Merge #16720: qt: Replace objc_msgSend() function calls with the native Objective-C syntax

0bb33b5348dbddd65b88a7f00449c965562355d3 qt: Replace objc_msgSend with native syntax (Hennadii Stepanov)

Pull request description:

  Changes in Xcode 11 Objective-C Runtime cause an error (#16387) during building on MacOS 10.15 Catalina.

  This PR fixes this issue by replacing `objc_msgSend()` function calls with the native Objective-C syntax.

  Refs:
  - [changes in `objc_msgSend` function](https://developer.apple.com/documentation/objectivec/1456712-objc_msgsend?changes=latest_minor&language=objc)
  - [`OBJC_OLD_DISPATCH_PROTOTYPES` macro](https://developer.apple.com/documentation/objectivec/objc_old_dispatch_prototypes?language=objc)

ACKs for top commit:
  l2a5b1:
    ACK 0bb33b5 - Diff looks good. Sending messages via native Objective-C code feels more robust and is more readable than casting all the `objc_msgSend` function calls to the appropriate function signature (which would also have fixed the issue).
  jonasschnelli:
    utACK 0bb33b5348dbddd65b88a7f00449c965562355d3 - Confirmed that the called macOS framework function is available on our build targets.
  fanquake:
    ACK 0bb33b5348dbddd65b88a7f00449c965562355d3 - Still works as expected.

Tree-SHA512: c09cb684d06bd1da053a17c182b7bb1642e45bb347d26c76e1c5d835c320567caee366d85e34bb7f2be38e63ed041e0d06a56c2a9d89f7e5bece9b19cc5c6772

3 files changed, 18 insertions, 13 deletions

diff --git a/configure.ac b/configure.ac
index 35bb0c0231..97974d0f14 100644
--- a/configure.ac
+++ b/configure.ac
@@ -585,7 +585,7 @@ case $host in
      fi
 
      AX_CHECK_LINK_FLAG([[-Wl,-headerpad_max_install_names]], [LDFLAGS="$LDFLAGS -Wl,-headerpad_max_install_names"])
-     CPPFLAGS="$CPPFLAGS -DMAC_OSX"
+     CPPFLAGS="$CPPFLAGS -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0"
      OBJCXXFLAGS="$CXXFLAGS"
      ;;
    *android*)
diff --git a/src/qt/guiutil.cpp b/src/qt/guiutil.cpp
index 59c7c0a44a..070df31aa6 100644
--- a/src/qt/guiutil.cpp
+++ b/src/qt/guiutil.cpp
@@ -57,9 +57,10 @@
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 
-#include <objc/objc-runtime.h>
 #include <CoreServices/CoreServices.h>
 #include <QProcess>
+
+void ForceActivation();
 #endif
 
 namespace GUIUtil {
@@ -359,10 +360,7 @@ bool isObscured(QWidget *w)
 void bringToFront(QWidget* w)
 {
 #ifdef Q_OS_MAC
-    // Force application activation on macOS. With Qt 5.4 this is required when
-    // an action in the dock menu is triggered.
-    id app = objc_msgSend((id) objc_getClass("NSApplication"), sel_registerName("sharedApplication"));
-    objc_msgSend(app, sel_registerName("activateIgnoringOtherApps:"), YES);
+    ForceActivation();
 #endif
 
     if (w) {
diff --git a/src/qt/macdockiconhandler.mm b/src/qt/macdockiconhandler.mm
index 102adce6c5..5eb23c76e6 100644
--- a/src/qt/macdockiconhandler.mm
+++ b/src/qt/macdockiconhandler.mm
@@ -1,12 +1,11 @@
-// Copyright (c) 2011-2018 The Bitcoin Core developers
+// Copyright (c) 2011-2019 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "macdockiconhandler.h"
 
-#undef slots
-#include <objc/objc.h>
-#include <objc/message.h>
+#include <AppKit/AppKit.h>
+#include <objc/runtime.h>
 
 static MacDockIconHandler *s_instance = nullptr;
 
@@ -21,9 +20,7 @@ bool dockClickHandler(id self, SEL _cmd, ...) {
 }
 
 void setupDockClickHandler() {
-    id app = objc_msgSend((id)objc_getClass("NSApplication"), sel_registerName("sharedApplication"));
-    id delegate = objc_msgSend(app, sel_registerName("delegate"));
-    Class delClass = (Class)objc_msgSend(delegate, sel_registerName("class"));
+    Class delClass = (Class)[[[NSApplication sharedApplication] delegate] class];
     SEL shouldHandle = sel_registerName("applicationShouldHandleReopen:hasVisibleWindows:");
     class_replaceMethod(delClass, shouldHandle, (IMP)dockClickHandler, "B@:");
 }
@@ -44,3 +41,13 @@ void MacDockIconHandler::cleanup()
 {
     delete s_instance;
 }
+
+/**
+ * Force application activation on macOS. With Qt 5.5.1 this is required when
+ * an action in the Dock menu is triggered.
+ * TODO: Define a Qt version where it's no-longer necessary.
+ */
+void ForceActivation()
+{
+    [[NSApplication sharedApplication] activateIgnoringOtherApps:YES];
+}