From c369f68effcaa049bd404724b3693412cd48b69f Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Thu, 14 Aug 2025 15:25:19 -0400
Subject: [PATCH] LibWeb: Delete entire graphemes when the delete/backspace key
 is pressed

We currently delete a single code unit. If the user presses backspace on
a multi code point emoji, they are going to expect the entire emoji to
be removed. This now matches the behavior of Chrome and Firefox.
---
 Libraries/LibWeb/Editing/Commands.cpp         | 14 +++++++---
 .../LibWeb/HTML/FormAssociatedElement.cpp     |  9 +++----
 .../expected/Editing/execCommand-delete.txt   |  4 +++
 .../Editing/execCommand-forwardDelete.txt     |  3 +++
 Tests/LibWeb/Text/expected/input-delete.txt   |  6 +++++
 .../input/Editing/execCommand-delete.html     | 26 ++++++++++++-------
 .../Editing/execCommand-forwardDelete.html    |  2 ++
 Tests/LibWeb/Text/input/input-delete.html     | 24 +++++++++++++++++
 8 files changed, 69 insertions(+), 19 deletions(-)
 create mode 100644 Tests/LibWeb/Text/expected/input-delete.txt
 create mode 100644 Tests/LibWeb/Text/input/input-delete.html

diff --git a/Libraries/LibWeb/Editing/Commands.cpp b/Libraries/LibWeb/Editing/Commands.cpp
index 1defb51e07c..6f6260cec75 100644
--- a/Libraries/LibWeb/Editing/Commands.cpp
+++ b/Libraries/LibWeb/Editing/Commands.cpp
@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibUnicode/Segmenter.h>
 #include <LibWeb/CSS/StyleValues/KeywordStyleValue.h>
 #include <LibWeb/DOM/Comment.h>
 #include <LibWeb/DOM/Document.h>
@@ -204,12 +205,17 @@ bool command_delete_action(DOM::Document& document, Utf16String const&)
             block_node_child_is_relevant_type = child_element.local_name().is_one_of(HTML::TagNames::br, HTML::TagNames::hr, HTML::TagNames::img);
         }
     }
-    if ((is<DOM::Text>(*node) && offset != 0) || block_node_child_is_relevant_type) {
+
+    if (auto const* text_node = as_if<DOM::Text>(*node); (text_node && offset != 0) || block_node_child_is_relevant_type) {
+        auto start_offset = text_node
+            ? text_node->grapheme_segmenter().previous_boundary(offset).value_or(offset - 1)
+            : offset - 1;
+
         // 1. Call collapse(node, offset) on the context object's selection.
         MUST(selection.collapse(node, offset));
 
         // 2. Call extend(node, offset − 1) on the context object's selection.
-        MUST(selection.extend(*node, offset - 1));
+        MUST(selection.extend(*node, start_offset));
 
         // 3. Delete the selection.
         delete_the_selection(selection);
@@ -927,9 +933,9 @@ bool command_forward_delete_action(DOM::Document& document, Utf16String const&)
     }
 
     // 5. If node is a Text node and offset is not node's length:
-    if (is<DOM::Text>(*node) && offset != node->length()) {
+    if (auto const* text_node = as_if<DOM::Text>(*node); text_node && offset != node->length()) {
         // 1. Let end offset be offset plus one.
-        auto end_offset = offset + 1;
+        auto end_offset = text_node->grapheme_segmenter().next_boundary(offset).value_or(offset + 1);
 
         // FIXME: 2. While end offset is not node's length and the end offsetth code unit of node's data has general category M
         //    when interpreted as a Unicode code point, add one to end offset.
diff --git a/Libraries/LibWeb/HTML/FormAssociatedElement.cpp b/Libraries/LibWeb/HTML/FormAssociatedElement.cpp
index ec3f2360000..b7cab2fe652 100644
--- a/Libraries/LibWeb/HTML/FormAssociatedElement.cpp
+++ b/Libraries/LibWeb/HTML/FormAssociatedElement.cpp
@@ -829,13 +829,12 @@ void FormAssociatedTextControlElement::handle_delete(DeleteDirection direction)
 
     if (selection_start == selection_end) {
         if (direction == DeleteDirection::Backward) {
-            if (selection_start > 0)
-                MUST(set_range_text({}, selection_start - 1, selection_end, Bindings::SelectionMode::End));
+            if (auto offset = text_node->grapheme_segmenter().previous_boundary(m_selection_end); offset.has_value())
+                selection_start = *offset;
         } else {
-            if (selection_start < text_node->length_in_utf16_code_units())
-                MUST(set_range_text({}, selection_start, selection_end + 1, Bindings::SelectionMode::End));
+            if (auto offset = text_node->grapheme_segmenter().next_boundary(m_selection_end); offset.has_value())
+                selection_end = *offset;
         }
-        return;
     }
 
