LibWeb: Iterate over text chunks using a grapheme-aware segmenter

Our current text iterator is not aware of multi-code point graphemes.
Instead of simply incrementing an iterator one code point at a time, use
our Unicode grapheme segmenter to break text into fragments.

(cherry picked from commit f0105b473b9cc3446ec36359b559db9a8e78446d;
amended as usual for Unicode::Segmenter -> Locale::Segmenter, and to
tweak expected/multi-code-point-graphemes.txt for serenity's superior
emoji glyphs)

Tests/LibWeb/Layout/expected/multi-code-point-graphemes.txt

@@ -0,0 +1,34 @@
+Viewport <#document> at (0,0) content-size 800x600 children: not-inline
+  BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
+    BlockContainer <body> at (8,16) content-size 784x83 children: not-inline
+      BlockContainer <p> at (8,16) content-size 784x17 children: inline
+        frag 0 from TextNode start: 0, length: 11, rect: [8,16 12.796875x17] baseline: 13.296875
+            "🧑‍🚒"
+        TextNode <#text>
+      BlockContainer <(anonymous)> at (8,49) content-size 784x0 children: inline
+        TextNode <#text>
+      BlockContainer <p> at (8,49) content-size 784x17 children: inline
+        frag 0 from TextNode start: 0, length: 13, rect: [8,49 11.203125x17] baseline: 13.296875
+            "🏴‍☠️"
+        TextNode <#text>
+      BlockContainer <(anonymous)> at (8,82) content-size 784x0 children: inline
+        TextNode <#text>
+      BlockContainer <p> at (8,82) content-size 784x17 children: inline
+        frag 0 from TextNode start: 0, length: 25, rect: [8,82 16x17] baseline: 13.296875
+            "🧑‍🧑‍🧒‍🧒"
+        TextNode <#text>
+      BlockContainer <(anonymous)> at (8,115) content-size 784x0 children: inline
+        TextNode <#text>
+
+ViewportPaintable (Viewport<#document>) [0,0 800x600]
+  PaintableWithLines (BlockContainer<HTML>) [0,0 800x600]
+    PaintableWithLines (BlockContainer<BODY>) [8,16 784x83] overflow: [8,16 784x99]
+      PaintableWithLines (BlockContainer<P>) [8,16 784x17]
+        TextPaintable (TextNode<#text>)
+      PaintableWithLines (BlockContainer(anonymous)) [8,49 784x0]
+      PaintableWithLines (BlockContainer<P>) [8,49 784x17]
+        TextPaintable (TextNode<#text>)
+      PaintableWithLines (BlockContainer(anonymous)) [8,82 784x0]
+      PaintableWithLines (BlockContainer<P>) [8,82 784x17]
+        TextPaintable (TextNode<#text>)
+      PaintableWithLines (BlockContainer(anonymous)) [8,115 784x0]

Tests/LibWeb/Layout/input/multi-code-point-graphemes.html

@@ -0,0 +1,3 @@
+<p>🧑‍🚒</p>
+<p>🏴‍☠️</p>
+<p>🧑‍🧑‍🧒‍🧒</p>

Userland/Libraries/LibWeb/Layout/TextNode.cpp

@@ -391,13 +391,14 @@ void TextNode::compute_text_for_rendering()
     m_text_for_rendering = MUST(builder.to_string());
 }
 
-TextNode::ChunkIterator::ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const& font_cascade_list)
+TextNode::ChunkIterator::ChunkIterator(String const& text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const& font_cascade_list)
     : m_wrap_lines(wrap_lines)
     , m_respect_linebreaks(respect_linebreaks)
     , m_utf8_view(text)
-    , m_iterator(m_utf8_view.begin())
     , m_font_cascade_list(font_cascade_list)
+    , m_segmenter(Locale::Segmenter::create(Locale::SegmenterGranularity::Grapheme))
 {
+    m_segmenter->set_segmented_text(text);
 }
 
 static Gfx::GlyphRun::TextType text_type_for_code_point(u32 code_point)
@@ -462,75 +463,85 @@ Optional<TextNode::Chunk> TextNode::ChunkIterator::peek(size_t count)
 
 Optional<TextNode::Chunk> TextNode::ChunkIterator::next_without_peek()
 {
-    if (m_iterator == m_utf8_view.end())
+    if (m_current_index >= m_utf8_view.byte_length())
         return {};
 
-    auto start_of_chunk = m_iterator;
+    auto current_code_point = [this]() {
+        return *m_utf8_view.iterator_at_byte_offset_without_validation(m_current_index);
+    };
+    auto next_grapheme_boundary = [this]() {
+        return m_segmenter->next_boundary(m_current_index).value_or(m_utf8_view.byte_length());
+    };
 
-    Gfx::Font const& font = m_font_cascade_list.font_for_code_point(*m_iterator);
-    auto text_type = text_type_for_code_point(*m_iterator);
-    while (m_iterator != m_utf8_view.end()) {
-        if (&font != &m_font_cascade_list.font_for_code_point(*m_iterator)) {
-            if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value())
+    auto code_point = current_code_point();
+    auto start_of_chunk = m_current_index;
+
+    Gfx::Font const& font = m_font_cascade_list.font_for_code_point(code_point);
+    auto text_type = text_type_for_code_point(code_point);
+
+    while (m_current_index < m_utf8_view.byte_length()) {
+        code_point = current_code_point();
+
+        if (&font != &m_font_cascade_list.font_for_code_point(code_point)) {
+            if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
                 return result.release_value();
         }
 
