[fixes #3310] Ignore non-static/non-public extension methods

src/core/lombok/javac/handlers/HandleExtensionMethod.java

@@ -117,7 +117,8 @@ public class HandleExtensionMethod extends JavacAnnotationHandler<ExtensionMetho
 		if (tsym != null) for (Symbol member : tsym.getEnclosedElements()) {
 			if (member.getKind() != ElementKind.METHOD) continue;
 			MethodSymbol method = (MethodSymbol) member;
-			if ((method.flags() & (STATIC | PUBLIC)) == 0) continue;
+			if ((method.flags() & STATIC) == 0) continue;
+			if ((method.flags() & PUBLIC) == 0) continue;
 			if (method.params().isEmpty()) continue;
 			extensionMethods.add(method);
 		}

test/transform/resource/after-delombok/ExtensionMethodNonStatic.java

@@ -0,0 +1,12 @@
+class ExtensionMethodNonStatic {
+	public void test() {
+		String s = "test";
+		s.startsWith("");
+	}
+
+	static class Extensions {
+		public boolean startsWith(String s, String prefix) {
+			return s.startsWith(prefix);
+		}
+	}
+}

test/transform/resource/after-ecj/ExtensionMethodNonStatic.java

@@ -0,0 +1,18 @@
+import lombok.experimental.ExtensionMethod;
+@ExtensionMethod({ExtensionMethodNonStatic.Extensions.class}) class ExtensionMethodNonStatic {
+  static class Extensions {
+    Extensions() {
+      super();
+    }
+    public boolean startsWith(String s, String prefix) {
+      return s.startsWith(prefix);
+    }
+  }
+  ExtensionMethodNonStatic() {
+    super();
+  }
+  public void test() {
+    String s = "test";
+    s.startsWith("");
+  }
+}

test/transform/resource/before/ExtensionMethodNonStatic.java

@@ -0,0 +1,15 @@
+import lombok.experimental.ExtensionMethod;
+
+@ExtensionMethod({ExtensionMethodNonStatic.Extensions.class})
+class ExtensionMethodNonStatic {
+	public void test() {
+		String s = "test";
+		s.startsWith("");
+	}
+
+	static class Extensions {
+		public boolean startsWith(String s, String prefix) {
+			return s.startsWith(prefix);
+		}
+	}
+}