Fix: clear the display mark on a view with no area

Source/NSView.m

@@ -2601,6 +2601,16 @@ - (void) displayIfNeededInRectIgnoringOpacity: (NSRect)aRect
                       isect = [subview convertRect: isect fromView: self];
                       [subview displayIfNeededInRectIgnoringOpacity: isect];
                     }
+                  else if (NSIsEmptyRect(subviewFrame))
+                    {
+                      /* A subview with no area has nothing to draw, and is
+                         never reached by the line above, so it would keep
+                         itself and every view over it waiting for a display
+                         that cannot happen.  Let it settle its own flag.
+                      */
+                      [subview displayIfNeededInRectIgnoringOpacity:
+                        NSZeroRect];
+                    }
 
                   if (subview->_rFlags.needs_display)
                     {
@@ -2729,6 +2739,17 @@ - (void) displayRectIgnoringOpacity: (NSRect)aRect
                   [subview displayRectIgnoringOpacity: isect
                                             inContext: context];
                 }
+              else if (NSIsEmptyRect(subviewFrame)
+                && subview->_rFlags.needs_display == YES)
+                {
+                  /* A subview with no area has nothing to draw and is never
+                     reached by the line above, so it would keep itself and
+                     every view over it waiting for a display that cannot
+                     happen.  Let it settle its own flag.
+                  */
+                  [subview displayRectIgnoringOpacity: NSZeroRect
+                                            inContext: context];
+                }
               /*
                * Is there still something to draw in the subview?
                * This keeps the invariant that views further up are marked

Tests/gui/NSView/emptyViewNeedsDisplay.m

@@ -0,0 +1,101 @@
+/* A view with no area cannot draw anything.  Marking it for display and
+   then displaying the window has to leave it, and every view above it,
+   clear again; otherwise nothing in that branch of the tree ever reports
+   itself as drawn.  A view that has an area but falls outside the rectangle
+   being displayed is a different matter and keeps its mark.  Drawing needs
+   the backend, so the set is skipped without one.
+*/
+#include "Testing.h"
+
+#include <Foundation/NSAutoreleasePool.h>
+#include <Foundation/NSGeometry.h>
+
+#include <AppKit/NSApplication.h>
+#include <AppKit/NSBox.h>
+#include <AppKit/NSView.h>
+#include <AppKit/NSWindow.h>
+
+int
+main(int argc, char **argv)
+{
+  NSWindow *window;
+  NSView *content;
+  NSView *flat;
+  NSView *aside;
+  NSBox *box;
+
+  START_SET("NSView empty view needs display")
+
+  NS_DURING
+    {
+      [NSApplication sharedApplication];
+    }
+  NS_HANDLER
+    {
+      if ([[localException name] isEqualToString: NSInternalInconsistencyException])
+        SKIP("It looks like GNUstep backend is not yet installed")
+    }
+  NS_ENDHANDLER
+
+  NS_DURING
+    {
+      window = AUTORELEASE([[NSWindow alloc]
+        initWithContentRect: NSMakeRect(0, 0, 200, 200)
+                  styleMask: NSWindowStyleMaskBorderless
+                    backing: NSBackingStoreBuffered
+                      defer: NO]);
+      content = [window contentView];
+
+      flat = AUTORELEASE([[NSView alloc]
+        initWithFrame: NSMakeRect(10, 10, 100, 0)]);
+      [content addSubview: flat];
+      [flat setNeedsDisplay: YES];
+      [window orderFront: nil];
+      [window display];
+
+      PASS([flat needsDisplay] == NO,
+           "a view with no area does not wait for a display");
+      PASS([content needsDisplay] == NO,
+           "the view holding it does not wait either");
+      PASS([window viewsNeedDisplay] == NO,
+           "the window has nothing left to display");
+
+      /* A box two pixels high gives its content view no room at all, which
+         is how this turns up in a real window. */
+      box = AUTORELEASE([[NSBox alloc]
+        initWithFrame: NSMakeRect(10, 100, 180, 2)]);
+      [box setTitlePosition: NSNoTitle];
+      [content addSubview: box];
+      [window display];
+
+      PASS([[box contentView] needsDisplay] == NO,
+           "the content view of a box too short for it is not left waiting");
+      PASS([box needsDisplay] == NO, "nor is the box");
+      PASS([content needsDisplay] == NO, "nor is the view holding the box");
+
+      /* A view with an area that the displayed rectangle does not reach
+         keeps its mark, since it still has something to draw. */
+      aside = AUTORELEASE([[NSView alloc]
+        initWithFrame: NSMakeRect(150, 150, 20, 20)]);
+      [content addSubview: aside];
+      [window display];
+      [aside setNeedsDisplay: YES];
+      [content displayIfNeededInRect: NSMakeRect(0, 0, 40, 40)];
+
+      PASS([aside needsDisplay] == YES,
+           "a view outside the rectangle being displayed still waits");
+    }
+  NS_HANDLER
+    {
+      if ([[localException name] isEqualToString: NSInternalInconsistencyException]
+        || [[localException name] isEqualToString: @"NSWindowServerCommunicationException"])
+        SKIP("No display available")
+      else
+        [localException raise];
+    }
+  NS_ENDHANDLER
+
+  END_SET("NSView empty view needs display")
+
+  return 0;
+}