From d26a0dcf3071ee428b3b4c436a0d156d3efcfe0d Mon Sep 17 00:00:00 2001
From: Khaled Hosny <khaled@aliftype.com>
Date: Sun, 2 Apr 2023 15:47:33 +0200
Subject: itemize: Improve script itemization

Merge marks, and other cluster extenders with the previous script. Logic
copied from:
https://searchfox.org/mozilla-central/rev/dbc0cd5615f9cd7337d3e05b7c3925af5f35c0ee/gfx/thebes/gfxScriptItemizer.cpp#113-122

Handling of script extensions is still missing as GLib does not seem to
have an API to retrieve it.

Fixes https://gitlab.gnome.org/GNOME/pango/-/issues/739
---
 pango/pango-script.c         | 23 ++++++++++++++++++++---
 tests/itemize/three.expected |  9 +++++++++
 tests/itemize/three.items    |  1 +
 3 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 tests/itemize/three.expected
 create mode 100644 tests/itemize/three.items

diff --git a/pango/pango-script.c b/pango/pango-script.c
index 71c519fd..fa9ab21d 100644
--- a/pango/pango-script.c
+++ b/pango/pango-script.c
@@ -286,12 +286,29 @@ get_pair_index (gunichar ch)
   return -1;
 }
 
+static gboolean
+is_cluster_extender (gunichar ch)
+{
+  GUnicodeType type = g_unichar_type (ch);
+  return (type >= G_UNICODE_SPACING_MARK && type <= G_UNICODE_NON_SPACING_MARK) ||
+	 (ch >= 0x200C && ch <= 0x200D) ||    /* ZWJ, ZWNJ */
+	 (ch >= 0xFF9E && ch <= 0xFF9F) ||    /* katakana sound marks */
+	 (ch >= 0x1F3FB && ch <= 0x1F3FF) ||  /* fitzpatrick skin tone modifiers */
+	 (ch >= 0xE0020 && ch <= 0xE007F);    /* emoji (flag) tag characters */
+}
+
 /* duplicated in pango-language.c */
 #define REAL_SCRIPT(script) \
   ((script) > PANGO_SCRIPT_INHERITED && (script) != PANGO_SCRIPT_UNKNOWN)
 
-#define SAME_SCRIPT(script1, script2) \
-  (!REAL_SCRIPT (script1) || !REAL_SCRIPT (script2) || (script1) == (script2))
+#define IS_CLUSTER_EXTENDER(ch) \
+  g_unichar_type (ch)
+
+/* TODO: Use Unicode ScriptExtensions */
+#define SAME_SCRIPT(script1, script2, ch) \
+  (!REAL_SCRIPT (script1) || !REAL_SCRIPT (script2) || \
+   (script1) == (script2) || \
+   is_cluster_extender (ch))
 
 #define IS_OPEN(pair_index) (((pair_index) & 1) == 0)
 
@@ -372,7 +389,7 @@ pango_script_iter_next (PangoScriptIter *iter)
 	    }
 	}
 
-      if (SAME_SCRIPT (iter->script_code, sc))
+      if (SAME_SCRIPT (iter->script_code, sc, ch))
 	{
 	  if (!REAL_SCRIPT (iter->script_code) && REAL_SCRIPT (sc))
 	    {
diff --git a/tests/itemize/three.expected b/tests/itemize/three.expected
new file mode 100644
index 00000000..eb45fbd3
--- /dev/null
+++ b/tests/itemize/three.expected
@@ -0,0 +1,9 @@
+<span font="Cantarell 11" fallback="false">عַرַبִ</span>
+
+Items:  عַرַبִ       
+Chars:  6(0)               
+Font:   Cantarell 11       
+Script: arabic             
+Lang:   ar                 
+Bidi:   1                  
+Attrs:  0 12 fallback false
diff --git a/tests/itemize/three.items b/tests/itemize/three.items
new file mode 100644
index 00000000..394767e5
--- /dev/null
+++ b/tests/itemize/three.items
@@ -0,0 +1 @@
+<span font="Cantarell 11" fallback="false">عַرַبִ</span>
-- 
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