Support compiling for earlier releases of macOS (#960)

CMakeLists.txt

@@ -233,7 +233,7 @@ elseif(APPLE)
             src/platform/macos/display.mm
             src/platform/macos/input.cpp
             src/platform/macos/microphone.mm
-            src/platform/macos/misc.cpp
+            src/platform/macos/misc.mm
             src/platform/macos/misc.h
             src/platform/macos/nv12_zero_device.cpp
             src/platform/macos/nv12_zero_device.h
@@ -620,6 +620,8 @@ endif()
 
 if(APPLE)
     target_link_options(sunshine PRIVATE LINKER:-sectcreate,__TEXT,__info_plist,${APPLE_PLIST_FILE})
+    # Tell linker to dynamically load these symbols at runtime, in case they're unavailable:
+    target_link_options(sunshine PRIVATE -Wl,-U,_CGPreflightScreenCaptureAccess -Wl,-U,_CGRequestScreenCaptureAccess)
 endif()
 
 foreach(flag IN LISTS SUNSHINE_COMPILE_OPTIONS)

src/platform/macos/av_audio.m

@@ -3,11 +3,32 @@
 @implementation AVAudio
 
 + (NSArray<AVCaptureDevice *> *)microphones {
-  AVCaptureDeviceDiscoverySession *discoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInMicrophone,
-    AVCaptureDeviceTypeExternalUnknown]
-                                                                                                             mediaType:AVMediaTypeAudio
-                                                                                                              position:AVCaptureDevicePositionUnspecified];
-  return discoverySession.devices;
+
+  if([[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:((NSOperatingSystemVersion) { 10, 15, 0 })]) {
+    // This will generate a warning about AVCaptureDeviceDiscoverySession being
+    // unavailable before macOS 10.15, but we have a guard to prevent it from
+    // being called on those earlier systems.
+    // Unfortunately the supported way to silence this warning, using @available,
+    // produces linker errors for __isPlatformVersionAtLeast, so we have to use
+    // a different method.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunguarded-availability-new"
+    AVCaptureDeviceDiscoverySession *discoverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInMicrophone,
+      AVCaptureDeviceTypeExternalUnknown]
+                                                                                                               mediaType:AVMediaTypeAudio
+                                                                                                                position:AVCaptureDevicePositionUnspecified];
+    return discoverySession.devices;
+#pragma clang diagnostic pop
+  }
+  else {
+    // We're intentionally using a deprecated API here specifically for versions
+    // of macOS where it's not deprecated, so we can ignore any deprecation
+    // warnings:
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+    return [AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio];
+#pragma clang diagnostic pop
+  }
 }
 
 + (NSArray<NSString *> *)microphoneNames {

src/platform/macos/misc.mm

@@ -1,3 +1,4 @@
+#include <Foundation/Foundation.h>
 #include <arpa/inet.h>
 #include <dlfcn.h>
 #include <fcntl.h>
@@ -17,13 +18,40 @@ namespace bp = boost::process;
 
 namespace platf {
 
+// Even though the following two functions are available starting in macOS 10.15, they weren't
+// actually in the Mac SDK until Xcode 12.2, the first to include the SDK for macOS 11
+#if __MAC_OS_X_VERSION_MAX_ALLOWED < 110000 // __MAC_11_0
+// If they're not in the SDK then we can use our own function definitions.
+// Need to use weak import so that this will link in macOS 10.14 and earlier
+extern "C" bool CGPreflightScreenCaptureAccess(void) __attribute__((weak_import));
+extern "C" bool CGRequestScreenCaptureAccess(void) __attribute__((weak_import));
+#endif
+
 std::unique_ptr<deinit_t> init() {
-  if(!CGPreflightScreenCaptureAccess()) {
+  // This will generate a warning about CGPreflightScreenCaptureAccess and
+  // CGRequestScreenCaptureAccess being unavailable before macOS 10.15, but
+  // we have a guard to prevent it from being called on those earlier systems.
+  // Unfortunately the supported way to silence this warning, using @available,
+  // produces linker errors for __isPlatformVersionAtLeast, so we have to use
+  // a different method.
+  // We also ignore "tautological-pointer-compare" because when compiling with
+  // Xcode 12.2 and later, these functions are not weakly linked and will never
+  // be null, and therefore generate this warning. Since we are weakly linking
+  // when compiling with earlier Xcode versions, the check for null is
+  // necessary and so we ignore the warning.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunguarded-availability-new"
+#pragma clang diagnostic ignored "-Wtautological-pointer-compare"
+  if([[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:((NSOperatingSystemVersion) { 10, 15, 0 })] &&
+     // Double check that these weakly-linked symbols have been loaded:
+     CGPreflightScreenCaptureAccess != nullptr && CGRequestScreenCaptureAccess != nullptr &&
+     !CGPreflightScreenCaptureAccess()) {
     BOOST_LOG(error) << "No screen capture permission!"sv;
     BOOST_LOG(error) << "Please activate it in 'System Preferences' -> 'Privacy' -> 'Screen Recording'"sv;
     CGRequestScreenCaptureAccess();
     return nullptr;
   }
+#pragma clang diagnostic pop
   return std::make_unique<deinit_t>();
 }