Fix: Convert By.className to css selector for Firefox inside Shadow DOM

Author: nityanandbb

java/src/org/openqa/selenium/remote/ShadowRoot.java

@@ -31,6 +31,7 @@
 import org.openqa.selenium.WebElement;
 import org.openqa.selenium.WrapsDriver;
 import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.remote.shadow.FirefoxClassNameWorkaround;
 
 // Note: we want people to code against the SearchContext API, so we keep this class package private
 class ShadowRoot implements SearchContext, WrapsDriver {
@@ -44,18 +45,20 @@ class ShadowRoot implements SearchContext, WrapsDriver {
 
   @Override
   public List<WebElement> findElements(By by) {
+    By resolved = FirefoxClassNameWorkaround.resolveForShadow(by, this);
     return parent.findElements(
         this,
         (using, value) -> FIND_ELEMENTS_FROM_SHADOW_ROOT(id, using, String.valueOf(value)),
-        by);
+        resolved);
   }
 
   @Override
   public WebElement findElement(By by) {
+    By resolved = FirefoxClassNameWorkaround.resolveForShadow(by, this);
     return parent.findElement(
         this,
         (using, value) -> FIND_ELEMENT_FROM_SHADOW_ROOT(id, using, String.valueOf(value)),
-        by);
+        resolved);
   }
 
   @Override
@@ -73,12 +76,8 @@ private Map<String, Object> toJson() {
 
   @Override
   public boolean equals(Object o) {
-    if (this == o) {
-      return true;
-    }
-    if (o == null || getClass() != o.getClass()) {
-      return false;
-    }
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
     ShadowRoot that = (ShadowRoot) o;
     return Objects.equals(parent, that.parent) && Objects.equals(id, that.id);
   }

java/src/org/openqa/selenium/remote/shadow/FirefoxClassNameWorkaround.java

@@ -0,0 +1,44 @@
+package org.openqa.selenium.remote.shadow;
+
+import org.openqa.selenium.By;
+import org.openqa.selenium.InvalidSelectorException;
+import org.openqa.selenium.SearchContext;
+import org.openqa.selenium.WebDriver;
+import org.openqa.selenium.WrapsDriver;
+import org.openqa.selenium.remote.HasCapabilities;
+import org.openqa.selenium.Capabilities;
+
+final class FirefoxClassNameWorkaround {
+
+    static boolean shouldUseCssSelector(By by, SearchContext context) {
+        if (!(by instanceof By.ByClassName)) return false;
+        if (!(context instanceof WrapsDriver)) return false;
+
+        try {
+            WebDriver driver = ((WrapsDriver) context).getWrappedDriver();
+            Capabilities caps = ((HasCapabilities) driver).getCapabilities();
+            return "firefox".equalsIgnoreCase(caps.getBrowserName());
+        } catch (Exception ignored) {
+            return false;
+        }
+    }
+
+    static By convertToCss(By by) {
+        String className = extractClassName(by);
+        if (className.contains(" ")) {
+            throw new InvalidSelectorException(
+                "Compound class names not supported in Firefox Shadow DOM. Use single class name or By.cssSelector instead."
+            );
+        }
+        return By.cssSelector("." + className);
+    }
+
+    private static String extractClassName(By by) {
+        String raw = by.toString().replace("By.className:", "").trim();
+        return raw.replaceAll("\\s+", "");
+    }
+
+    public static By resolveForShadow(By by, SearchContext context) {
+        return shouldUseCssSelector(by, context) ? convertToCss(by) : by;
+    }
+}