From 27cb5b590124894edc3e4bee11737972e56d2dbe Mon Sep 17 00:00:00 2001
From: Akim Demaille <demaille@gostai.com>
Date: Mon, 18 Aug 2008 21:31:06 +0200
Subject: [PATCH] yychar cannot be empty in yyerrlab.

	* TODO (yychar == yyempty_): New.
	* data/lalr1.cc: Remove the handling of this case.
	This eases forthcoming changes related to yychar and yytranslate.
---
 ChangeLog     |  7 +++++++
 TODO          | 16 ++++++++++++++++
 data/lalr1.cc | 25 +++++++++++++------------
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 17023e24..e8e8ac2b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2008-11-11  Akim Demaille  <demaille@gostai.com>
+
+	yychar cannot be empty in yyerrlab.
+	* TODO (yychar == yyempty_): New.
+	* data/lalr1.cc: Remove the handling of this case.
+	This eases forthcoming changes related to yychar and yytranslate.
+
 2008-11-11  Akim Demaille  <demaille@gostai.com>
 
 	Bench: syntactic sugar for %define/#define.
diff --git a/TODO b/TODO
index 7b473094..918ca350 100644
--- a/TODO
+++ b/TODO
@@ -54,6 +54,22 @@ what it should look like.  For instance what follows crashes.
     return yyparse ();
   }
 
+** yychar == yyempty_
+The code in yyerrlab reads:
+
+      if (yychar <= YYEOF)
+	{
+	  /* Return failure if at end of input.  */
+	  if (yychar == YYEOF)
+	    YYABORT;
+	}
+
+There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF.
+But I can't produce the situation where yychar is YYEMPTY here, is it
+really possible?  The test suite does not exercise this case.
+
+This shows that it would be interesting to manage to install skeleton
+coverage analysis to the test suite.
 
 * Header guards
 
diff --git a/data/lalr1.cc b/data/lalr1.cc
index 4915caa2..8c5b3345 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -1281,18 +1281,19 @@ m4_ifdef([b4_lex_param], [, ]b4_lex_param))[;
     if (yyerrstatus_ == 3)
       {
 	/* If just tried and failed to reuse lookahead token after an
-	 error, discard it.  */
-
-	if (yychar <= yyeof_)
-	  {
-            /* Return failure if at end of input.  */
-            if (yychar == yyeof_)
-              YYABORT;
-	  }
-	else
-	  {
-	    yy_destroy_ ("Error: discarding", yyla);
-	    yychar = yyempty_;
+           error, discard it.  */
+
+        /* Return failure if at end of input.  */
+        if (yychar == yyeof_)
+          YYABORT;
+        else
+          {]b4_assert_if([
+            // Previous version of this code was ready to handle
+            // yychar == yyempty_ (actually yychar <= yyeof_).  Can it
+            // really be triggered?
+            assert (yychar != yyempty_);])[
+            yy_destroy_ ("Error: discarding", yyla);
+            yychar = yyempty_;
 	  }
       }
 
-- 
2.47.2