Add -Wl,-dead_strip_dylibs support

* `-Wl,-dead_strip_dylibs` is the analogue
  of `-Wl,--as-needed` on macOS.

mesonbuild/compilers/compilers.py

@@ -348,7 +348,7 @@ def get_base_link_args(options, linker, is_shared_module):
         pass
     try:
         if 'b_asneeded' in linker.base_options and options['b_asneeded'].value:
-            args.append('-Wl,--as-needed')
+            args.append(linker.get_asneeded_args())
     except KeyError:
         pass
     try:
@@ -900,6 +900,13 @@ ICC_STANDARD = 0
 ICC_OSX = 1
 ICC_WIN = 2
 
+# GNU ld cannot be installed on macOS
+# https://github.com/Homebrew/homebrew-core/issues/17794#issuecomment-328174395
+# Hence, we don't need to differentiate between OS and ld
+# for the sake of adding as-needed support
+GNU_LD_AS_NEEDED = '-Wl,--as-needed'
+APPLE_LD_AS_NEEDED = '-Wl,-dead_strip_dylibs'
+
 def get_gcc_soname_args(gcc_type, prefix, shlib_name, suffix, path, soversion, is_shared_module):
     if soversion is None:
         sostr = ''
@@ -1002,10 +1009,18 @@ class GnuCompiler:
                              'b_colorout', 'b_ndebug', 'b_staticpic']
         if self.gcc_type != GCC_OSX:
             self.base_options.append('b_lundef')
-            self.base_options.append('b_asneeded')
+        self.base_options.append('b_asneeded')
         # All GCC backends can do assembly
         self.can_compile_suffixes.add('s')
 
+    # TODO: centralise this policy more globally, instead
+    # of fragmenting it into GnuCompiler and ClangCompiler
+    def get_asneeded_args(self):
+        if self.gcc_type == GCC_OSX:
+            return APPLE_LD_AS_NEEDED
+        else:
+            return GNU_LD_AS_NEEDED
+
     def get_colorout_args(self, colortype):
         if mesonlib.version_compare(self.version, '>=4.9.0'):
             return gnu_color_args[colortype][:]
@@ -1084,10 +1099,18 @@ class ClangCompiler:
                              'b_ndebug', 'b_staticpic', 'b_colorout']
         if self.clang_type != CLANG_OSX:
             self.base_options.append('b_lundef')
-            self.base_options.append('b_asneeded')
+        self.base_options.append('b_asneeded')
         # All Clang backends can do assembly and LLVM IR
         self.can_compile_suffixes.update(['ll', 's'])
 
+    # TODO: centralise this policy more globally, instead
+    # of fragmenting it into GnuCompiler and ClangCompiler
+    def get_asneeded_args(self):
+        if self.clang_type == CLANG_OSX:
+            return APPLE_LD_AS_NEEDED
+        else:
+            return GNU_LD_AS_NEEDED
+
     def get_pic_args(self):
         if self.clang_type in (CLANG_WIN, CLANG_OSX):
             return [] # On Window and OS X, pic is always on.

test cases/common/183 as-needed/config.h

@@ -0,0 +1,14 @@
+#if defined _WIN32 || defined __CYGWIN__
+  #if defined BUILDING_DLL
+    #define DLL_PUBLIC __declspec(dllexport)
+  #else
+    #define DLL_PUBLIC __declspec(dllimport)
+  #endif
+#else
+  #if defined __GNUC__
+    #define DLL_PUBLIC __attribute__ ((visibility("default")))
+  #else
+    #pragma message ("Compiler does not support symbol visibility.")
+    #define DLL_PUBLIC
+  #endif
+#endif

test cases/common/183 as-needed/libA.cpp

@@ -0,0 +1,7 @@
+#define BUILDING_DLL
+
+#include "libA.h"
+
+namespace meson_test_as_needed {
+  DLL_PUBLIC bool linked = false;
+}

test cases/common/183 as-needed/libA.h

@@ -0,0 +1,5 @@
+#include "config.h"
+
+namespace meson_test_as_needed {
+  DLL_PUBLIC extern bool linked;
+}

test cases/common/183 as-needed/libB.cpp

@@ -0,0 +1,19 @@
+#include "libA.h"
+
+#undef DLL_PUBLIC
+#define BUILDING_DLL
+#include "config.h"
+
+namespace meson_test_as_needed {
+  namespace {
+    bool set_linked() {
+      linked = true;
+      return true;
+    }
+    bool stub = set_linked();
+  }
+
+  DLL_PUBLIC int libB_unused_func() {
+    return 0;
+  }
+}

test cases/common/183 as-needed/main.cpp

@@ -0,0 +1,7 @@
+#include <cstdlib>
+
+#include "libA.h"
+
+int main() {
+  return (meson_test_as_needed::linked == false ? EXIT_SUCCESS : EXIT_FAILURE);
+}

test cases/common/183 as-needed/meson.build

@@ -0,0 +1,13 @@
+project('as-needed test', 'cpp')
+
+# Idea behind this test is to have -Wl,--as-needed prune
+# away unneeded linkages, which would otherwise cause global
+# static initialiser side-effects to set a boolean to true.
+
+# Credits for portable ISO C++ idea go to sarum9in
+
+libA = library('A', 'libA.cpp')
+libB = library('B', 'libB.cpp', link_with : libA)
+
+main_exe = executable('C', 'main.cpp', link_with : [libA, libB])
+test('main test', main_exe)