +1,28 @@
+2006-01-29  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Fix a longstanding bug uncovered by bro-0.9a9/src/parse.y, which I
+	got from <http://bro-ids.org/download.html>.  The bug is that
+	when two actions appeared in succession, the second one was
+	scanned before the first one was added to the grammar rule
+	as a midrule action.  Bison then output the incorrect warning
+	"parse.y:905.17-906.36: warning: unused value: $3".
+	* src/parse-gram.y (BRACED_CODE, action): These are no longer
+	associated with a value.
+	(rhs): Don't invoke grammar_current_rule_action_append.
+	(action): Invoke it here instead.
+	* src/reader.c (grammar_midrule_action): Now extern.
+	(grammar_current_rule_action_append): Don't invoke
+	grammar_midrule_action; that is now the scanner's job.
+	* src/reader.h (last_string, last_braced_code_loc):
+	(grammar_midrule_action): New decls.
+	* src/scan-gram.l (last_string): Now extern, sigh.
+	(last_braced_code_loc): New extern variable.
+	(<INITIAL>"{"): Invoke grammar_midrule_action if the current
+	rule already has an action.
+	(<SC_BRACED_CODE>"}"): Set last_braced_code_loc before returning.
+	* tests/input.at (AT_CHECK_UNUSED_VALUES):
+	Add some tests to check that the above changes fixed the bug.
+
 2006-01-27  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* src/reader.c (symbol_should_be_used): Renamed from symbol_typed_p.

src/parse-gram.y

@@ -176,7 +176,6 @@ static int current_prec = 0;
 	      "%parse-param {...}"
 	      "%printer {...}"
 	      "%union {...}"
-	      BRACED_CODE action
 	      PROLOGUE EPILOGUE
 %printer { fprintf (stderr, "\"%s\"", $$); }
 	      STRING string_content
@@ -187,7 +186,6 @@ static int current_prec = 0;
 	      "%parse-param {...}"
 	      "%printer {...}"
 	      "%union {...}"
-	      BRACED_CODE action
 	      PROLOGUE EPILOGUE
 %type <uniqstr> TYPE
 %printer { fprintf (stderr, "<%s>", $$); } TYPE
@@ -430,7 +428,6 @@ rhs:
 | rhs symbol
     { grammar_current_rule_symbol_append ($2, @2); }
 | rhs action
-    { grammar_current_rule_action_append ($2, @2); }
 | rhs "%prec" symbol
     { grammar_current_rule_prec_set ($3, @3); }
 | rhs "%dprec" INT
@@ -444,9 +441,21 @@ symbol:
 | string_as_id    { $$ = $1; }
 ;
 
+/* Handle the semantics of an action specially, with a mid-rule
+   action, so that grammar_current_rule_action_append is invoked
+   immediately after the braced code is read by the scanner.
+
+   This implementation relies on the LALR(1) parsing algorithm.
+   If grammar_current_rule_action_append were executed in a normal
+   action for this rule, then when the input grammar contains two
+   successive actions, the scanner would have to read both actions
+   before reducing this rule.  That wouldn't work, since the scanner
+   relies on all preceding input actions being processed by
+   grammar_current_rule_action_append before it scans the next
+   action.  */
 action:
+    { grammar_current_rule_action_append (last_string, last_braced_code_loc); }
   BRACED_CODE
-    { $$ = $1; }
 ;
 
 /* A string used as an ID: quote it.  */

src/reader.c

@@ -300,7 +300,7 @@ grammar_current_rule_end (location loc)
 | rule.                                                              |
 `-------------------------------------------------------------------*/
 
-static void
+void
 grammar_midrule_action (void)
 {
   /* Since the action was written out with this rule's number, we must
@@ -394,14 +394,13 @@ grammar_current_rule_symbol_append (symbol *sym, location loc)
   grammar_symbol_append (sym, loc);
 }
 
-/* Attach an ACTION to the current rule.  If needed, move the previous
+/* Attach an ACTION to the current rule.  */
-   action as a mid-rule action.  */
 
 void
 grammar_current_rule_action_append (const char *action, location loc)
 {
-  if (current_rule->action)
+  /* There's no need to invoke grammar_midrule_action here, since the
-    grammar_midrule_action ();
+     scanner already did it if necessary.  */
   current_rule->action = action;
   current_rule->action_location = loc;
 }

src/reader.h

@@ -1,6 +1,7 @@
 /* Input parser for Bison
 
-   Copyright (C) 2000, 2001, 2002, 2003, 2005 Free Software Foundation, Inc.
+   Copyright (C) 2000, 2001, 2002, 2003, 2005, 2006 Free Software
+   Foundation, Inc.
 
