From 40270cb6269f3f2d054bcfe51c69c8c545447f9a Mon Sep 17 00:00:00 2001
From: Kenzie Raditya Tirtarahardja <kenzieradityatirtarahardja18@gmail.com>
Date: Sun, 23 Mar 2025 08:45:59 +0800
Subject: [PATCH] Make input element display-inside always flow-root (#35908)

Signed-off-by: Kenzie Raditya Tirtarahardja <kenzieradityatirtarahardja.18@gmail.com>
Co-authored-by: Kenzie Raditya Tirtarahardja <kenzieradityatirtarahardja.18@gmail.com>
---
 components/layout_2020/dom_traversal.rs       | 30 +++++++++++++++++--
 .../fragment_tree/base_fragment.rs            | 16 +++++-----
 .../layout_2020/fragment_tree/box_fragment.rs |  4 +--
 components/layout_2020/style_ext.rs           | 28 +++++++++++++++--
 tests/wpt/meta/MANIFEST.json                  | 24 +++++++++++++++
 .../widgets/text-control-client-width.html    | 19 ++++++++++++
 .../widgets/text-control-flow-root-ref.html   | 14 +++++++++
 .../widgets/text-control-flow-root.html       | 17 +++++++++++
 8 files changed, 136 insertions(+), 16 deletions(-)
 create mode 100644 tests/wpt/tests/html/rendering/widgets/text-control-client-width.html
 create mode 100644 tests/wpt/tests/html/rendering/widgets/text-control-flow-root-ref.html
 create mode 100644 tests/wpt/tests/html/rendering/widgets/text-control-flow-root.html

diff --git a/components/layout_2020/dom_traversal.rs b/components/layout_2020/dom_traversal.rs
index 6b44c7f46b4..b8a39ad27fe 100644
--- a/components/layout_2020/dom_traversal.rs
+++ b/components/layout_2020/dom_traversal.rs
@@ -116,6 +116,15 @@ where
                 },
                 _ => {},
             }
+
+            if matches!(
+                element.type_id(),
+                Some(LayoutNodeType::Element(
+                    LayoutElementType::HTMLInputElement | LayoutElementType::HTMLTextAreaElement
+                ))
+            ) {
+                flags.insert(FragmentFlags::IS_TEXT_CONTROL);
+            }
         };
 
         Self {
@@ -135,12 +144,15 @@ pub(super) enum Contents {
 }
 
 #[derive(Debug)]
+#[allow(clippy::enum_variant_names)]
 pub(super) enum NonReplacedContents {
     /// Refers to a DOM subtree, plus `::before` and `::after` pseudo-elements.
     OfElement,
     /// Content of a `::before` or `::after` pseudo-element that is being generated.
     /// <https://drafts.csswg.org/css2/generate.html#content>
     OfPseudoElement(Vec<PseudoElementContentItem>),
+    /// Workaround for input and textarea element until we properly implement `display-inside`.
+    OfTextControl,
 }
 
