According to Tom Hacohen this was breaking build with some compilers.
In file included from hb-buffer-private.hh:35:0,
from hb-ot-map-private.hh:32,
from hb-ot-shape-private.hh:32,
from hb-ot-shape.cc:29:
hb-object-private.hh: In constructor '_hb_object_header_t::_hb_object_header_t()':
hb-object-private.hh:97:8: error: uninitialized const member in 'struct hb_reference_count_t'
hb-object-private.hh:51:25: note: 'hb_reference_count_t::ref_count' should be initialized
In file included from hb-ot-shape.cc:33:0:
hb-set-private.hh: In constructor '_hb_set_t::_hb_set_t()':
hb-set-private.hh:37:8: note: synthesized method '_hb_object_header_t::_hb_object_header_t()' first required here
hb-ot-shape.cc: In function 'void hb_ot_shape_glyphs_closure(hb_font_t*, hb_buffer_t*, const hb_feature_t*, unsigned int, hb_set_t*)':
hb-ot-shape.cc:521:12: note: synthesized method '_hb_set_t::_hb_set_t()' first required here
Computes all the glyphs that may be generated given a font and
set of Unicode characters.
The order of the Unicode characters is irrelevant.
Sample output:
behdad:util 0$ ./hb-ot-shape-closure Doulos\ SIL\ Regular.ttf f
f f_f
behdad:util 0$ ./hb-ot-shape-closure Doulos\ SIL\ Regular.ttf i
i
behdad:util 0$ ./hb-ot-shape-closure Doulos\ SIL\ Regular.ttf fi
f f_i f_f_i f_f i
behdad:util 0$ ./hb-ot-shape-closure DroidNaskh-Regular.ttf ب
uni0628 uni0628.init uni0628.medi uni0628.fina
behdad:util 0$ ./hb-ot-shape-closure DroidNaskh-Regular.ttf ا
uni0627 uni0627.fina
behdad:util 0$ ./hb-ot-shape-closure DroidNaskh-Regular.ttf با
uni0627 uni0627.fina uni0628 uni0628.init uni0628.medi uni0628.fina
behdad:util 0$ ./hb-ot-shape-closure DroidNaskh-Regular.ttf با --no-glyph-names
5 6 133 134 135 136
Behdad Esfahbod