Fix incorrect asserts in scanner.

BUG=v8::1126
TEST=test/mjsunit/regress/regress-1126.js

Review URL: http://codereview.chromium.org/6459021

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6701 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/scanner.cc

@@ -76,7 +76,8 @@ void BufferedUC16CharacterStream::SlowPushBack(uc16 character) {
     buffer_end_ = buffer_ + kBufferSize;
     buffer_cursor_ = buffer_end_;
   }
-  ASSERT(pushback_limit_ > buffer_);
+  // Ensure that there is room for at least one pushback.
+  ASSERT(buffer_cursor_ > buffer_);
   ASSERT(pos_ > 0);
   buffer_[--buffer_cursor_ - buffer_] = character;
   if (buffer_cursor_ == buffer_) {
@@ -89,15 +90,17 @@ void BufferedUC16CharacterStream::SlowPushBack(uc16 character) {
 
 
 bool BufferedUC16CharacterStream::ReadBlock() {
+  buffer_cursor_ = buffer_;
   if (pushback_limit_ != NULL) {
-    buffer_cursor_ = buffer_;
+    // Leave pushback mode.
     buffer_end_ = pushback_limit_;
     pushback_limit_ = NULL;
-    ASSERT(buffer_cursor_ != buffer_end_);
-    return true;
+    // If there were any valid characters left at the
+    // start of the buffer, use those.
+    if (buffer_cursor_ < buffer_end_) return true;
+    // Otherwise read a new block.
   }
   unsigned length = FillBuffer(pos_, kBufferSize);
-  buffer_cursor_ = buffer_;
   buffer_end_ = buffer_ + length;
   return length > 0;
 }

test/mjsunit/regress/regress-1126.js

+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This should properly catch the exception from the setter triggered
+// by the loaded file, and it should not fail an assertion in debug mode.
+
+try {
+   eval('--');
+   assertUnreachable();
+} catch (e) {
+}