 #[derive(Debug)]
@@ -236,8 +248,18 @@ fn traverse_element<'dom, Node>(
             }
         },
         Display::GeneratingBox(display) => {
-            let contents =
-                replaced.map_or(NonReplacedContents::OfElement.into(), Contents::Replaced);
+            let contents = if let Some(replaced) = replaced {
+                Contents::Replaced(replaced)
+            } else if matches!(
+                element.type_id(),
+                LayoutNodeType::Element(
+                    LayoutElementType::HTMLInputElement | LayoutElementType::HTMLTextAreaElement
+                )
+            ) {
+                NonReplacedContents::OfTextControl.into()
+            } else {
+                NonReplacedContents::OfElement.into()
+            };
             let display = display.used_value_for_contents(&contents);
             let box_slot = element.element_box_slot();
             let info = NodeAndStyleInfo::new(element, style);
@@ -366,7 +388,9 @@ impl NonReplacedContents {
             },
         };
         match self {
-            NonReplacedContents::OfElement => traverse_children_of(node, context, handler),
+            NonReplacedContents::OfElement | NonReplacedContents::OfTextControl => {
+                traverse_children_of(node, context, handler)
+            },
             NonReplacedContents::OfPseudoElement(items) => {
                 traverse_pseudo_element_contents(info, context, handler, items)
             },
diff --git a/components/layout_2020/fragment_tree/base_fragment.rs b/components/layout_2020/fragment_tree/base_fragment.rs
index 38f4f6ba815..45d10d5e282 100644
--- a/components/layout_2020/fragment_tree/base_fragment.rs
+++ b/components/layout_2020/fragment_tree/base_fragment.rs
@@ -75,31 +75,33 @@ impl From<BaseFragmentInfo> for BaseFragment {
 bitflags! {
     /// Flags used to track various information about a DOM node during layout.
     #[derive(Clone, Copy, Debug)]
-    pub(crate) struct FragmentFlags: u8 {
+    pub(crate) struct FragmentFlags: u16 {
         /// Whether or not the node that created this fragment is a `<body>` element on an HTML document.
         const IS_BODY_ELEMENT_OF_HTML_ELEMENT_ROOT = 1 << 0;
         /// Whether or not the node that created this Fragment is a `<br>` element.
         const IS_BR_ELEMENT = 1 << 1;
+        /// Whether or not the node that created this Fragment is a `<input>` or `<textarea>` element.
+        const IS_TEXT_CONTROL = 1 << 2;
         /// Whether or not this Fragment is a flex item or a grid item.
-        const IS_FLEX_OR_GRID_ITEM = 1 << 2;
+        const IS_FLEX_OR_GRID_ITEM = 1 << 3;
         /// Whether or not this Fragment was created to contain a replaced element or is
         /// a replaced element.
-        const IS_REPLACED = 1 << 3;
+        const IS_REPLACED = 1 << 4;
         /// Whether or not the node that created was a `<table>`, `<th>` or
         /// `<td>` element. Note that this does *not* include elements with
         /// `display: table` or `display: table-cell`.
-        const IS_TABLE_TH_OR_TD_ELEMENT = 1 << 4;
+        const IS_TABLE_TH_OR_TD_ELEMENT = 1 << 5;
         /// Whether or not this Fragment was created to contain a list item marker
         /// with a used value of `list-style-position: outside`.
-        const IS_OUTSIDE_LIST_ITEM_MARKER = 1 << 5;
+        const IS_OUTSIDE_LIST_ITEM_MARKER = 1 << 6;
         /// Avoid painting the borders, backgrounds, and drop shadow for this fragment, this is used
         /// for empty table cells when 'empty-cells' is 'hide' and also table wrappers.  This flag
         /// doesn't avoid hit-testing nor does it prevent the painting outlines.
-        const DO_NOT_PAINT = 1 << 6;
+        const DO_NOT_PAINT = 1 << 7;
         /// Whether or not the size of this fragment depends on the block size of its container
         /// and the fragment can be a flex item. This flag is used to cache items during flex
         /// layout.
-        const SIZE_DEPENDS_ON_BLOCK_CONSTRAINTS_AND_CAN_BE_CHILD_OF_FLEX_ITEM = 1 << 7;
+        const SIZE_DEPENDS_ON_BLOCK_CONSTRAINTS_AND_CAN_BE_CHILD_OF_FLEX_ITEM = 1 << 8;
     }
 }
 
diff --git a/components/layout_2020/fragment_tree/box_fragment.rs b/components/layout_2020/fragment_tree/box_fragment.rs
index 1c8862b0822..f8f0e233a2f 100644
--- a/components/layout_2020/fragment_tree/box_fragment.rs
+++ b/components/layout_2020/fragment_tree/box_fragment.rs
@@ -15,7 +15,6 @@ use style::properties::ComputedValues;
 
