Fix head opening tag omission w/o title

While typically a `title` is needed, there are cases where `<head>` can be empty, in which case, the start tag can be omitted. Closes GH-43.
syntax-tree · Sep 16, 2024 · 1c938b9 · 1c938b9
1 parent a556b7d
commit 1c938b9
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Showing 3 changed files with 22 additions and 17 deletions.
diff --git a/lib/omission/opening.js b/lib/omission/opening.js
@@ -37,23 +37,25 @@ function html(node) {
  *   Whether the opening tag can be omitted.
  */
 function head(node) {
-  const children = node.children
-  /** @type {Array<string>} */
-  const seen = []
-  let index = -1
+  /** @type {Set<string>} */
+  const seen = new Set()
 
-  while (++index < children.length) {
-    const child = children[index]
+  // Whether `srcdoc` or not,
+  // make sure the content model at least doesn’t have too many `base`s/`title`s.
+  for (const child of node.children) {
     if (
       child.type === 'element' &&
-      (child.tagName === 'title' || child.tagName === 'base')
+      (child.tagName === 'base' || child.tagName === 'title')
     ) {
-      if (seen.includes(child.tagName)) return false
-      seen.push(child.tagName)
+      if (seen.has(child.tagName)) return false
+      seen.add(child.tagName)
     }
   }
 
-  return children.length > 0
+  // “May be omitted if the element is empty,
+  // or if the first thing inside the head element is an element.”
+  const child = node.children[0]
+  return !child || child.type === 'element'
 }
 
 /**

diff --git a/test/omission-closing-head.js b/test/omission-closing-head.js
@@ -6,7 +6,7 @@ import {u} from 'unist-builder'
 
 test('`head` (closing)', async function (t) {
   await t.test('should omit tag without following', async function () {
-    assert.deepEqual(toHtml(h('head'), {omitOptionalTags: true}), '<head>')
+    assert.deepEqual(toHtml(h('head'), {omitOptionalTags: true}), '')
   })
 
   await t.test(
@@ -16,7 +16,7 @@ test('`head` (closing)', async function (t) {
         toHtml(h('html', [h('head'), u('comment', 'alpha')]), {
           omitOptionalTags: true
         }),
-        '<head></head><!--alpha-->'
+        '</head><!--alpha-->'
       )
     }
   )
@@ -26,7 +26,7 @@ test('`head` (closing)', async function (t) {
     async function () {
       assert.deepEqual(
         toHtml(h('html', [h('head'), ' alpha']), {omitOptionalTags: true}),
-        '<head></head> alpha'
+        '</head> alpha'
       )
     }
   )
@@ -38,7 +38,7 @@ test('`head` (closing)', async function (t) {
         toHtml(h('html', [h('head'), u('text', 'alpha')]), {
           omitOptionalTags: true
         }),
-        '<head>alpha'
+        'alpha'
       )
     }
   )

diff --git a/test/omission-opening-head.js b/test/omission-opening-head.js
@@ -11,9 +11,12 @@ test('`head` (opening)', async function (t) {
     )
   })
 
-  await t.test('should not omit tag without children', async function () {
-    assert.deepEqual(toHtml(h('head'), {omitOptionalTags: true}), '<head>')
-  })
+  await t.test(
+    'should omit tag without children (could be fine in `srcdoc`)',
+    async function () {
+      assert.deepEqual(toHtml(h('head'), {omitOptionalTags: true}), '')
+    }
+  )
 
   await t.test('should omit tag with `title`', async function () {
     assert.deepEqual(