[parser] Use Back2() where appropriate.

test/cctest/parsing/test-scanner.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Tests v8::internal::Scanner. Note that presently most unit tests for the
 // Scanner are in cctest/test-parsing.cc, rather than here.
 
 #include "src/handles-inl.h"
 #include "src/parsing/scanner-character-streams.h"
 #include "src/parsing/scanner.h"
 #include "src/unicode-cache.h"
 #include "test/cctest/cctest.h"
 
 using namespace v8::internal;
 
 namespace {
 
 const char src_simple[] = "function foo() { var x = 2 * a() + b; }";
 
 std::unique_ptr<Scanner> make_scanner(const char* src) {
   std::unique_ptr<Scanner> scanner(new Scanner(new UnicodeCache()));
   scanner->Initialize(ScannerStream::ForTesting(src).release());
   return scanner;
 }
 
 }  // anonymous namespace
 
+// DCHECK_TOK checks token equality, but by checking for equality of the token
+// names. That should have the same result, but has much nicer error messaages.
+#define DCHECK_TOK(a, b) DCHECK_EQ(Token::Name(a), Token::Name(b))
+
 TEST(Bookmarks) {
   // Scan through the given source and record the tokens for use as reference
   // below.
   std::vector<Token::Value> tokens;
   {
     auto scanner = make_scanner(src_simple);
     do {
       tokens.push_back(scanner->Next());
     } while (scanner->current_token() != Token::EOS);
   }
 
   // For each position:
   // - Scan through file,
   // - set a bookmark once the position is reached,
   // - scan a bit more,
   // - reset to the bookmark, and
   // - scan until the end.
   // At each step, compare to the reference token sequence generated above.
   for (size_t bookmark_pos = 0; bookmark_pos < tokens.size(); bookmark_pos++) {
     auto scanner = make_scanner(src_simple);
     Scanner::BookmarkScope bookmark(scanner.get());
 
     for (size_t i = 0; i < std::min(bookmark_pos + 10, tokens.size()); i++) {
       if (i == bookmark_pos) {
         bookmark.Set();
       }
-      DCHECK_EQ(tokens[i], scanner->Next());
+      DCHECK_TOK(tokens[i], scanner->Next());
     }
 
     bookmark.Apply();
     for (size_t i = bookmark_pos; i < tokens.size(); i++) {
-      DCHECK_EQ(tokens[i], scanner->Next());
+      DCHECK_TOK(tokens[i], scanner->Next());
     }
   }
 }
+
+TEST(AllThePushbacks) {
+  const struct {
+    const char* src;
+    const Token::Value tokens[5];  // Large enough for any of the test cases.
+  } test_cases[] = {
+      {"<-x", {Token::LT, Token::SUB, Token::IDENTIFIER, Token::EOS}},
+      {"<!x", {Token::LT, Token::NOT, Token::IDENTIFIER, Token::EOS}},
+      {"<!-x",
+       {Token::LT, Token::NOT, Token::SUB, Token::IDENTIFIER, Token::EOS}},
+      {"<!-- xx -->\nx", {Token::IDENTIFIER, Token::EOS}},
+  };
+
+  for (const auto& test_case : test_cases) {
+    auto scanner = make_scanner(test_case.src);
+    for (size_t i = 0; test_case.tokens[i] != Token::EOS; i++) {
+      DCHECK_TOK(test_case.tokens[i], scanner->Next());
+    }
+    DCHECK_TOK(Token::EOS, scanner->Next());
+  }
+}