fix: add td to th's implicit close set (#2389)

Opening a <th> now correctly auto-closes an open <td>, matching the
HTML spec's optional tag rules. Previously <th> only closed other <th>
elements, which caused <th> to become a child of <td> instead of a
sibling. The <td> entry already had this the other way around.

Ref: https://html.spec.whatwg.org/multipage/syntax.html#optional-tags

Author: vimzh

src/Parser.spec.ts

@@ -179,6 +179,25 @@ describe("API", () => {
         p.write("<__proto__>");
     });
 
+    it("should implicitly close <td> when <th> opens", () => {
+        const onclosetag = vi.fn();
+        const onopentagname = vi.fn();
+
+        new Parser({ onclosetag, onopentagname }).end(
+            "<table><tr><td>A<th>B</tr></table>",
+        );
+
+        // <th> must auto-close <td>, making them siblings per the HTML spec
+        expect(onclosetag).toHaveBeenCalledWith("td", true);
+        const tdClose = onclosetag.mock.calls.findIndex(
+            ([name]: [string]) => name === "td",
+        );
+        const thOpen = onopentagname.mock.calls.findIndex(
+            ([name]: [string]) => name === "th",
+        );
+        expect(tdClose).toBeLessThan(thOpen);
+    });
+
     it("should support custom tokenizer", () => {
         class CustomTokenizer extends Tokenizer {}
 

src/Parser.ts

@@ -19,7 +19,7 @@ const rtpTags = new Set(["rt", "rp"]);
 
 const openImpliesClose = new Map<string, Set<string>>([
     ["tr", new Set(["tr", "th", "td"])],
-    ["th", new Set(["th"])],
+    ["th", new Set(["th", "td"])],
     ["td", new Set(["thead", "th", "td"])],
     ["body", new Set(["head", "link", "script"])],
     ["a", new Set(["a"])],