From e2a2b5b229c92f1de3b9c3ea111cd1ffa75b18fc Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Thu, 10 Aug 2017 20:10:12 -0700
Subject: [PATCH] [unsafe-to-break] Be careful with flag propagation when
 merging clusters

---
 src/hb-buffer-private.hh | 13 +++++++++++++
 src/hb-buffer.cc         | 17 ++++++++++-------
 src/hb-ot-shape.cc       |  3 ++-
 3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/hb-buffer-private.hh b/src/hb-buffer-private.hh
index e598f9e1a..01972af65 100644
--- a/src/hb-buffer-private.hh
+++ b/src/hb-buffer-private.hh
@@ -288,6 +288,19 @@ struct hb_buffer_t {
     return ret;
   }
   HB_INTERNAL bool message_impl (hb_font_t *font, const char *fmt, va_list ap) HB_PRINTF_FUNC(3, 0);
+
+  static inline void
+  set_cluster (hb_glyph_info_t &info, unsigned int cluster, unsigned int mask = 0)
+  {
+    if (info.cluster != cluster)
+    {
+      if (mask & HB_GLYPH_FLAG_UNSAFE_TO_BREAK)
+	info.mask |= HB_GLYPH_FLAG_UNSAFE_TO_BREAK;
+      else
+	info.mask &= ~HB_GLYPH_FLAG_UNSAFE_TO_BREAK;
+    }
+    info.cluster = cluster;
+  }
 };
 
 
diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 2fcb06dab..4b0f96035 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -552,7 +552,7 @@ hb_buffer_t::merge_clusters_impl (unsigned int start,
   if (cluster_level == HB_BUFFER_CLUSTER_LEVEL_CHARACTERS)
     return;
 
-  uint32_t cluster = info[start].cluster;
+  unsigned int cluster = info[start].cluster;
 
   for (unsigned int i = start + 1; i < end; i++)
     cluster = MIN (cluster, info[i].cluster);
@@ -568,10 +568,10 @@ hb_buffer_t::merge_clusters_impl (unsigned int start,
   /* If we hit the start of buffer, continue in out-buffer. */
   if (idx == start)
     for (unsigned int i = out_len; i && out_info[i - 1].cluster == info[start].cluster; i--)
-      out_info[i - 1].cluster = cluster;
+      set_cluster (out_info[i - 1], cluster);
 
   for (unsigned int i = start; i < end; i++)
-    info[i].cluster = cluster;
+    set_cluster (info[i], cluster);
 }
 void
 hb_buffer_t::merge_out_clusters (unsigned int start,
@@ -583,7 +583,7 @@ hb_buffer_t::merge_out_clusters (unsigned int start,
   if (unlikely (end - start < 2))
     return;
 
-  uint32_t cluster = out_info[start].cluster;
+  unsigned int cluster = out_info[start].cluster;
 
   for (unsigned int i = start + 1; i < end; i++)
     cluster = MIN (cluster, out_info[i].cluster);
@@ -599,14 +599,16 @@ hb_buffer_t::merge_out_clusters (unsigned int start,
   /* If we hit the end of out-buffer, continue in buffer. */
   if (end == out_len)
     for (unsigned int i = idx; i < len && info[i].cluster == out_info[end - 1].cluster; i++)
-      info[i].cluster = cluster;
+      set_cluster (info[i], cluster);
 
   for (unsigned int i = start; i < end; i++)
-    out_info[i].cluster = cluster;
+    set_cluster (out_info[i], cluster);
 }
 void
 hb_buffer_t::delete_glyph ()
 {
+  /* The logic here is duplicated in hb_ot_hide_default_ignorables(). */
+
   unsigned int cluster = info[idx].cluster;
   if (idx + 1 < len && cluster == info[idx + 1].cluster)
   {
@@ -619,9 +621,10 @@ hb_buffer_t::delete_glyph ()
     /* Merge cluster backward. */
     if (cluster < out_info[out_len - 1].cluster)
     {
+      unsigned int mask = info[idx].mask;
       unsigned int old_cluster = out_info[out_len - 1].cluster;
       for (unsigned i = out_len; i && out_info[i - 1].cluster == old_cluster; i--)
-	out_info[i - 1].cluster = cluster;
+	set_cluster (out_info[i - 1], cluster, mask);
     }
     goto done;
   }
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 29f5e58e5..5cd69927e 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -509,9 +509,10 @@ hb_ot_hide_default_ignorables (hb_ot_shape_context_t *c)
 	  /* Merge cluster backward. */
 	  if (cluster < info[j - 1].cluster)
 	  {
+	    unsigned int mask = info[i].mask;
 	    unsigned int old_cluster = info[j - 1].cluster;
 	    for (unsigned k = j; k && info[k - 1].cluster == old_cluster; k--)
-	      info[k - 1].cluster = cluster;
+	      buffer->set_cluster (info[k - 1], cluster, mask);
 	  }
 	  continue;
 	}