Bug 773296 - Part 11: Give nsCSSParser and nsCSSScanner the ability to save/restore their current input state. r=dbaron

This adds functions to nsCSSParser and nsCSSScanner that let us save the
current input position (and corresponding information like line/column
number) and parser pushback, and be able to restore it later.  We'll use
this when rewinding the scanner after we first encounter a property with
a variable reference and go back to reparse it as a token stream.

layout/style/nsCSSParser.cpp

@@ -64,6 +64,12 @@ typedef void (* RuleAppendFunc) (css::Rule* aRule, void* aData);
 static void AssignRuleToPointer(css::Rule* aRule, void* aPointer);
 static void AppendRuleToSheet(css::Rule* aRule, void* aParser);
 
+struct CSSParserInputState {
+  nsCSSScannerPosition mPosition;
+  nsCSSToken mToken;
+  bool mHavePushBack;
+};
+
 // Your basic top-down recursive descent style parser
 // The exposed methods and members of this class are precisely those
 // needed by nsCSSParser, far below.
@@ -289,6 +295,18 @@ protected:
     return mScanner->IsSVGMode();
   }
 
+  /**
+   * Saves the current input state, which includes any currently pushed
+   * back token, and the current position of the scanner.
+   */
+  void SaveInputState(CSSParserInputState& aState);
+
+  /**
+   * Restores the saved input state by pushing back any saved pushback
+   * token and calling RestoreSavedPosition on the scanner.
+   */
+  void RestoreSavedInputState(const CSSParserInputState& aState);
+
   bool GetToken(bool aSkipWS);
   void UngetToken();
   bool GetNextTokenLocation(bool aSkipWS, uint32_t *linenum, uint32_t *colnum);
@@ -7144,6 +7162,22 @@ static const nsCSSProperty kOutlineRadiusIDs[] = {
   eCSSProperty__moz_outline_radius_bottomLeft
 };
 
+void
+CSSParserImpl::SaveInputState(CSSParserInputState& aState)
+{
+  aState.mToken = mToken;
+  aState.mHavePushBack = mHavePushBack;
+  mScanner->SavePosition(aState.mPosition);
+}
+
+void
+CSSParserImpl::RestoreSavedInputState(const CSSParserInputState& aState)
+{
+  mToken = aState.mToken;
+  mHavePushBack = aState.mHavePushBack;
+  mScanner->RestoreSavedPosition(aState.mPosition);
+}
+
 bool
 CSSParserImpl::ParseProperty(nsCSSProperty aPropID)
 {

layout/style/nsCSSScanner.cpp

@@ -495,6 +495,32 @@ nsCSSScanner::Backup(uint32_t n)
 #endif
 }
 
+void
+nsCSSScanner::SavePosition(nsCSSScannerPosition& aState)
+{
+  aState.mOffset = mOffset;
+  aState.mLineNumber = mLineNumber;
+  aState.mLineOffset = mLineOffset;
+  aState.mTokenLineNumber = mTokenLineNumber;
+  aState.mTokenLineOffset = mTokenLineOffset;
+  aState.mTokenOffset = mTokenOffset;
+  aState.mInitialized = true;
+}
+
+void
+nsCSSScanner::RestoreSavedPosition(const nsCSSScannerPosition& aState)
+{
+  MOZ_ASSERT(aState.mInitialized, "have not saved state");
+  if (aState.mInitialized) {
+    mOffset = aState.mOffset;
+    mLineNumber = aState.mLineNumber;
+    mLineOffset = aState.mLineOffset;
+    mTokenLineNumber = aState.mTokenLineNumber;
+    mTokenLineOffset = aState.mTokenLineOffset;
+    mTokenOffset = aState.mTokenOffset;
+  }
+}
+
 /**
  * Skip over a sequence of whitespace characters (vertical or
  * horizontal) starting at the current read position.

layout/style/nsCSSScanner.h

@@ -156,6 +156,22 @@ struct nsCSSToken {
   void AppendToString(nsString& aBuffer) const;
 };
 
+// Represents an nsCSSScanner's saved position in the input buffer.
+class nsCSSScannerPosition {
+  friend class nsCSSScanner;
+public:
+  nsCSSScannerPosition() : mInitialized(false) { }
+
+private:
+  uint32_t mOffset;
+  uint32_t mLineNumber;
+  uint32_t mLineOffset;
+  uint32_t mTokenLineNumber;
+  uint32_t mTokenLineOffset;
+  uint32_t mTokenOffset;
+  bool mInitialized;
+};
+
 // nsCSSScanner tokenizes an input stream using the CSS2.1 forward
 // compatible tokenization rules.  Used internally by nsCSSParser;
 // not available for use by other code.
@@ -236,6 +252,12 @@ class nsCSSScanner {
   bool IsRecording() const;
 #endif
 
+  // Stores the current scanner offset into the specified object.
+  void SavePosition(nsCSSScannerPosition& aState);
+
+  // Resets the scanner offset to a position saved by SavePosition.
+  void RestoreSavedPosition(const nsCSSScannerPosition& aState);
+
   enum EOFCharacters {
     eEOFCharacters_None =                    0x0000,