fix(html): support comment on top (#4141)

src/language-html/parser-parse5.js

@@ -4,7 +4,7 @@ function parse(text /*, parsers, opts*/) {
   // Inline the require to avoid loading all the JS if we don't use it
   const parse5 = require("parse5");
   try {
-    const isFragment = !/^\s*<(!doctype|html|head|body)/i.test(text);
+    const isFragment = !/^\s*<(!doctype|html|head|body|!--)/i.test(text);
     const ast = (isFragment ? parse5.parseFragment : parse5.parse)(text, {
       treeAdapter: parse5.treeAdapters.htmlparser2,
       locationInfo: true

tests/html_basics/__snapshots__/jsfmt.spec.js.snap

@@ -42,6 +42,33 @@ exports[`hello-world.html 1`] = `
 </html>
 `;
 
+exports[`html-comments.html 1`] = `
+<!-- htmlhint attr-lowercase: false -->
+<html>
+  <body>
+    <a href="#">Anchor</a>
+    <div hidden class="foo" id=bar></div>
+  </body>
+</html>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+<!-- htmlhint attr-lowercase: false -->
+
+<html>
+
+<head />
+
+
+<body>
+  <a href="#">Anchor</a>
+  <div hidden
+    class="foo"
+    id="bar" />
+
+</body>
+</html>
+`;
+
 exports[`html-fragment.html 1`] = `
 <a href="#">Link</a>
 

tests/html_basics/html-comments.html

@@ -0,0 +1,7 @@
+<!-- htmlhint attr-lowercase: false -->
+<html>
+  <body>
+    <a href="#">Anchor</a>
+    <div hidden class="foo" id=bar></div>
+  </body>
+</html>