From 4d7370cb4fe960032afd4a42293b6d55e02237fe Mon Sep 17 00:00:00 2001
From: "Joel E. Denny" <jdenny@ces.clemson.edu>
Date: Sun, 20 Aug 2006 03:10:18 +0000
Subject: [PATCH] Allow %start after the first rule. * src/reader.c
 (grammar_current_rule_begin): Don't set the start symbol when parsing the
 first rule. (check_and_convert_grammar): Search for it here after all grammar
 declarations have been parsed.  Skip midrules, which have dummy LHS
 nonterminals. * src/symtab.c (symbol_is_dummy): New function. * src/symtab.h
 (symbol_is_dummy): Declare it. * tests/input.at (%start after first rule):
 New test.

---
 ChangeLog      | 12 ++++++++++++
 src/reader.c   | 24 +++++++++++++++++-------
 src/symtab.c   |  5 +++++
 src/symtab.h   |  3 +++
 tests/input.at | 21 +++++++++++++++++++++
 5 files changed, 58 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 3cc5679f..f8867cbc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2006-08-19  Joel E. Denny  <jdenny@ces.clemson.edu>
+
+	Allow %start after the first rule.
+	* src/reader.c (grammar_current_rule_begin): Don't set the start symbol
+	when parsing the first rule.
+	(check_and_convert_grammar): Search for it here after all grammar
+	declarations have been parsed.  Skip midrules, which have dummy LHS
+	nonterminals.
+	* src/symtab.c (symbol_is_dummy): New function.
+	* src/symtab.h (symbol_is_dummy): Declare it.
+	* tests/input.at (%start after first rule): New test.
+
 2006-08-18  Joel E. Denny  <jdenny@ces.clemson.edu>
 
 	Redo some of the previous commit: add back the ability to use
diff --git a/src/reader.c b/src/reader.c
index 5084618f..d380d047 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -225,13 +225,6 @@ static symbol_list *previous_rule_end = NULL;
 void
 grammar_current_rule_begin (symbol *lhs, location loc)
 {
-  if (!start_flag)
-    {
-      startsymbol = lhs;
-      startsymbol_location = loc;
-      start_flag = true;
-    }
-
   /* Start a new rule and record its lhs.  */
   ++nrules;
   previous_rule_end = grammar_end;
@@ -607,6 +600,23 @@ check_and_convert_grammar (void)
       endtoken->user_token_number = 0;
     }
 
+  /* Find the start symbol if no %start.  */
+  if (!start_flag)
+    {
+      symbol_list *node;
+      for (node = grammar;
+           node != NULL && symbol_is_dummy (node->sym);
+           node = node->next)
+        {
+          for (node = node->next;
+               node != NULL && node->sym != NULL;
+               node = node->next)
+            ;
+        }
+      assert (node != NULL);
+      grammar_start_symbol_set (node->sym, node->sym->location);
+    }
+
   /* Insert the initial rule, whose line is that of the first rule
      (not that of the start symbol):
 
diff --git a/src/symtab.c b/src/symtab.c
index 37677ed7..40ba0bee 100644
--- a/src/symtab.c
+++ b/src/symtab.c
@@ -615,6 +615,11 @@ dummy_symbol_get (location loc)
   return sym;
 }
 
+bool
+symbol_is_dummy (const symbol *sym)
+{
+  return sym->tag[0] == '@';
+}
 
 /*-------------------.
 | Free the symbols.  |
diff --git a/src/symtab.h b/src/symtab.h
index 1a3ada4c..647a9e4c 100644
--- a/src/symtab.h
+++ b/src/symtab.h
@@ -133,6 +133,9 @@ symbol *symbol_get (const char *key, location loc);
    Its name cannot conflict with the user's names.  */
 symbol *dummy_symbol_get (location loc);
 
+/** Is this a dummy nonterminal?  */
+bool symbol_is_dummy (const symbol *sym);
+
 /** Declare the new symbol \c sym.  Make it an alias of \c symval.  */
 void symbol_make_alias (symbol *sym, symbol *symval, location loc);
 
diff --git a/tests/input.at b/tests/input.at
index 0fce2dd1..ce1c777a 100644
--- a/tests/input.at
+++ b/tests/input.at
@@ -537,3 +537,24 @@ input.y:20.1: syntax error, unexpected end of file, expecting ;
 ]])
 
 AT_CLEANUP
+
+
+## ------------------------- ##
+## %start after first rule.  ##
+## ------------------------- ##
+
+AT_SETUP([%start after first rule])
+
+# Bison once complained that a %start after the first rule was a redeclaration
+# of the start symbol.
+
+AT_DATA([input.y],
+[[%%
+false_start: ;
+start: false_start ;
+%start start;
+]])
+
+AT_CHECK([bison -o input.c input.y])
+
+AT_CLEANUP
-- 
2.45.2