 use super::{BaseFragment, BaseFragmentInfo, CollapsedBlockMargins, Fragment};
 use crate::formatting_contexts::Baselines;
-use crate::fragment_tree::FragmentFlags;
 use crate::geom::{
     AuOrAuto, LengthPercentageOrAuto, PhysicalPoint, PhysicalRect, PhysicalSides, ToLogical,
 };
@@ -346,8 +345,7 @@ impl BoxFragment {
     /// Whether this is a non-replaced inline-level box whose inner display type is `flow`.
     /// <https://drafts.csswg.org/css-display-3/#inline-box>
     pub(crate) fn is_inline_box(&self) -> bool {
-        self.style.get_box().display.is_inline_flow() &&
-            !self.base.flags.contains(FragmentFlags::IS_REPLACED)
+        self.style.is_inline_box(self.base.flags)
     }
 
     /// Whether this is a table wrapper box.
diff --git a/components/layout_2020/style_ext.rs b/components/layout_2020/style_ext.rs
index 92c7b1f3314..57207186f81 100644
--- a/components/layout_2020/style_ext.rs
+++ b/components/layout_2020/style_ext.rs
@@ -30,7 +30,7 @@ use style::values::specified::{Overflow, WillChangeBits, box_ as stylo};
 use webrender_api as wr;
 use webrender_api::units::LayoutTransform;
 
-use crate::dom_traversal::Contents;
+use crate::dom_traversal::{Contents, NonReplacedContents};
 use crate::fragment_tree::FragmentFlags;
 use crate::geom::{
     AuOrAuto, LengthPercentageOrAuto, LogicalSides, LogicalSides1D, LogicalVec2, PhysicalSides,
@@ -83,6 +83,22 @@ impl DisplayGeneratingBox {
                     is_list_item: false,
                 },
             }
+        } else if matches!(
+            contents,
+            Contents::NonReplaced(NonReplacedContents::OfTextControl)
+        ) {
+            // If it's an input or textarea, make sure the display-inside is flow-root.
+            // <https://html.spec.whatwg.org/multipage/#form-controls>
+            if let DisplayGeneratingBox::OutsideInside { outside, .. } = self {
+                DisplayGeneratingBox::OutsideInside {
+                    outside: *outside,
+                    inside: DisplayInside::FlowRoot {
+                        is_list_item: false,
+                    },
+                }
+            } else {
+                *self
+            }
         } else {
             *self
         }
@@ -334,6 +350,7 @@ pub(crate) trait ComputedValuesExt {
         &self,
         writing_mode: WritingMode,
     ) -> bool;
+    fn is_inline_box(&self, fragment_flags: FragmentFlags) -> bool;
 }
 
 impl ComputedValuesExt for ComputedValues {
@@ -483,6 +500,12 @@ impl ComputedValuesExt for ComputedValues {
         LogicalSides::from_physical(&self.physical_margin(), containing_block_writing_mode)
     }
 
+    fn is_inline_box(&self, fragment_flags: FragmentFlags) -> bool {
+        self.get_box().display.is_inline_flow() &&
+            !fragment_flags
+                .intersects(FragmentFlags::IS_REPLACED | FragmentFlags::IS_TEXT_CONTROL)
+    }
+
     /// Returns true if this is a transformable element.
     fn is_transformable(&self, fragment_flags: FragmentFlags) -> bool {
         // "A transformable element is an element in one of these categories:
@@ -494,8 +517,7 @@ impl ComputedValuesExt for ComputedValues {
         //     elements."
         // <https://drafts.csswg.org/css-transforms/#transformable-element>
         // TODO: check for all cases listed in the above spec.
-        !self.get_box().display.is_inline_flow() ||
-            fragment_flags.contains(FragmentFlags::IS_REPLACED)
+        !self.is_inline_box(fragment_flags)
     }
 
