Initialize startPos to 0 vs -1

So that nodes that are added without first going through transition() have the correct start pos.

Fixes #2106

CHANGES.md

@@ -13,6 +13,11 @@
 
 * Removed previously deprecated internal classes and methods. [2094](https://github.com/jhy/jsoup/pull/2094)
 
+### Bug Fixes
+
+* When tracking source positions, if the first node was a TextNode, its position was incorrectly set
+  to `-1.` [2106](https://github.com/jhy/jsoup/issues/2106)
+
 ---
 
 ## 1.17.2 (2023-Dec-29)

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

@@ -50,7 +50,7 @@ final class Tokeniser {
     @Nullable private String lastStartCloseSeq; // "</" + lastStartTag, so we can quickly check for that in RCData
 
     private static final int Unset = -1;
-    private int markupStartPos, charStartPos = Unset; // reader pos at the start of markup / characters. updated on state transition
+    private int markupStartPos, charStartPos = 0; // reader pos at the start of markup / characters. updated on state transition. Initialized to start (0), but set to Unset after emissions.
 
     Tokeniser(TreeBuilder treeBuilder) {
         tagPending = startPending  = new Token.StartTag(treeBuilder);

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

@@ -487,6 +487,15 @@ private void printRange(Node node) {
         assertEquals("h1:0-9~12-17; id:4-6=7-8; #text:9-12; #text:17-18; h2:18-27~30-35; id:22-24=25-26; #text:27-30; h10:35-40~43-49; #text:40-43; ", track.toString());
     }
 
+    @Test void tracksFirstTextnode() {
+        // https://github.com/jhy/jsoup/issues/2106
+        String html = "foo<p></p>bar<p></p><div><b>baz</b></div>";
+        Document doc = Jsoup.parse(html, TrackingHtmlParser);
+        StringBuilder track = new StringBuilder();
+        doc.body().forEachNode(node -> accumulatePositions(node, track));
+        assertEquals("body:0-0~41-41; #text:0-3; p:3-6~6-10; #text:10-13; p:13-16~16-20; div:20-25~35-41; b:25-28~31-35; #text:28-31; ", track.toString());
+    }
+
     @Test void updateKeyMaintainsRangeLc() {
         String html = "<p xsi:CLASS=On>One</p>";
         Document doc = Jsoup.parse(html, TrackingHtmlParser);