Don't emit an error on the ? ending an XML declaration

Fixes #2298

Author: jhy

CHANGES.md

@@ -23,6 +23,8 @@
   gets a declaration of `xmlns:prefix="undefined"`. This allows subsequent serializations to XML via `W3CDom.asString()`
   to succeed. [#2087](https://github.com/jhy/jsoup/issues/2087).
 * The `StreamParser` could emit the final elements of a document twice, due to how `onNodeCompleted` was fired when closing out the stack. [#2295](https://github.com/jhy/jsoup/issues/2295).
+* When parsing with the XML parser and error tracking enabled, the trailing `?` in `<?xml version="1.0"?>` would
+  incorrectly emit an error. [#2298](https://github.com/jhy/jsoup/issues/2298).
 
 ## 1.19.1 (2025-03-04)
 

src/main/java/org/jsoup/parser/TokeniserState.java

@@ -1,6 +1,7 @@
 package org.jsoup.parser;
 
 import org.jsoup.nodes.DocumentType;
+import org.jsoup.nodes.XmlDeclaration;
 
 import static org.jsoup.nodes.Document.OutputSettings.Syntax.xml;
 
@@ -891,6 +892,10 @@ private void anythingElse(Tokeniser t, CharacterReader r) {
                     t.eofError(this);
                     t.transition(Data);
                     break;
+                case '?': // Handle trailing ? in <?xml...?>
+                    if (t.tagPending instanceof Token.XmlDecl)
+                        break;
+                    // otherwise fall through to default
                 default:
                     r.unconsume();
                     t.error(this);

src/test/java/org/jsoup/parser/XmlTreeBuilderTest.java

@@ -394,4 +394,19 @@ private static void assertXmlNamespace(Element el) {
         assertEquals("<val2>", decl.attr("att2"));
     }
 
+    @Test void xmlHeaderIsValid() {
+        // https://github.com/jhy/jsoup/issues/2298
+        String xml = "<?xml version=\"1.0\"?>\n<root></root>";
+        String expect = xml;
+
+        Document doc = Jsoup.parse(xml, Parser.xmlParser().setTrackErrors(10));
+        assertEquals(0, doc.parser().getErrors().size());
+        assertEquals(expect, doc.html());
+
+        xml =  "<?xml version=\"1.0\" ?>\n<root></root>";
+        doc = Jsoup.parse(xml, Parser.xmlParser().setTrackErrors(10));
+        assertEquals(0, doc.parser().getErrors().size());
+        assertEquals(expect, doc.html());
+    }
+
 }