Bug 1321321 - Ensure that we always save files with the given extension / Work-around NSSavePanel limitations when saving files with multiple extensions. r=mstange.

widget/cocoa/nsFilePicker.mm

@@ -458,23 +458,38 @@ nsFilePicker::PutLocalFile(const nsString& inTitle, const nsString& inDefaultNam
   // set up default file name
   NSString* defaultFilename = [NSString stringWithCharacters:(const unichar*)inDefaultName.get() length:inDefaultName.Length()];
 
-  // set up allowed types; this prevents the extension from being selected
-  // use the UTI for the file type to allow alternate extensions (e.g., jpg vs. jpeg)
+  // Set up the allowed type. This prevents the extension from being selected.
   NSString* extension = defaultFilename.pathExtension;
   if (extension.length != 0) {
-    CFStringRef type = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (CFStringRef)extension, NULL);
-
-    if (type) {
-      thePanel.allowedFileTypes = @[(NSString*)type];
-      CFRelease(type);
-    } else {
-      // if there's no UTI for the file extension, use the extension itself.
-      thePanel.allowedFileTypes = @[extension];
-    }
+    thePanel.allowedFileTypes = @[extension];
   }
   // Allow users to change the extension.
   thePanel.allowsOtherFileTypes = YES;
 
+  // If extensions are hidden and we’re saving a file with multiple extensions,
+  // only the last extension will be hidden in the panel (".tar.gz" will become
+  // ".tar"). If the remaining extension is known, the OS will think that we're
+  // trying to add a non-default extension. To avoid the confusion, we ensure
+  // that all extensions are shown in the panel if the remaining extension is
+  // known by the OS.
+  NSString* fileName =
+    [[defaultFilename lastPathComponent] stringByDeletingPathExtension];
+  NSString* otherExtension = fileName.pathExtension;
+  if (otherExtension.length != 0) {
+    // There's another extension here. Get the UTI.
+    CFStringRef type =
+      UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension,
+                                            (CFStringRef)otherExtension, NULL);
+    if (type) {
+      if (!CFStringHasPrefix(type, CFSTR("dyn."))) {
+        // We have a UTI, otherwise the type would have a "dyn." prefix. Ensure
+        // extensions are shown in the panel.
+        [thePanel setExtensionHidden:NO];
+      }
+      CFRelease(type);
+    }
+  }
+
   // set up default directory
   NSString *theDir = PanelDefaultDirectory();
   if (theDir) {