[buffer] Clean up internal state bookkeeping

hb_buffer_reset() was NOT resetting cluster_level. Ouch! Fix that.

Part of harfbuzz#1555

src/hb-buffer.cc

@@ -261,6 +261,7 @@ hb_buffer_t::reset ()
   hb_unicode_funcs_destroy (unicode);
   unicode = hb_unicode_funcs_reference (hb_unicode_funcs_get_default ());
   flags = HB_BUFFER_FLAG_DEFAULT;
+  cluster_level = HB_BUFFER_CLUSTER_LEVEL_DEFAULT;
   replacement = HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT;
   invisible = 0;
   not_found = 0;
@@ -271,25 +272,26 @@ hb_buffer_t::reset ()
 void
 hb_buffer_t::clear ()
 {
+  content_type = HB_BUFFER_CONTENT_TYPE_INVALID;
   hb_segment_properties_t default_props = HB_SEGMENT_PROPERTIES_DEFAULT;
   props = default_props;
-  scratch_flags = HB_BUFFER_SCRATCH_FLAG_DEFAULT;
 
-  content_type = HB_BUFFER_CONTENT_TYPE_INVALID;
   successful = true;
   have_output = false;
   have_positions = false;
 
   idx = 0;
   len = 0;
   out_len = 0;
-  out_info = info;
 
-  serial = 0;
+  out_info = info;
 
   memset (context, 0, sizeof context);
   memset (context_len, 0, sizeof context_len);
 
+  scratch_flags = HB_BUFFER_SCRATCH_FLAG_DEFAULT;
+  serial = 0;
+
   deallocate_var_all ();
 }
 
@@ -604,12 +606,11 @@ DEFINE_NULL_INSTANCE (hb_buffer_t) =
   HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT,
   0, /* invisible */
   0, /* not_found */
-  HB_BUFFER_SCRATCH_FLAG_DEFAULT,
-  HB_BUFFER_MAX_LEN_DEFAULT,
-  HB_BUFFER_MAX_OPS_DEFAULT,
+
 
   HB_BUFFER_CONTENT_TYPE_INVALID,
   HB_SEGMENT_PROPERTIES_DEFAULT,
+
   false, /* successful */
   false, /* have_output */
   true  /* have_positions */

src/hb-buffer.hh

@@ -87,18 +87,21 @@ struct hb_buffer_t
 {
   hb_object_header_t header;
 
-  /* Information about how the text in the buffer should be treated */
+  /*
+   * Information about how the text in the buffer should be treated.
+   */
+
   hb_unicode_funcs_t *unicode; /* Unicode functions */
   hb_buffer_flags_t flags; /* BOT / EOT / etc. */
   hb_buffer_cluster_level_t cluster_level;
   hb_codepoint_t replacement; /* U+FFFD or something else. */
   hb_codepoint_t invisible; /* 0 or something else. */
   hb_codepoint_t not_found; /* 0 or something else. */
-  hb_buffer_scratch_flags_t scratch_flags; /* Have space-fallback, etc. */
-  unsigned int max_len; /* Maximum allowed len. */
-  int max_ops; /* Maximum allowed operations. */
 
-  /* Buffer contents */
+  /*
+   * Buffer contents
+   */
+
   hb_buffer_content_type_t content_type;
   hb_segment_properties_t props; /* Script, language, direction */
 
@@ -115,15 +118,23 @@ struct hb_buffer_t
   hb_glyph_info_t     *out_info;
   hb_glyph_position_t *pos;
 
-  unsigned int serial;
-
   /* Text before / after the main buffer contents.
    * Always in Unicode, and ordered outward.
    * Index 0 is for "pre-context", 1 for "post-context". */
   static constexpr unsigned CONTEXT_LENGTH = 5u;
   hb_codepoint_t context[2][CONTEXT_LENGTH];
   unsigned int context_len[2];
 
+  /*
+   * Not part of content.
+   */
+
+  hb_buffer_scratch_flags_t scratch_flags; /* Have space-fallback, etc. */
+  unsigned int serial;
+
+  unsigned int max_len; /* Maximum allowed len. */
+  int max_ops; /* Maximum allowed operations. */
+
   /* Debugging API */
 #ifndef HB_NO_BUFFER_MESSAGE
   hb_buffer_message_func_t message_func;