LibUnicode: Skip over emoji sequences in grapheme boundary segmentation

Emoji sequences in the grapheme segmentation spec are a bit tricky:

    \p{Extended_Pictographic} Extend* ZWJ × \p{Extended_Pictographic}

Our current strategy of tracking a boolean to indicate if we are in an
emoji sequence was causing us to break up emoji made of multiple sub-
sequences. For example, in the "family: man, woman, girl, boy" sequence:

    U+1F468 U+200D U+1F469 U+200D U+1F467 U+200D U+1F466

We would break at indices 0 (correctly) and 6 (incorrectly).

Instead of tracking a boolean, it's quite a bit simpler to reason about
emoji sequences by just skipping past them entirely. Note that in cases
like the above emoji, we skip one sub-sequence at a time.

1 files changed, 19 insertions, 12 deletions

diff --git a/Userland/Libraries/LibUnicode/Segmentation.cpp b/Userland/Libraries/LibUnicode/Segmentation.cpp
index 47715efe84..750f52907a 100644
--- a/Userland/Libraries/LibUnicode/Segmentation.cpp
+++ b/Userland/Libraries/LibUnicode/Segmentation.cpp
@@ -64,13 +64,30 @@ static void for_each_grapheme_segmentation_boundary_impl([[maybe_unused]] ViewTy
     if (code_unit_length(view) > 1) {
         auto it = view.begin();
         auto code_point = *it;
-        u32 next_code_point;
+        u32 next_code_point = 0;
         auto current_ri_chain = 0;
-        auto in_emoji_sequence = false;
 
         for (++it; it != view.end(); ++it, code_point = next_code_point) {
             next_code_point = *it;
 
+            // GB11
+            if (code_point_has_property(code_point, Property::Extended_Pictographic) && has_any_gbp(next_code_point, GBP::Extend, GBP::ZWJ)) {
+                auto it_copy = it;
+
+                while (it_copy != view.end() && has_any_gbp(*it_copy, GBP::Extend))
+                    ++it_copy;
+
+                if (it_copy != view.end() && has_any_gbp(*it_copy, GBP::ZWJ)) {
+                    ++it_copy;
+
+                    if (it_copy != view.end() && code_point_has_property(*it_copy, Property::Extended_Pictographic)) {
+                        next_code_point = *it_copy;
+                        it = it_copy;
+                        continue;
+                    }
+                }
+            }
+
             auto code_point_is_cr = has_any_gbp(code_point, GBP::CR);
             auto next_code_point_is_lf = has_any_gbp(next_code_point, GBP::LF);
 
@@ -97,12 +114,6 @@ static void for_each_grapheme_segmentation_boundary_impl([[maybe_unused]] ViewTy
             if (next_code_point_is_t && has_any_gbp(code_point, GBP::LVT, GBP::T))
                 continue;
 
-            auto code_point_is_zwj = has_any_gbp(code_point, GBP::ZWJ);
-            if (!in_emoji_sequence && code_point_has_property(code_point, Property::Extended_Pictographic))
-                in_emoji_sequence = true;
-            else if (in_emoji_sequence && !has_any_gbp(code_point, GBP::Extend) && !code_point_is_zwj)
-                in_emoji_sequence = false;
-
             // GB9
             if (has_any_gbp(next_code_point, GBP::Extend, GBP::ZWJ))
                 continue;
@@ -113,10 +124,6 @@ static void for_each_grapheme_segmentation_boundary_impl([[maybe_unused]] ViewTy
             if (has_any_gbp(code_point, GBP::Prepend))
                 continue;
 
-            // GB11
-            if (in_emoji_sequence && code_point_is_zwj && code_point_has_property(next_code_point, Property::Extended_Pictographic))
-                continue;
-
             auto code_point_is_ri = has_any_gbp(code_point, GBP::Regional_Indicator);
             current_ri_chain = code_point_is_ri ? current_ri_chain + 1 : 0;