     MUST(set_range_text({}, selection_start, selection_end, Bindings::SelectionMode::End));
diff --git a/Tests/LibWeb/Text/expected/Editing/execCommand-delete.txt b/Tests/LibWeb/Text/expected/Editing/execCommand-delete.txt
index 5022da5f91a..2ecb7b918bb 100644
--- a/Tests/LibWeb/Text/expected/Editing/execCommand-delete.txt
+++ b/Tests/LibWeb/Text/expected/Editing/execCommand-delete.txt
@@ -1,2 +1,6 @@
+--- a ---
 Before: foobar
 After: fobar
+--- b ---
+Before: foo👩🏼‍❤️‍👨🏻bar
+After: foobar
diff --git a/Tests/LibWeb/Text/expected/Editing/execCommand-forwardDelete.txt b/Tests/LibWeb/Text/expected/Editing/execCommand-forwardDelete.txt
index 6a2750fb0d7..b84dcc67b50 100644
--- a/Tests/LibWeb/Text/expected/Editing/execCommand-forwardDelete.txt
+++ b/Tests/LibWeb/Text/expected/Editing/execCommand-forwardDelete.txt
@@ -19,3 +19,6 @@ After: a&nbsp; &nbsp; b
 --- g ---
 Before: &nbsp;&nbsp;b
 After: &nbsp;b
+--- h ---
+Before: foo👩🏼‍❤️‍👨🏻bar
+After: foobar
diff --git a/Tests/LibWeb/Text/expected/input-delete.txt b/Tests/LibWeb/Text/expected/input-delete.txt
new file mode 100644
index 00000000000..d96d5415048
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/input-delete.txt
@@ -0,0 +1,6 @@
+--- a ---
+Before: foo👩🏼‍❤️‍👨🏻bar
+After: foobar
+--- b ---
+Before: foo👩🏼‍❤️‍👨🏻bar
+After: foobar
diff --git a/Tests/LibWeb/Text/input/Editing/execCommand-delete.html b/Tests/LibWeb/Text/input/Editing/execCommand-delete.html
index 91f22511c88..ad456e0573b 100644
--- a/Tests/LibWeb/Text/input/Editing/execCommand-delete.html
+++ b/Tests/LibWeb/Text/input/Editing/execCommand-delete.html
@@ -1,19 +1,25 @@
 <!DOCTYPE html>
 <script src="../include.js"></script>
-<div contenteditable="true">foobar</div>
+<div id="a" contenteditable="true">foobar</div>
+<div id="b" contenteditable="true">foo👩🏼‍❤️‍👨🏻bar</div>
 <script>
     test(() => {
-        var divElm = document.querySelector('div');
-        println(`Before: ${divElm.textContent}`);
+        const testDelete = function (divId, position) {
+            println(`--- ${divId} ---`);
+            const divElm = document.querySelector(`div#${divId}`);
+            println(`Before: ${divElm.textContent}`);
 
-        // Put cursor after 'foo'
-        var range = document.createRange();
-        range.setStart(divElm.childNodes[0], 3);
-        getSelection().addRange(range);
+            // Place cursor
+            const node = divElm.childNodes[0];
+            getSelection().setBaseAndExtent(node, position, node, position);
 
-        // Press backspace
-        document.execCommand('delete');
+            // Press backspace
+            document.execCommand("delete");
 
-        println(`After: ${divElm.textContent}`);
+            println(`After: ${divElm.textContent}`);
+        };
+
+        testDelete("a", 3);
+        testDelete("b", 15);
     });
 </script>
diff --git a/Tests/LibWeb/Text/input/Editing/execCommand-forwardDelete.html b/Tests/LibWeb/Text/input/Editing/execCommand-forwardDelete.html
index 5a1a98adcdc..6b41c4181f1 100644
--- a/Tests/LibWeb/Text/input/Editing/execCommand-forwardDelete.html
+++ b/Tests/LibWeb/Text/input/Editing/execCommand-forwardDelete.html
@@ -7,6 +7,7 @@
 <div id="e" contenteditable="true">a&nbsp;&nbsp;&nbsp;&nbsp;b</div>
 <div id="f" contenteditable="true">a&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b</div>
 <div id="g" contenteditable="true">&nbsp;&nbsp;b</div>
+<div id="h" contenteditable="true">foo👩🏼‍❤️‍👨🏻bar</div>
 <script>
     test(() => {
         const testForwardDelete = function(divId, position) {
@@ -31,5 +32,6 @@
         testForwardDelete('e', 1);
         testForwardDelete('f', 1);
         testForwardDelete('g', 0);
+        testForwardDelete('h', 3);
     });
 </script>
diff --git a/Tests/LibWeb/Text/input/input-delete.html b/Tests/LibWeb/Text/input/input-delete.html
new file mode 100644
index 00000000000..50962101da2
--- /dev/null
+++ b/Tests/LibWeb/Text/input/input-delete.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<script src="include.js"></script>
+<input id="a" value="foo👩🏼‍❤️‍👨🏻bar" />
+<input id="b" value="foo👩🏼‍❤️‍👨🏻bar" />
+<script>
+    test(() => {
+        const testDelete = function (id, position, key) {
+            println(`--- ${id} ---`);
+            const input = document.querySelector(`input#${id}`);
+            println(`Before: ${input.value}`);
+
+            // Place cursor
+            input.setSelectionRange(position, position);
+
+            // Press backspace
+            internals.sendKey(input, key);
+
+            println(`After: ${input.value}`);
+        };
+
+        testDelete("a", 15, "Backspace");
+        testDelete("b", 3, "Delete");
+    });
+</script>