     /// Returns true if this style has a transform, or perspective property set and
diff --git a/tests/wpt/meta/MANIFEST.json b/tests/wpt/meta/MANIFEST.json
index 642d038d314..117f1af832b 100644
--- a/tests/wpt/meta/MANIFEST.json
+++ b/tests/wpt/meta/MANIFEST.json
@@ -347578,6 +347578,19 @@
         {}
        ]
       ],
+      "text-control-flow-root.html": [
+       "54f7612da34262e9f804d5fcc6af0e71dafd3af8",
+       [
+        null,
+        [
+         [
+          "/html/rendering/widgets/text-control-flow-root-ref.html",
+          "=="
+         ]
+        ],
+        {}
+       ]
+      ],
       "the-select-element": {
        "option-add-label-quirks.html": [
         "2c3c8093e253250f11a7e84a7ba89f3535d2eb20",
@@ -473527,6 +473540,10 @@
        "938d2659a8a8c02230c92db5b575818a5d056809",
        []
       ],
+      "text-control-flow-root-ref.html": [
+       "df2783540d87462a6c0f99c7d2e6bf6e7fd657a1",
+       []
+      ],
       "the-select-element": {
        "option-checked-styling-ref.html": [
         "92504a47b5961a7fa64b98b9382327b7be8e3c83",
@@ -717904,6 +717921,13 @@
         {}
        ]
       ],
+      "text-control-client-width.html": [
+       "cfded6804dba6d5cc82472cae2cc276a7092741a",
+       [
+        null,
+        {}
+       ]
+      ],
       "textarea-cols-rows.html": [
        "5d02a4653ef77fbaab8b1c7aa8df933a8eabcd47",
        [
diff --git a/tests/wpt/tests/html/rendering/widgets/text-control-client-width.html b/tests/wpt/tests/html/rendering/widgets/text-control-client-width.html
new file mode 100644
index 00000000000..cfded6804db
--- /dev/null
+++ b/tests/wpt/tests/html/rendering/widgets/text-control-client-width.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>text control with `display: inline` must not have 0 client width</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/rendering.html#form-controls">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<input id="input" style="display: inline;">
+<textarea id="textarea" style="display: inline;"></textarea>
+
+<script>
+test(() => {
+  assert_greater_than(document.querySelector("#input").clientWidth, 0);
+}, "Input with `display: inline` should have positive client width");
+
+test(() => {
+  assert_greater_than(document.querySelector("#textarea").clientWidth, 0);
+}, "Textarea with `display: inline` should have positive client width");
+</script>
diff --git a/tests/wpt/tests/html/rendering/widgets/text-control-flow-root-ref.html b/tests/wpt/tests/html/rendering/widgets/text-control-flow-root-ref.html
new file mode 100644
index 00000000000..df2783540d8
--- /dev/null
+++ b/tests/wpt/tests/html/rendering/widgets/text-control-flow-root-ref.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<meta charset="UTF-8">
+
+<input id="input1">
+<br>
+<input style="transform: scale(0.5);">
+<br>
+aaa<input>aaa
+<br>
+<textarea></textarea>
+<br>
+<textarea style="transform: scale(0.5);"></textarea>
+<br>
+aa<textarea style="transform: scale(0.5);">aa</textarea>aa
diff --git a/tests/wpt/tests/html/rendering/widgets/text-control-flow-root.html b/tests/wpt/tests/html/rendering/widgets/text-control-flow-root.html
new file mode 100644
index 00000000000..54f7612da34
--- /dev/null
+++ b/tests/wpt/tests/html/rendering/widgets/text-control-flow-root.html
@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<meta charset="UTF-8">
+<title>display inside of text control should always be flow-root</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/rendering.html#form-controls">
+<link rel=match href="text-control-flow-root-ref.html">
+
+<input id="input1" style="display: inline;">
+<br>
+<input style="display: inline; transform: scale(0.5);">
+<br>
+aaa<input style="display: inline;">aaa
+<br>
+<textarea style="display: inline;"></textarea>
+<br>
+<textarea style="display: inline; transform: scale(0.5);"></textarea>
+<br>
+aa<textarea style="display: inline; transform: scale(0.5);">aa</textarea>aa