[WIP] Streaming CSS parser

third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp b/third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp
index 26de5664a0ae380942d1bbbf6d78b3d8d6c6a11b..9e1842beb9e8d6ba5c7d6c021e4d3de002bd84cd 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSTokenizer.cpp
@@ -9,70 +9,55 @@ namespace blink {
 }
 
 #include "core/css/parser/CSSParserIdioms.h"
-#include "core/css/parser/CSSParserObserverWrapper.h"
+#include "core/css/parser/CSSParserObserver.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "wtf/text/CharacterNames.h"
 
 namespace blink {
 
-CSSTokenizer::CSSTokenizer(const String& string) : m_input(string) {
-  // According to the spec, we should perform preprocessing here.
-  // See: http://dev.w3.org/csswg/css-syntax/#input-preprocessing
-  //
-  // However, we can skip this step since:
-  // * We're using HTML spaces (which accept \r and \f as a valid white space)
-  // * Do not count white spaces
-  // * CSSTokenizerInputStream::nextInputChar() replaces NULLs for replacement
-  //   characters
-
-  if (string.isEmpty())
-    return;
+// We handle input preprocessing substitutions during tokenization:
+// * We also accept \r and \f as white space
+// * CSSTokenizerInputStream::nextInputChar() replaces NULLs for replacement
+//   characters
+
+CSSTokenizer::CSSTokenizer(const String& string, size_t startOffset)
+    : m_input(string) {
+  m_input.advance(startOffset);

[Charlie Harrison, 2017/01/09 21:35:07]

It looks like advance() does not change the underlying length. Should I be
worried at the reserveInitialCapacity() call below?

+}
+
+CSSParserTokenRange CSSTokenizer::tokenRange() {
+  if (m_finishedTokenizing)
+    return m_tokens;
 
-  // To avoid resizing we err on the side of reserving too much space.
-  // Most strings we tokenize have about 3.5 to 5 characters per token.
-  m_tokens.reserveInitialCapacity(string.length() / 3);

[Charlie Harrison, 2017/01/09 21:35:07]

w000t!

+  // Try to avoid resizing the Vector by reserving space.
+  m_tokens.reserveInitialCapacity(m_input.length() / 3);
 
   while (true) {
     CSSParserToken token = nextToken();
     if (token.type() == CommentToken)
       continue;
     if (token.type() == EOFToken)
-      return;
+      break;
     m_tokens.push_back(token);
   }
+  m_finishedTokenizing = true;
+  return m_tokens;
 }
 
-CSSTokenizer::CSSTokenizer(const String& string,
-                           CSSParserObserverWrapper& wrapper)
-    : m_input(string) {
-  if (string.isEmpty())
+void CSSTokenizer::tokenizeSingle() {

[Charlie Harrison, 2017/01/09 21:35:07]

Maybe tokenizeSingle could return something useful, like whether we're finished
tokenizing, or maybe the last token tokenized?

+  if (m_finishedTokenizing)
     return;
-
-  unsigned offset = 0;
   while (true) {
     CSSParserToken token = nextToken();
+    if (token.type() == CommentToken)
+      continue;
     if (token.type() == EOFToken)
-      break;
-    if (token.type() == CommentToken) {
-      wrapper.addComment(offset, m_input.offset(), m_tokens.size());
-    } else {
+      m_finishedTokenizing = true;
+    else
       m_tokens.push_back(token);
-      wrapper.addToken(offset);
-    }
-    offset = m_input.offset();
+    return;
   }
-
-  wrapper.addToken(offset);
-  wrapper.finalizeConstruction(m_tokens.begin());
-}
-
-CSSParserTokenRange CSSTokenizer::tokenRange() {
-  return m_tokens;
-}
-
-unsigned CSSTokenizer::tokenCount() {
-  return m_tokens.size();
 }
 
 static bool isNewLine(UChar cc) {
@@ -681,4 +666,196 @@ StringView CSSTokenizer::registerString(const String& string) {
   return string;
 }
 
+bool isCSSIdentCharacter(UChar cc) {
+  return isASCIIAlphanumeric(cc) || cc == '-' || cc == '_' || cc > 128;
+}
+
+// If the next character is an ASCII insensitive match for cc, skips that.
+// Otherwise, skips the remaining ident characters.
+bool CSSTokenizer::skipIdentCharacters(UChar cc) {
+  UChar nextChar = consume();
+  if (isASCIIAlphaCaselessEqual(nextChar, cc))

[Charlie Harrison, 2017/01/09 21:35:07]

Hm, this function has a compiler hint that the branch is likely to be true. I'm
worried that might lead to poor branch prediction. WDYT?

