Cocoa: Add fully dynamic loading of Vulkan loader

If the application is not linked against the Vulkan loader and relies on
a third-party loader library or glfwGetInstanceProcAddress, then our
call to dlopen will fail without a custom dyld environment variable.

This adds a fallback of looking in the directory of the main executable,
which matches the bundle structure recommended by the Vulkan SDK, making
that finally work out of the box for fully dynamic loading.

README.md

@@ -142,6 +142,7 @@ information on what to include when reporting a bug.
    window (#1499)
  - [Win32] Bugfix: Disabled cursor mode interfered with some non-client actions
  - [Cocoa] Added support for `VK_EXT_metal_surface` (#1619)
+ - [Cocoa] Added locating the Vulkan loader at runtime in an application bundle
  - [Cocoa] Removed dependency on the CoreVideo framework
  - [Cocoa] Bugfix: `glfwSetWindowSize` used a bottom-left anchor point (#1553)
  - [Cocoa] Bugfix: Window remained on screen after destruction until event poll

src/cocoa_init.m

@@ -463,6 +463,32 @@ - (void)applicationDidHide:(NSNotification *)notification
 @end // GLFWApplicationDelegate
 
 
+//////////////////////////////////////////////////////////////////////////
+//////                       GLFW internal API                      //////
+//////////////////////////////////////////////////////////////////////////
+
+void* _glfwLoadLocalVulkanLoaderNS(void)
+{
+    CFBundleRef bundle = CFBundleGetMainBundle();
+    if (!bundle)
+        return NULL;
+
+    CFURLRef url =
+        CFBundleCopyAuxiliaryExecutableURL(bundle, CFSTR("libvulkan.1.dylib"));
+    if (!url)
+        return NULL;
+
+    char path[PATH_MAX];
+    void* handle = NULL;
+
+    if (CFURLGetFileSystemRepresentation(url, true, (UInt8*) path, sizeof(path) - 1))
+        handle = _glfw_dlopen(path);
+
+    CFRelease(url);
+    return handle;
+}
+
+
 //////////////////////////////////////////////////////////////////////////
 //////                       GLFW platform API                      //////
 //////////////////////////////////////////////////////////////////////////

src/cocoa_platform.h

@@ -207,3 +207,5 @@ void _glfwRestoreVideoModeNS(_GLFWmonitor* monitor);
 
 float _glfwTransformYNS(float y);
 
+void* _glfwLoadLocalVulkanLoaderNS(void);
+

src/vulkan.c

@@ -57,6 +57,8 @@ GLFWbool _glfwInitVulkan(int mode)
     _glfw.vk.handle = _glfw_dlopen("vulkan-1.dll");
 #elif defined(_GLFW_COCOA)
     _glfw.vk.handle = _glfw_dlopen("libvulkan.1.dylib");
+    if (!_glfw.vk.handle)
+        _glfw.vk.handle = _glfwLoadLocalVulkanLoaderNS();
 #else
     _glfw.vk.handle = _glfw_dlopen("libvulkan.so.1");
 #endif