[unsafe-to-concat] Adjust Arabic-joining start boundary condition more

src/hb-ot-shape-complex-arabic.cc

@@ -321,9 +321,19 @@ arabic_joining (hb_buffer_t *buffer)
       info[prev].arabic_shaping_action() = entry->prev_action;
       buffer->unsafe_to_break (prev, i + 1);
     }
-    else if (2 <= state && state <= 5) /* States that have a possible prev_action. */
+    else
     {
-      buffer->unsafe_to_concat (prev, i + 1);
+      if (prev == UINT_MAX)
+      {
+        if (this_type >= JOINING_TYPE_R)
+	  buffer->unsafe_to_concat_from_outbuffer (0, i + 1);
+      }
+      else
+      {
+	if (this_type >= JOINING_TYPE_R ||
+	    (2 <= state && state <= 5) /* States that have a possible prev_action. */)
+	  buffer->unsafe_to_concat (prev, i + 1);
+      }
     }
 
     info[i].arabic_shaping_action() = entry->curr_action;

test/shape/data/in-house/Makefile.sources

@@ -59,6 +59,7 @@ TESTS = \
 	tests/tibetan-contractions-2.tests \
 	tests/tibetan-vowels.tests \
 	tests/tt-kern-gpos.tests \
+	tests/unsafe-to-concat.tests \
 	tests/use-indic3.tests \
 	tests/use-marchen.tests \
 	tests/use-syllable.tests \

test/shape/data/in-house/meson.build

@@ -59,6 +59,7 @@ in_house_tests_base = [
   'tibetan-contractions-2.tests',
   'tibetan-vowels.tests',
   'tt-kern-gpos.tests',
+  'unsafe-to-concat.tests',
   'use-indic3.tests',
   'use-marchen.tests',
   'use-syllable.tests',

test/shape/data/in-house/tests/unsafe-to-concat.tests

@@ -0,0 +1 @@
+../fonts/34da9aab7bee86c4dfc3b85e423435822fdf4b62.ttf;--show-flags;U+0628,U+200C,U+0628;[uni0628=1+993#2|uni0628=0+993#2]