+    return true;
+  if (nextChar == '\\') {
+    if (m_input.peekWithoutReplacement(0) == '\n') {
+      m_input.advance();
+      return false;
+    }
+    if (isASCIIAlphaCaselessEqual(consumeEscape(), cc))
+      return true;
+  }
+  skipIdentCharacters();
+  return false;
+}
+
+void CSSTokenizer::skipIdentCharacters() {
+  while (true) {
+    UChar nextChar = m_input.peekWithoutReplacement(0);
+    if (nextChar == '\\') {
+      if (m_input.peekWithoutReplacement(1) == '\n') {
+        m_input.advance(2);
+        return;
+      }
+      m_input.advance();
+      consumeEscape();
+    }
+    if (!isCSSIdentCharacter(nextChar))
+      return;
+    m_input.advance();
+  }
+}
+
+void CSSTokenizer::skipToBlockEnd() {
+  DCHECK(!m_blockStack.isEmpty());
+  DCHECK_EQ(m_blockStack.back(), LeftBraceToken);
+  int nesting = 1;
+  do {
+    UChar nextChar = m_input.peekWithoutReplacement(0);
+
+    // url's are special as their error recovery doesn't match blocks.
+    // url(([{) is a single <bad-url-token>, while moo(([{) needs }])) to
+    // close the component value. We need enough tokenization logic to be
+    // able to identify urls.
+    // Technically we should handle our non-standard unicode range tokens
+    // but probably no one will encounter these cases.
+    if (isCSSIdentCharacter(nextChar) || nextChar == '\\') {
+      if (!skipIdentCharacters('u') || !skipIdentCharacters('r') ||
+          !skipIdentCharacters('l'))
+        continue;
+
+      if (m_input.peekWithoutReplacement(0) != '(') {
+        skipIdentCharacters();
+        continue;
+      }
+
+      skipWhitespaceAndComments();
+      UChar innerChar = m_input.nextInputChar();
+      if (innerChar == '"' || innerChar == '\'') {
+        nesting++;
+        m_blockStack.append(LeftParenthesisToken);
+        continue;
+      }
+      while (innerChar != ')' && innerChar != '\0') {
+        m_input.advance();
+        if (innerChar == '\\') {
+          if (m_input.peekWithoutReplacement(0) == '\n')
+            m_input.advance();
+          else
+            consumeEscape();
+        }
+        innerChar = m_input.nextInputChar();
+      }
+      m_input.advance();
+      continue;
+    }
+
+    m_input.advance();
+
+    switch (nextChar) {
+      case '/':
+        if (m_input.peekWithoutReplacement(0) == '*') {
+          m_input.advance();
+          consumeUntilCommentEndFound();
+        }
+        break;
+      case '"':
+      case '\'': {
+        while (true) {
+          UChar cc = m_input.peekWithoutReplacement(0);
+          m_input.advance(1);
+          if (cc == nextChar || isNewLine(cc))
+            break;
+          if (cc == '\\') {
+            // This is to handle escapes delimited by newlines
+            consumeEscape();
+            continue;
+          }
+          if (cc == '\0' && m_input.nextInputChar() == '\0')
+            return;  // EOF
+        }
+        break;
+      }
+      case '<':
+        // We need to handle this so <!--url( makes an url token
+        if (m_input.peekWithoutReplacement(0) == '!' &&
+            m_input.peekWithoutReplacement(1) == '-' &&
+            m_input.peekWithoutReplacement(2) == '-') {
+          m_input.advance(3);
+        }
+        break;
+      case '#':
+      case '@':
+        skipIdentCharacters();
+        break;
+      case '(':
+        nesting++;
+        m_blockStack.append(LeftParenthesisToken);
+        break;
+      case '[':
+        nesting++;
+        m_blockStack.append(LeftBracketToken);
+        break;
+      case '{':
+        nesting++;
+        m_blockStack.append(LeftBraceToken);
+        break;
+      case ')':
+        if (nesting && m_blockStack.back() == LeftParenthesisToken) {
+          nesting--;
+          m_blockStack.pop_back();
+        }
+        break;
+      case ']':
+        if (nesting && m_blockStack.back() == LeftBracketToken) {
+          nesting--;
+          m_blockStack.pop_back();
+        }
+        break;
+      case '}':
+        if (nesting && m_blockStack.back() == LeftBraceToken) {
+          nesting--;
+          m_blockStack.pop_back();
+        }
+        break;
+      case '\0':
+        if (m_input.nextInputChar() == '\0')
+          return;
+        skipIdentCharacters();
+        break;
+    }
+  } while (nesting);
+  m_tokens.pop_back();
+}
+
+void CSSTokenizer::skipComments() {
+  while (m_input.peekWithoutReplacement(0) == '/' &&
+         m_input.peekWithoutReplacement(1) == '*') {
+    m_input.advance(2);
+    consumeUntilCommentEndFound();
+  }
+}
+
+void CSSTokenizer::skipWhitespaceAndComments() {
+  while (true) {
+    m_input.advanceUntilNonWhitespace();
+    if (m_input.peekWithoutReplacement(0) == '/' &&
+        m_input.peekWithoutReplacement(1) == '*') {
+      m_input.advance(2);
+      consumeUntilCommentEndFound();
+    } else {
+      break;
+    }
+  }
+}
+
+void CSSTokenizer::yieldComments(CSSParserObserver& observer) {
+  while (m_input.peekWithoutReplacement(0) == '/' &&
+         m_input.peekWithoutReplacement(1) == '*') {
+    size_t startOffset = m_input.offset();
+    m_input.advance(2);
+    consumeUntilCommentEndFound();
+    observer.observeComment(startOffset, m_input.offset());
+  }
+}
+
 }  // namespace blink