Add InputClosesSelect flag

This flag is intended to de-risk the launch of SelectParserRelaxation by
partially reverting the new parser behavior to the old parser behavior
specifically in the case of an <input> tag being parsed inside a
<select>. The old parser would convert <select><input> into
<select></select><input>, and based on my research, this is the case
that is most likely going to break sites in SelectParserRelaxation:
whatwg/html#10310

Bug: 373672164
Change-Id: I33b40d11c2001092aa076a219dd56c5ea86f13f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5936092
Reviewed-by: Mason Freed <[email protected]>
Commit-Queue: Joey Arhar <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1369676}

Author: josepharhar

third_party/blink/renderer/core/html/parser/html_tree_builder.cc

@@ -748,6 +748,11 @@ void HTMLTreeBuilder::ProcessStartTagForInBody(AtomicHTMLToken* token) {
       ProcessCloseWhenNestedTag<IsLi>(token);
       break;
     case HTMLTag::kInput: {
+      if (RuntimeEnabledFeatures::InputClosesSelectEnabled()) {
+        if (tree_.OpenElements()->InScope(HTMLTag::kSelect)) {
+          ProcessFakeEndTag(HTMLTag::kSelect);
+        }
+      }
       // Per spec https://html.spec.whatwg.org/C/#parsing-main-inbody,
       // section "A start tag whose tag name is "input""
 

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -2409,6 +2409,14 @@
       name: "InnerHTMLParserFastpathLogFailure",
       status: "experimental",
     },
+    {
+      // Makes the HTML parser close <select> tags before inserting <input>
+      // tags to match the old parser behavior in case we have compat issues
+      // launching SelectParserRelaxation. If SelectParserRelaxation stays
+      // stable in M131, then this flag can be removed in M133.
+      name: "InputClosesSelect",
+      depends_on: ["SelectParserRelaxation"],
+    },
     {
       name: "InputMultipleFieldsUI",
       // No plan to support complex UI for date/time INPUT types on Android and

third_party/blink/web_tests/VirtualTestSuites

@@ -3497,6 +3497,16 @@
     "expires": "Feb 1, 2025",
     "owners": ["[email protected]", "[email protected]"]
   },
+  {
+    "prefix": "input-closes-select",
+    "platforms": ["Linux"],
+    "bases": [
+      "external/wpt/html/semantics/forms/the-select-element/customizable-select/select-parsing.tentative.html"
+    ],
+    "args": ["--enable-features=InputClosesSelect,SelectParserRelaxation"],
+    "expires": "Feb 1, 2025",
+    "owners": ["[email protected]", "[email protected]"]
+  },
   "css-custom-state-deprecated-syntax-enabled is the configuration that is",
   "currently shipping to stable.",
   {

third_party/blink/web_tests/external/wpt/html/semantics/forms/the-select-element/customizable-select/select-parsing.tentative.html

@@ -42,6 +42,10 @@
   </div>
 </select>
 
+<select id=s7>
+  <input>
+</select>
+
 <div id=afterlast>
   keep this div after the last test case
 </div>
@@ -100,6 +104,13 @@
 `);
 }, 'Divs and imgs should be allowed as direct children of select and within options without a datalist.');
 
+test(() => {
+  assert_equals(document.getElementById('s7').parentNode, document.body);
+  assert_equals(document.getElementById('s7').innerHTML, `
+  <input>
+`);
+}, 'Input tags should parse inside select instead of closing the select.');
+
 test(() => {
   assert_equals(document.getElementById('afterlast').parentNode, document.body);
 }, 'The last test should not leave any tags open after parsing.');

third_party/blink/web_tests/virtual/customizable-select-disabled/external/wpt/html/semantics/forms/the-select-element/customizable-select/select-parsing.tentative-expected.txt

@@ -11,5 +11,7 @@ This is a testharness.js-based test.
   assert_equals: expected "\\n  <button>\\n    <div>\\n      </div></button>" but got "\\n  \\n    \\n      "
 [FAIL] Divs and imgs should be allowed as direct children of select and within options without a datalist.
   assert_equals: expected "\\n  <div>\\n    <option><img>option</option>\\n  </div>\\n" but got "\\n  \\n    <option>option</option>\\n  \\n"
+[FAIL] Input tags should parse inside select instead of closing the select.
+  assert_equals: expected "\\n  <input>\\n" but got "\\n  "
 Harness: the test ran to completion.
 

third_party/blink/web_tests/virtual/input-closes-select/README.md

@@ -0,0 +1,5 @@
+This suite enables InputClosesSelect flag, which re-adds legacy behavior to the
+HTML parser which turns `<select><input>` into `<select></select><input>` to
+de-risk the launch of SelectParserRelaxation.
+
+--enable-features=SelectParserRelaxation,InputClosesSelect

third_party/blink/web_tests/virtual/input-closes-select/external/wpt/html/semantics/forms/the-select-element/customizable-select/select-parsing.tentative-expected.txt

@@ -0,0 +1,5 @@
+This is a testharness.js-based test.
+[FAIL] Input tags should parse inside select instead of closing the select.
+  assert_equals: expected "\\n  <input>\\n" but got "\\n  "
+Harness: the test ran to completion.
+