Allow ParseAndAppendEscape to fail when the stream does not contain an escape, and make callers handle this failure appropriately. This changes our behavior when backslash immediately precedes end-of-stream. (Bug 384672, patch 3) r=bzbarsky

layout/style/nsCSSScanner.cpp

@@ -971,7 +971,11 @@ nsCSSScanner::NextURL(nsCSSToken& aToken)
     ch = Read();
     if (ch < 0) break;
     if (ch == CSS_ESCAPE) {
-      ParseAndAppendEscape(ident, PR_FALSE);
+      if (!ParseAndAppendEscape(ident, PR_FALSE)) {
+        ok = PR_FALSE;
+        Pushback(ch);
+        break;
+      }
     } else if (IsWhitespace(ch)) {
       // Whitespace is allowed at the end of the URL
       EatWhiteSpace();
@@ -1002,13 +1006,16 @@ nsCSSScanner::NextURL(nsCSSToken& aToken)
 }
 
 
-void
+/**
+ * Returns whether an escape was succesfully parsed; if it was not,
+ * the backslash needs to be its own symbol token.
+ */
+PRBool
 nsCSSScanner::ParseAndAppendEscape(nsString& aOutput, PRBool aInString)
 {
   PRInt32 ch = Peek();
   if (ch < 0) {
-    aOutput.Append(CSS_ESCAPE);
-    return;
+    return PR_FALSE;
   }
   if (IsHexDigit(ch)) {
     PRInt32 rv = 0;
@@ -1054,7 +1061,7 @@ nsCSSScanner::ParseAndAppendEscape(nsString& aOutput, PRBool aInString)
       if (IsWhitespace(ch))
         Pushback(ch);
     }
-    return;
+    return PR_TRUE;
   } 
   // "Any character except a hexidecimal digit can be escaped to
   // remove its special meaning by putting a backslash in front"
@@ -1063,6 +1070,8 @@ nsCSSScanner::ParseAndAppendEscape(nsString& aOutput, PRBool aInString)
   if ((ch > 0) && (ch != '\n')) {
     aOutput.Append(ch);
   }
+
+  return PR_TRUE;
 }
 
 /**
@@ -1080,7 +1089,9 @@ PRBool
 nsCSSScanner::GatherIdent(PRInt32 aChar, nsString& aIdent)
 {
   if (aChar == CSS_ESCAPE) {
-    ParseAndAppendEscape(aIdent, PR_FALSE);
+    if (!ParseAndAppendEscape(aIdent, PR_FALSE)) {
+      return PR_FALSE;
+    }
   }
   else if (0 < aChar) {
     aIdent.Append(aChar);
@@ -1107,7 +1118,10 @@ nsCSSScanner::GatherIdent(PRInt32 aChar, nsString& aIdent)
     aChar = Read();
     if (aChar < 0) break;
     if (aChar == CSS_ESCAPE) {
-      ParseAndAppendEscape(aIdent, PR_FALSE);
+      if (!ParseAndAppendEscape(aIdent, PR_FALSE)) {
+        Pushback(aChar);
+        break;
+      }
     } else if (IsIdent(aChar)) {
       aIdent.Append(PRUnichar(aChar));
     } else {
@@ -1381,7 +1395,21 @@ nsCSSScanner::ParseString(PRInt32 aStop, nsCSSToken& aToken)
       break;
     }
     if (ch == CSS_ESCAPE) {
-      ParseAndAppendEscape(aToken.mIdent, PR_TRUE);
+      if (!ParseAndAppendEscape(aToken.mIdent, PR_TRUE)) {
+        aToken.mType = eCSSToken_Bad_String;
+        Pushback(ch);
+#ifdef CSS_REPORT_PARSE_ERRORS
+        // For strings, the only case where ParseAndAppendEscape will
+        // return false is when there's a backslash to start an escape
+        // immediately followed by end-of-stream.  In that case, the
+        // correct tokenization is badstring *followed* by a DELIM for
+        // the backslash, but as far as the author is concerned, it
+        // works pretty much the same as an unterminated string, so we
+        // use the same error message.
+        ReportUnexpectedToken(aToken, "SEUnterminatedString");
+#endif
+        break;
+      }
     } else {
       aToken.mIdent.Append(ch);
     }

layout/style/nsCSSScanner.h

@@ -214,8 +214,8 @@ protected:
   PRBool LookAhead(PRUnichar aChar);
   PRBool LookAheadOrEOF(PRUnichar aChar); // expect either aChar or EOF
   void EatWhiteSpace();
-  
-  void ParseAndAppendEscape(nsString& aOutput, PRBool aInString);
+
+  PRBool ParseAndAppendEscape(nsString& aOutput, PRBool aInString);
   PRBool ParseIdent(PRInt32 aChar, nsCSSToken& aResult);
   PRBool ParseAtKeyword(PRInt32 aChar, nsCSSToken& aResult);
   PRBool ParseNumber(PRInt32 aChar, nsCSSToken& aResult);

layout/style/test/test_selectors.html

@@ -915,6 +915,9 @@ function run() {
     test_balanced_unparseable("p #, p");
     test_balanced_unparseable("p # , p");
 
+    // Test that a backslash alone is not treated as an escape.
+    test_unparseable_via_api("#\\");
+
     run_deferred_tests();
 }