Added minor fixes to build without errors with gcc 4.9.2

[inobelar]

First of all, I want to thank you for your work on compatibility with quite old compilers!

At work, I happen to use a rather ancient environment & compiler:

• gcc --version: gcc (Debian 4.9.2-10) 4.9.2
• gcc -dumpmachine: arm-linux-gnueabihf
• uname -srmio: Linux 4.1.15-g14db131-dirty armv7l unknown GNU/Linux.

When trying to compile the latest sources (current latest commit: b8121cc) I encountered several compilation errors, which I tried to solve in this pull request. Next, I describe the errors that occurred (in the order they occurred) and the way to solve them.

I build harfbuzz with pre-build freetype and icu with (deprecated) CMake in the next way:

$ cmake ../harfbuzz \
     -G "Unix Makefiles" \
     -D CMAKE_BUILD_TYPE:STRING=Release \
     -D CMAKE_INSTALL_PREFIX:PATH=`pwd`/../installed/harfbuzz/ \
     \
     -D BUILD_SHARED_LIBS=OFF \
     \
     -D HB_HAVE_FREETYPE=ON \
     -D HB_HAVE_GRAPHITE2=OFF \
     -D HB_HAVE_GLIB=OFF \
     -D HB_HAVE_ICU=ON \
     \
     -D CMAKE_PREFIX_PATH="`realpath ../installed/freetype/`;`realpath ../installed/icu/`" \
     -D CMAKE_CXX_FLAGS="${CMAKE_CXX_FLAGS} -DHB_NO_UCD -DHAVE_ICU_BUILTIN"

Output

-- The C compiler identification is GNU 4.9.2
-- The CXX compiler identification is GNU 4.9.2
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
WARNHarfBuzz has a Meson port and tries to migrate all the other build systems to it, please consider using it as we might remove our cmake port soon.
CMake Warning (dev) at CMakeLists.txt:78 (include):
  Policy CMP0148 is not set: The FindPythonInterp and FindPythonLibs modules
  are removed.  Run "cmake --help-policy CMP0148" for policy details.  Use
  the cmake_policy command to set the policy and suppress this warning.

This warning is for project developers.  Use -Wno-dev to suppress it.

-- Found PythonInterp: /usr/bin/python (found version "2.7.9") 
-- Looking for atexit
-- Looking for atexit - found
-- Looking for mprotect
-- Looking for mprotect - found
-- Looking for sysconf
-- Looking for sysconf - found
-- Looking for getpagesize
-- Looking for getpagesize - found
-- Looking for mmap
-- Looking for mmap - found
-- Looking for isatty
-- Looking for isatty - found
-- Looking for unistd.h
-- Looking for unistd.h - found
-- Looking for sys/mman.h
-- Looking for sys/mman.h - found
-- Looking for stdbool.h
-- Looking for stdbool.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Check if compiler accepts -pthread
-- Check if compiler accepts -pthread - yes
-- Found Threads: TRUE  
-- Found Freetype: ../installed/freetype/lib/libfreetype.a (found version "2.13.2") 
-- Looking for FT_Get_Var_Blend_Coordinates
-- Looking for FT_Get_Var_Blend_Coordinates - found
-- Looking for FT_Set_Var_Blend_Coordinates
-- Looking for FT_Set_Var_Blend_Coordinates - found
-- Looking for FT_Done_MM_Var
-- Looking for FT_Done_MM_Var - found
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.28") 
-- Performing Test CXX_SUPPORTS_FLAG_BSYMB_FUNCS
-- Performing Test CXX_SUPPORTS_FLAG_BSYMB_FUNCS - Success
-- Performing Test COMPILER_SUPPORTS_CXX11
-- Performing Test COMPILER_SUPPORTS_CXX11 - Success
-- Configuring done (30.4s)
-- Generating done (0.1s)
-- Build files have been written to: ./__harfbuzz_build

Error 1

In file included from ./harfbuzz/src/hb-serialize.hh:36:0,
                 from ./harfbuzz/src/hb-subset.hh:36,
                 from ./harfbuzz/src/hb-open-type.hh:37,
                 from ./harfbuzz/src/hb-aat-ltag-table.hh:28,
                 from ./harfbuzz/src/hb-aat-layout.hh:33,
                 from ./harfbuzz/src/hb-aat-layout.cc:30,
                 from ./harfbuzz/src/harfbuzz.cc:1:
./harfbuzz/src/hb-map.hh:109:40: error: ‘is_trivially_constructible’ is not a member of ‘std’
     static constexpr bool is_trivial = std::is_trivially_constructible<K>::value &&
                                        ^
./harfbuzz/src/hb-map.hh:109:73: error: expected primary-expression before ‘>’ token
     static constexpr bool is_trivial = std::is_trivially_constructible<K>::value &&
                                                                         ^
./harfbuzz/src/hb-map.hh:109:74: error: ‘::value’ has not been declared
     static constexpr bool is_trivial = std::is_trivially_constructible<K>::value &&
                                                                          ^
./harfbuzz/src/hb-map.hh:111:12: error: ‘is_trivially_constructible’ is not a member of ‘std’
            std::is_trivially_constructible<V>::value &&
            ^
./harfbuzz/src/hb-map.hh:111:45: error: expected primary-expression before ‘>’ token
            std::is_trivially_constructible<V>::value &&
                                             ^
./harfbuzz/src/hb-map.hh:111:46: error: ‘::value’ has not been declared
            std::is_trivially_constructible<V>::value &&
                                              ^

