From 1b63adfba840d50cc7c0f7ed409a9dbf2498c002 Mon Sep 17 00:00:00 2001
From: Ronald Brill <rbri@rbri.de>
Date: Sat, 15 Apr 2023 13:42:13 +0200
Subject: [PATCH] try different ways of doing lookahead

---
 src/main/javacc/CSS3Parser.jj                 | 50 ++++++++++++++++++-
 .../cssparser/parser/CSS3ParserTest.java      | 33 ++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/src/main/javacc/CSS3Parser.jj b/src/main/javacc/CSS3Parser.jj
index 7995c10..e99f368 100644
--- a/src/main/javacc/CSS3Parser.jj
+++ b/src/main/javacc/CSS3Parser.jj
@@ -1108,7 +1108,11 @@ Selector selector() :
 {
     try {
         sel = simpleSelector(null, ' ')
-        ( LOOKAHEAD(2) comb = combinator() sel = simpleSelector(sel, comb) )* ( <S> )*
+        (
+          LOOKAHEAD(2)
+          /* LOOKAHEAD(combinator() ( <IDENT> | <ASTERISK> | <HASH> | <DOT> | <LSQUARE> | <COLON> )) */
+          /* LOOKAHEAD( { isCombinator() }) */
+          comb = combinator() sel = simpleSelector(sel, comb) )* ( <S> )*
         {
             return sel;
         }
@@ -2429,3 +2433,47 @@ Boolean handleCaseInSensitive(Token t)
 
     throw toCSSParseException("invalidCaseInSensitivelyIdentifier", new String[] { s }, createLocator(t));
 }
+
+JAVACODE
+boolean isCombinator()
+{
+  Token token = getToken(1);
+  if (token.kind == EOF) { return false; }
+
+  if (token.kind == S) {
+    token = getToken(2);
+    if (token.kind == EOF) { return false; }
+
+    if (token.kind == PLUS || token.kind == GREATER || token.kind == TILDE) {
+      token = getToken(3);
+      if (token.kind == EOF) { return false; }
+      if (token.kind == S) {
+        token = getToken(4);
+        if (token.kind == EOF) { return false; }
+      }
+    }
+
+    return token.kind == IDENT
+            || token.kind == ASTERISK
+            || token.kind == HASH
+            || token.kind == DOT
+            || token.kind == LSQUARE
+            || token.kind == COLON;
+  }
+  else if (token.kind == PLUS || token.kind == GREATER || token.kind == TILDE) {
+    token = getToken(2);
+    if (token.kind == EOF) { return false; }
+    if (token.kind == S) {
+      token = getToken(3);
+      if (token.kind == EOF) { return false; }
+    }
+
+    return token.kind == IDENT
+            || token.kind == ASTERISK
+            || token.kind == HASH
+            || token.kind == DOT
+            || token.kind == LSQUARE
+            || token.kind == COLON;
+  }
+  return false;
+}
diff --git a/src/test/java/org/htmlunit/cssparser/parser/CSS3ParserTest.java b/src/test/java/org/htmlunit/cssparser/parser/CSS3ParserTest.java
index d22429a..6a0cc06 100644
--- a/src/test/java/org/htmlunit/cssparser/parser/CSS3ParserTest.java
+++ b/src/test/java/org/htmlunit/cssparser/parser/CSS3ParserTest.java
@@ -4498,6 +4498,39 @@ public void doubleColonsPseudoClass() throws Exception {
         assertEquals("h1::link { color: red; }", rule.getCssText());
     }
 
+    /**
+     * @throws Exception if the test fails
+     */
+    @Test
+    public void performance() throws Exception {
+        for (int i = 0; i < 40; i++) {
+            realWorld("realworld/style.csx.css");
+            realWorld("realworld/compass-homestyle.css");
+            realWorld("realworld/www.css");
+            realWorld("realworld/home.built.css");
+            realWorld("realworld/load.php.css");
+            realWorld("realworld/normalize.css");
+            realWorld("realworld/cargo.css");
+            realWorld("realworld/blueprint/screen.css");
+            realWorld("realworld/blueprint/print.css");
+            realWorld("realworld/blueprint/ie.css");
+            realWorld("realworld/bootstrap_3_3_7_min.css");
+            realWorld("realworld/bootstrap_4_0_0.css");
+            realWorld("realworld/bootstrap_4_0_0_min.css");
+            realWorld("realworld/style-V5-11.css");
+            realWorld("realworld/all.css");
+        }
+    }
+
+    private static final CSSOMParser p = new CSSOMParser();
+
+    private void realWorld(final String resourceName) throws Exception {
+        final InputStream is = getClass().getClassLoader().getResourceAsStream(resourceName);
+        assertNotNull(is);
+
+        final InputSource css = new InputSource(new InputStreamReader(is, StandardCharsets.UTF_8));
+        p.parseStyleSheet(css, null);
+    }
 //
 //    /**
 //     * @throws Exception if any error occurs