    This file is part of Bison, the GNU Compiler Compiler.
 
@@ -38,6 +39,8 @@ typedef struct merger_list
 extern FILE *gram_in;
 extern int gram__flex_debug;
 extern boundary scanner_cursor;
+extern char *last_string;
+extern location last_braced_code_loc;
 extern int max_left_semantic_context;
 void scanner_initialize (void);
 void scanner_free (void);
@@ -63,6 +66,7 @@ void grammar_start_symbol_set (symbol *sym, location loc);
 void prologue_augment (const char *prologue, location loc);
 void grammar_current_rule_begin (symbol *lhs, location loc);
 void grammar_current_rule_end (location loc);
+void grammar_midrule_action (void);
 void grammar_current_rule_prec_set (symbol *precsym, location loc);
 void grammar_current_rule_dprec_set (int dprec, location loc);
 void grammar_current_rule_merge_set (uniqstr name, location loc);

src/scan-gram.l

@@ -87,8 +87,11 @@ static size_t no_cr_read (FILE *, char *, size_t);
 static struct obstack obstack_for_string;
 
 /* A string representing the most recently saved token.  */
-static char *last_string;
+char *last_string;
 
+/* The location of the most recently saved token, if it was a
+   BRACED_CODE token; otherwise, this has an unspecified value.  */
+location last_braced_code_loc;
 
 #define STRING_GROW   \
   obstack_grow (&obstack_for_string, yytext, yyleng)
@@ -289,6 +292,8 @@ splice	 (\\[ \f\t\v]*\n)*
 
   /* Code in between braces.  */
   "{" {
+    if (current_rule->action)
+      grammar_midrule_action ();
     STRING_GROW;
     token_type = BRACED_CODE;
     braces_level = 0;
@@ -618,6 +623,7 @@ splice	 (\\[ \f\t\v]*\n)*
 	loc->start = code_start;
 	val->chars = last_string;
 	increment_rule_length (*loc);
+	last_braced_code_loc = *loc;
 	BEGIN INITIAL;
 	return token_type;
       }

tests/input.at

@@ -151,15 +151,21 @@ input.y:6.3-36: warning: unused value: $4
 input.y:6.3-36: warning: unused value: $5
 ])
 
-# AT_CHECK_UNUSED_VALUES([INT { $$ } { $$ = $2 } { }],
+AT_CHECK_UNUSED_VALUES([INT INT { } { $$ = $1 + $2; }])
-# [input.y:6.3-36: warning: unset value: $$
-# input.y:6.3-36: warning: unused value: $1
-# input.y:6.3-36: warning: unused value: $3
-# input.y:6.3-36: warning: unused value: $4
-# input.y:6.3-36: warning: unused value: $5
-# ])
 
-AT_CHECK_UNUSED_VALUES([INT { $$ = $1 } INT { $$ = $2 + $3 } INT { $$ = $4 + $5 }])
+AT_CHECK_UNUSED_VALUES([INT INT { $<integer>$ = 1; } { $$ = $1 + $2; }],
+[input.y:6.3-48: warning: unused value: $3
+])
+
+AT_CHECK_UNUSED_VALUES([INT INT { $$; } { $$ = $3; } { }],
+[input.y:6.3-34: warning: unset value: $$
+input.y:6.3-34: warning: unused value: $1
+input.y:6.3-34: warning: unused value: $2
+input.y:6.3-34: warning: unused value: $4
+])
+
+AT_CHECK_UNUSED_VALUES(
+  [INT { $$ = $1; } INT { $$ = $2 + $3; } INT { $$ = $4 + $5; }])