This error is easier to solve - due to known compiler bugs ('gcc < 5' - missing type traits implementation, we need to use build-in functions instead) - we just need to use already used defines from here:

harfbuzz/src/hb-meta.hh

Lines 202 to 214 in b8121cc

	#if defined(__GNUC__) && __GNUC__ < 5 && !defined(__clang__)
	#define hb_is_trivially_copyable(T) __has_trivial_copy(T)
	#define hb_is_trivially_copy_assignable(T) __has_trivial_assign(T)
	#define hb_is_trivially_constructible(T) __has_trivial_constructor(T)
	#define hb_is_trivially_copy_constructible(T) __has_trivial_copy_constructor(T)
	#define hb_is_trivially_destructible(T) __has_trivial_destructor(T)
	#else
	#define hb_is_trivially_copyable(T) std::is_trivially_copyable<T>::value
	#define hb_is_trivially_copy_assignable(T) std::is_trivially_copy_assignable<T>::value
	#define hb_is_trivially_constructible(T) std::is_trivially_constructible<T>::value
	#define hb_is_trivially_copy_constructible(T) std::is_trivially_copy_constructible<T>::value
	#define hb_is_trivially_destructible(T) std::is_trivially_destructible<T>::value
	#endif

so

harfbuzz/src/hb-map.hh

Lines 109 to 112 in b8121cc

	static constexpr bool is_trivial = std::is_trivially_constructible<K>::value &&
	std::is_trivially_destructible<K>::value &&
	std::is_trivially_constructible<V>::value &&
	std::is_trivially_destructible<V>::value;

become

    static constexpr bool is_trivial = hb_is_trivially_constructible(K) &&
				       hb_is_trivially_destructible(K) &&
				       hb_is_trivially_constructible(V) &&
				       hb_is_trivially_destructible(V);

Error 2

In file included from ./harfbuzz/src/hb.hh:531:0,
                 from ./harfbuzz/src/hb-aat-layout.cc:28,
                 from ./harfbuzz/src/harfbuzz.cc:1:
./harfbuzz/src/hb-map.hh: In instantiation of ‘struct hb_hashmap_t<unsigned int, unsigned int, true>’:
./harfbuzz/src/hb-map.hh:525:19:   required from here
./harfbuzz/src/hb-map.hh:401:29: error: cannot call member function ‘unsigned int hb_hashmap_t<K, V, minus_one>::size() const [with K = unsigned int; V = unsigned int; bool minus_one = true]’ without object
     + hb_iter (items, size ())
                             ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:406:19: error: ‘iter_items’ was not declared in this scope
     + iter_items ()
                   ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:411:19: error: ‘iter_items’ was not declared in this scope
     + iter_items ()
                   ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:416:19: error: ‘iter_items’ was not declared in this scope
     + iter_items ()
                   ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:421:17: error: ‘keys_ref’ was not declared in this scope
     + keys_ref ()
                 ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:426:19: error: ‘iter_items’ was not declared in this scope
     + iter_items ()
                   ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^
./harfbuzz/src/hb-map.hh:431:19: error: ‘values_ref’ was not declared in this scope
     + values_ref ()
                   ^
./harfbuzz/src/hb-meta.hh:76:41: note: in definition of macro ‘HB_AUTO_RETURN’
 #define HB_AUTO_RETURN(E) -> decltype ((E)) { return (E); }
                                         ^

This is the first time I have encountered errors of this kind, but a quick search suggested that here we need to add an explicit
this-> in related places:

• https://stackoverflow.com/questions/5147492/member-function-call-in-decltype
• https://stackoverflow.com/questions/20312062/cannot-call-member-function-without-object-inside-unevaluated-context-gc

So the next code:

harfbuzz/src/hb-map.hh

Lines 399 to 433 in b8121cc

	auto iter_items () const HB_AUTO_RETURN
	(
	+ hb_iter (items, size ())
	| hb_filter (&item_t::is_real)
	)
	auto iter_ref () const HB_AUTO_RETURN
	(
	+ iter_items ()
	| hb_map (&item_t::get_pair_ref)
	)
	auto iter () const HB_AUTO_RETURN
	(
	+ iter_items ()
	| hb_map (&item_t::get_pair)
	)
	auto keys_ref () const HB_AUTO_RETURN
	(
	+ iter_items ()
	| hb_map (&item_t::get_key)
	)
	auto keys () const HB_AUTO_RETURN
	(
	+ keys_ref ()
	| hb_map (hb_ridentity)
	)
	auto values_ref () const HB_AUTO_RETURN
	(
	+ iter_items ()
	| hb_map (&item_t::get_value)
	)
	auto values () const HB_AUTO_RETURN
	(
	+ values_ref ()
	| hb_map (hb_ridentity)
	)

