[machinery] Allow using lazy-loader with void*

Fixes https://github.com/harfbuzz/harfbuzz/issues/3427

src/Makefile.am

@@ -345,7 +345,9 @@ test_gsub_would_substitute_LDADD = libharfbuzz.la $(HBLIBS) $(FREETYPE_LIBS)
 COMPILED_TESTS = \
 	test-algs \
 	test-array \
+	test-bimap \
 	test-iter \
+	test-machinery \
 	test-map \
 	test-number \
 	test-ot-tag \
@@ -354,7 +356,6 @@ COMPILED_TESTS = \
 	test-serialize \
 	test-unicode-ranges \
 	test-vector \
-	test-bimap \
 	test-repacker \
 	$(NULL)
 COMPILED_TESTS_CPPFLAGS = $(HBCFLAGS) -DMAIN -UNDEBUG
@@ -370,18 +371,18 @@ test_array_SOURCES = test-array.cc
 test_array_CPPFLAGS = $(HBCFLAGS)
 test_array_LDADD = libharfbuzz.la $(HBLIBS)
 
-test_priority_queue_SOURCES = test-priority-queue.cc hb-static.cc
+test_bimap_SOURCES = test-bimap.cc hb-static.cc
-test_priority_queue_CPPFLAGS = $(HBCFLAGS)
+test_bimap_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
-test_priority_queue_LDADD = libharfbuzz.la $(HBLIBS)
+test_bimap_LDADD = $(COMPILED_TESTS_LDADD)
-
-test_repacker_SOURCES = test-repacker.cc hb-static.cc
-test_repacker_CPPFLAGS = $(HBCFLAGS)
-test_repacker_LDADD = libharfbuzz.la libharfbuzz-subset.la $(HBLIBS)
 
 test_iter_SOURCES = test-iter.cc hb-static.cc
 test_iter_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_iter_LDADD = $(COMPILED_TESTS_LDADD)
 
+test_machinery_SOURCES = test-machinery.cc hb-static.cc
+test_machinery_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
+test_machinery_LDADD = $(COMPILED_TESTS_LDADD)
+
 test_map_SOURCES = test-map.cc hb-static.cc
 test_map_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_map_LDADD = $(COMPILED_TESTS_LDADD)
@@ -394,6 +395,14 @@ test_ot_tag_SOURCES = hb-ot-tag.cc
 test_ot_tag_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_ot_tag_LDADD = $(COMPILED_TESTS_LDADD)
 
+test_priority_queue_SOURCES = test-priority-queue.cc hb-static.cc
+test_priority_queue_CPPFLAGS = $(HBCFLAGS)
+test_priority_queue_LDADD = libharfbuzz.la $(HBLIBS)
+
+test_repacker_SOURCES = test-repacker.cc hb-static.cc
+test_repacker_CPPFLAGS = $(HBCFLAGS)
+test_repacker_LDADD = libharfbuzz.la libharfbuzz-subset.la $(HBLIBS)
+
 test_set_SOURCES = test-set.cc hb-static.cc
 test_set_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_set_LDADD = $(COMPILED_TESTS_LDADD)
@@ -410,10 +419,6 @@ test_vector_SOURCES = test-vector.cc hb-static.cc
 test_vector_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
 test_vector_LDADD = $(COMPILED_TESTS_LDADD)
 
-test_bimap_SOURCES = test-bimap.cc hb-static.cc
-test_bimap_CPPFLAGS = $(COMPILED_TESTS_CPPFLAGS)
-test_bimap_LDADD = $(COMPILED_TESTS_LDADD)
-
 dist_check_SCRIPTS = \
 	check-c-linkage-decls.py \
 	check-externs.py \

src/hb-common.cc

@@ -1065,7 +1065,7 @@ hb_variation_from_string (const char *str, int len,
 static inline void free_static_C_locale ();
 
 static struct hb_C_locale_lazy_loader_t : hb_lazy_loader_t<hb_remove_pointer<hb_locale_t>,
-							     hb_C_locale_lazy_loader_t>
+							   hb_C_locale_lazy_loader_t>
 {
   static hb_locale_t create ()
   {

src/hb-machinery.hh

@@ -194,7 +194,8 @@ struct hb_lazy_loader_t : hb_data_wrapper_t<Data, WheresData>
   }
 
   const Returned * operator -> () const { return get (); }
-  const Returned & operator * () const  { return *get (); }
+  template <typename U = Returned, hb_enable_if (!hb_is_same (U, void))>
+  const U & operator * () const  { return *get (); }
   explicit operator bool () const
   { return get_stored () != Funcs::get_null (); }
   template <typename C> operator const C * () const { return get (); }

src/meson.build

@@ -485,12 +485,13 @@ if get_option('tests').enabled()
   compiled_tests = {
     'test-algs': ['test-algs.cc', 'hb-static.cc'],
     'test-array': ['test-array.cc'],
-    'test-repacker': ['test-repacker.cc', 'hb-static.cc'],
-    'test-priority-queue': ['test-priority-queue.cc', 'hb-static.cc'],
     'test-iter': ['test-iter.cc', 'hb-static.cc'],
+    'test-machinery': ['test-machinery.cc', 'hb-static.cc'],
     'test-map': ['test-map.cc', 'hb-static.cc'],
     'test-number': ['test-number.cc', 'hb-number.cc'],
     'test-ot-tag': ['hb-ot-tag.cc'],
+    'test-priority-queue': ['test-priority-queue.cc', 'hb-static.cc'],
+    'test-repacker': ['test-repacker.cc', 'hb-static.cc'],
     'test-set': ['test-set.cc', 'hb-static.cc'],
     'test-serialize': ['test-serialize.cc', 'hb-static.cc'],
     'test-unicode-ranges': ['test-unicode-ranges.cc'],

src/test-machinery.cc

@@ -0,0 +1,46 @@
+/*
+ * Copyright © 2022  Behdad Esfahbod
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ */
+
+#include "hb.hh"
+#include "hb-machinery.hh"
+
+struct hb_intp_lazy_loader_t : hb_lazy_loader_t<int, hb_intp_lazy_loader_t>
+{
+  static int* create () { return nullptr; }
+  static void destroy (int* l) {}
+  static int* get_null () { return nullptr; }
+};
+
+struct hb_void_lazy_loader_t : hb_lazy_loader_t<void, hb_void_lazy_loader_t>
+{
+  static void* create () { return nullptr; }
+  static void destroy (void* l) {}
+  static void* get_null () { return nullptr; }
+};
+
+int
+main (int argc, char **argv)
+{
+  return 0;
+}