-        if (m_respect_linebreaks && *m_iterator == '\n') {
+        if (m_respect_linebreaks && code_point == '\n') {
             // Newline encountered, and we're supposed to preserve them.
             // If we have accumulated some code points in the current chunk, commit them now and continue with the newline next time.
-            if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value())
+            if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
                 return result.release_value();
 
             // Otherwise, commit the newline!
-            ++m_iterator;
-            auto result = try_commit_chunk(start_of_chunk, m_iterator, true, font, text_type);
+            m_current_index = next_grapheme_boundary();
+            auto result = try_commit_chunk(start_of_chunk, m_current_index, true, font, text_type);
             VERIFY(result.has_value());
             return result.release_value();
         }
 
         if (m_wrap_lines) {
-            if (text_type != text_type_for_code_point(*m_iterator)) {
-                if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value())
+            if (text_type != text_type_for_code_point(code_point)) {
+                if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value()) {
                     return result.release_value();
+                }
             }
 
-            if (is_ascii_space(*m_iterator)) {
+            if (is_ascii_space(code_point)) {
                 // Whitespace encountered, and we're allowed to break on whitespace.
                 // If we have accumulated some code points in the current chunk, commit them now and continue with the whitespace next time.
-                if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value())
+                if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value()) {
                     return result.release_value();
+                }
 
                 // Otherwise, commit the whitespace!
-                ++m_iterator;
-                if (auto result = try_commit_chunk(start_of_chunk, m_iterator, false, font, text_type); result.has_value())
+                m_current_index = next_grapheme_boundary();
+                if (auto result = try_commit_chunk(start_of_chunk, m_current_index, false, font, text_type); result.has_value())
                     return result.release_value();
                 continue;
             }
         }
 
-        ++m_iterator;
+        m_current_index = next_grapheme_boundary();
     }
 
-    if (start_of_chunk != m_utf8_view.end()) {
+    if (start_of_chunk != m_utf8_view.byte_length()) {
         // Try to output whatever's left at the end of the text node.
-        if (auto result = try_commit_chunk(start_of_chunk, m_utf8_view.end(), false, font, text_type); result.has_value())
+        if (auto result = try_commit_chunk(start_of_chunk, m_utf8_view.byte_length(), false, font, text_type); result.has_value())
             return result.release_value();
     }
 
     return {};
 }
 
-Optional<TextNode::Chunk> TextNode::ChunkIterator::try_commit_chunk(Utf8View::Iterator const& start, Utf8View::Iterator const& end, bool has_breaking_newline, Gfx::Font const& font, Gfx::GlyphRun::TextType text_type) const
+Optional<TextNode::Chunk> TextNode::ChunkIterator::try_commit_chunk(size_t start, size_t end, bool has_breaking_newline, Gfx::Font const& font, Gfx::GlyphRun::TextType text_type) const
 {
-    auto byte_offset = m_utf8_view.byte_offset_of(start);
-    auto byte_length = m_utf8_view.byte_offset_of(end) - byte_offset;
-
-    if (byte_length > 0) {
-        auto chunk_view = m_utf8_view.substring_view(byte_offset, byte_length);
+    if (auto byte_length = end - start; byte_length > 0) {
+        auto chunk_view = m_utf8_view.substring_view(start, byte_length);
         return Chunk {
             .view = chunk_view,
             .font = font,
-            .start = byte_offset,
+            .start = start,
             .length = byte_length,
             .has_breaking_newline = has_breaking_newline,
             .is_all_whitespace = is_all_whitespace(chunk_view.as_string()),

Userland/Libraries/LibWeb/Layout/TextNode.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/Utf8View.h>
+#include <LibLocale/Segmenter.h>
 #include <LibWeb/DOM/Text.h>
 #include <LibWeb/Layout/Node.h>
 
@@ -38,20 +39,23 @@ public:
 
     class ChunkIterator {
     public:
-        ChunkIterator(StringView text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const&);
+        ChunkIterator(String const& text, bool wrap_lines, bool respect_linebreaks, Gfx::FontCascadeList const&);
+
         Optional<Chunk> next();
         Optional<Chunk> peek(size_t);
 
     private:
         Optional<Chunk> next_without_peek();
-        Optional<Chunk> try_commit_chunk(Utf8View::Iterator const& start, Utf8View::Iterator const& end, bool has_breaking_newline, Gfx::Font const&, Gfx::GlyphRun::TextType) const;
+        Optional<Chunk> try_commit_chunk(size_t start, size_t end, bool has_breaking_newline, Gfx::Font const&, Gfx::GlyphRun::TextType) const;
 
         bool const m_wrap_lines;
         bool const m_respect_linebreaks;
         Utf8View m_utf8_view;
-        Utf8View::Iterator m_iterator;
         Gfx::FontCascadeList const& m_font_cascade_list;
 
+        NonnullOwnPtr<Locale::Segmenter> m_segmenter;
+        size_t m_current_index { 0 };
+
         Vector<Chunk> m_peek_queue;
     };