Fix NSWindowStyleMaskTexturedBackground deprecation warning

Seems like the flag has been completely useless since macOS 11. We
previously kept it around despite its deprecation status because it
seems to make the title bar not show a black line, but since macOS 11 it
has been showing that anyway, so remove usage of it. Also, clean up misc
pre-Lion-era code and block them behind ifdef. Can remove those code in
future if we want to clean up.

Author: ychin

src/MacVim/MMVimView.m

@@ -192,6 +192,10 @@ - (BOOL)isOpaque
     return textView.defaultBackgroundColor.alphaComponent == 1;
 }
 
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7
+// The core logic should not be reachable in 10.7 or above and is deprecated code.
+// See documentation for showsResizeIndicator and placeScrollbars: comments.
+// As such, just ifdef out the whole thing as we no longer support 10.7.
 - (void)drawRect:(NSRect)rect
 {
     // On Leopard, we want to have a textured window background for nice
@@ -202,9 +206,6 @@ - (void)drawRect:(NSRect)rect
             || !([[self window] styleMask] & NSWindowStyleMaskTexturedBackground))
         return;
 
-    // This should not be reachable in 10.7 or above and is deprecated code.
-    // See documentation for showsResizeIndicator and placeScrollbars: comments.
-
 #if (MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7)
     int sw = [NSScroller scrollerWidthForControlSize:NSControlSizeRegular scrollerStyle:NSScrollerStyleLegacy];
 #else
@@ -243,6 +244,7 @@ - (void)drawRect:(NSRect)rect
         [path stroke];
     }
 }
+#endif
 
 - (MMTextView *)textView
 {

src/MacVim/MMWindowController.m

@@ -128,10 +128,27 @@ - (id)initWithVimController:(MMVimController *)controller
 {
     backgroundDark = NO;
 
-    unsigned styleMask = NSWindowStyleMaskTitled | NSWindowStyleMaskClosable
-            | NSWindowStyleMaskMiniaturizable | NSWindowStyleMaskResizable
-            | NSWindowStyleMaskUnifiedTitleAndToolbar
-            | NSWindowStyleMaskTexturedBackground;
+    unsigned styleMask = NSWindowStyleMaskTitled
+                       | NSWindowStyleMaskClosable
+                       | NSWindowStyleMaskMiniaturizable
+                       | NSWindowStyleMaskResizable
+                       | NSWindowStyleMaskUnifiedTitleAndToolbar;
+
+    // Textured background has been a deprecated feature for a while. For a
+    // while we kept using it to avoid showing a black line below the title
+    // bar, but since macOS 11.0 this flag is completely ignored and
+    // deprecated. Since it's hard to test older versions of macOS well, simply
+    // preserve the existing functionality on older macOS versions, while not
+    // setting it in macOS 11+.
+    BOOL usingTexturedBackground = NO;
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_VERSION_11_0
+    if (@available(macos 11.0, *)) {
+        // Don't set the textured background because it's been completely deprecated and won't do anything.
+    } else {
+        styleMask = styleMask | NSWindowStyleMaskTexturedBackground;
+        usingTexturedBackground = YES;
+    }
+#endif
 
     NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
     if ([userDefaults boolForKey:MMNoTitleBarWindowKey]) {
@@ -179,7 +196,7 @@ - (id)initWithVimController:(MMVimController *)controller
     [win setDelegate:self];
     [win setInitialFirstResponder:[vimView textView]];
 
-    if ([win styleMask] & NSWindowStyleMaskTexturedBackground) {
+    if (usingTexturedBackground) {
         // On Leopard, we want to have a textured window to have nice
         // looking tabs. But the textured window look implies rounded
         // corners, which looks really weird -- disable them. This is a
@@ -1722,10 +1739,18 @@ - (void)updateTablineSeparator
 {
     BOOL tabBarVisible  = ![[vimView tabBarControl] isHidden];
     BOOL toolbarHidden  = [decoratedWindow toolbar] == nil;
-    BOOL windowTextured = ([decoratedWindow styleMask] &
-                            NSWindowStyleMaskTexturedBackground) != 0;
     BOOL hideSeparator  = NO;
 
+    // See initWithVimController: for textured background deprecation notes.
+    BOOL windowTextured = NO;
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_VERSION_11_0
+    if (@available(macos 11.0, *)) {
+    } else {
+        windowTextured = ([decoratedWindow styleMask] &
+                          NSWindowStyleMaskTexturedBackground) != 0;
+    }
+#endif
+
     if (floor(NSAppKitVersionNumber) >= NSAppKitVersionNumber10_10) {
         // The tabline separator is mostly an old feature and not necessary
         // modern macOS versions.