become a little bit explicit:

  auto iter_items () const HB_AUTO_RETURN
  (
    + hb_iter (items, this->size ())
    | hb_filter (&item_t::is_real)
  )
  auto iter_ref () const HB_AUTO_RETURN
  (
    + this->iter_items ()
    | hb_map (&item_t::get_pair_ref)
  )
  auto iter () const HB_AUTO_RETURN
  (
    + this->iter_items ()
    | hb_map (&item_t::get_pair)
  )
  auto keys_ref () const HB_AUTO_RETURN
  (
    + this->iter_items ()
    | hb_map (&item_t::get_key)
  )
  auto keys () const HB_AUTO_RETURN
  (
    + this->keys_ref ()
    | hb_map (hb_ridentity)
  )
  auto values_ref () const HB_AUTO_RETURN
  (
    + this->iter_items ()
    | hb_map (&item_t::get_value)
  )
  auto values () const HB_AUTO_RETURN
  (
    + this->values_ref ()
    | hb_map (hb_ridentity)
  )

Error 3

In file included from ./harfbuzz/src/hb.hh:540:0,
                 from ./harfbuzz/src/hb-aat-layout.cc:28,
                 from ./harfbuzz/src/harfbuzz.cc:1:
./harfbuzz/src/hb-vector.hh: In instantiation of ‘Type hb_vector_t<Type, sorted>::pop() [with Type = hb_user_data_array_t::hb_user_data_item_t; bool sorted = false]’:
./harfbuzz/src/hb-object.hh:127:7:   required from ‘void hb_lockable_set_t<item_t, lock_t>::fini(lock_t&) [with item_t = hb_user_data_array_t::hb_user_data_item_t; lock_t = hb_mutex_t]’
./harfbuzz/src/hb-object.hh:178:34:   required from here
./harfbuzz/src/hb-vector.hh:463:43: error: cannot convert ‘std::remove_reference<hb_user_data_array_t::hb_user_data_item_t&>::type {aka hb_user_data_array_t::hb_user_data_item_t}’ to ‘hb_user_data_key_t*’ in initialization
     Type v {std::move (arrayZ[length - 1])};
                                           ^

The strangest mistake that took a lot of time. As can be seen from the strange error message, the compiler does not understand what we want at all. Let's look at the relevant code blocks:

harfbuzz/src/hb-object.hh

Lines 160 to 174 in b8121cc

	struct hb_user_data_array_t
	{
	struct hb_user_data_item_t {
	hb_user_data_key_t *key;
	void *data;
	hb_destroy_func_t destroy;
	bool operator == (const hb_user_data_key_t *other_key) const { return key == other_key; }
	bool operator == (const hb_user_data_item_t &other) const { return key == other.key; }
	void fini () { if (destroy) destroy (data); }
	};
	hb_mutex_t lock;
	hb_lockable_set_t<hb_user_data_item_t, hb_mutex_t> items;

harfbuzz/src/hb-vector.hh

Lines 460 to 467 in b8121cc

	Type pop ()
	{
	if (!length) return Null (Type);
	Type v {std::move (arrayZ[length - 1])};
	arrayZ[length - 1].~Type ();
	length--;
	return v;
	}

The simplest explanation I came up with for this error is: weak support of 'list initialization' (using curly braces) in old compiler. So to solve it I simply replaced 'curly braces' with 'parentheses':

Type v {std::move (arrayZ[length - 1])};
//     ^                              ^

become

Type v (std::move (arrayZ[length - 1]));
//     ^                              ^

and it fixes it! :D

---

The subsequent build was successful - without errors, although with a few warnings, in the style:

./harfbuzz/src/hb-ot-map.cc:90:44: warning: cannot optimize loop, the loop counter may overflow [-Wunsafe-loop-optimizations]
 hb_ot_map_builder_t::~hb_ot_map_builder_t ()
                                            ^

./harfbuzz/src/hb-serialize.hh:193:5: warning: cannot optimize loop, the loop counter may overflow [-Wunsafe-loop-optimizations]
     for (object_t *_ : ++hb_iter (packed)) _->fini ();
     ^

./harfbuzz/src/hb-ot-layout.cc: In function ‘hb_bool_t hb_ot_layout_get_font_extents(hb_font_t*, hb_direction_t, hb_tag_t, hb_tag_t, hb_font_extents_t*)’:
./harfbuzz/src/hb-ot-layout.cc:2131:31: warning: ‘max’ may be used uninitialized in this function [-Wmaybe-uninitialized]
       extents->ascender  = max;
                               ^
./harfbuzz/src/hb-ot-layout.cc:2132:31: warning: ‘min’ may be used uninitialized in this function [-Wmaybe-uninitialized]
       extents->descender = min;
                               ^

Unfortunately, github does not allow to paste the entire build log here. For those interested, you can watch it here.

I really appreciate the support of legacy systems in our imprefect world. I hope this pull request will be considered with understanding. Thanks for your time!

[behdad]

Thank you for debugging this and submitting fixes. Typically people just throw the errors in an issue and then I have to scratch my head about how to fix. :)