[iOS] Adding -ListMode.collapsableMode

Adding collapsableMode property in ListMode which can have 2 values:
 + ListModelCollapsableModeHeader
 + ListModelCollapsableModeFirstCell

The header mode is used to when the header to collapse a section. When
collapsed, a section contains no item.

The first cell mode is used to when the first cell to collapse a
section. When collapsed, a section contains the first item.


Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: If46f85d5c412b1b799099635fefe7a8c8d11bbf2
Reviewed-on: https://chromium-review.googlesource.com/1101558
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568495}

ios/chrome/browser/ui/list_model/list_model.h

@@ -9,6 +9,15 @@
 
 @class ListItem;
 
+// Collapsable mode to use either the header cell or the first cell to collapse
+// sections in ListMode.
+typedef NS_ENUM(NSInteger, ListModelCollapsableMode) {
+  // When a section is collapsed, all items are hidden.
+  ListModelCollapsableModeHeader = 0,
+  // When a section is collapsed, all items except the first one are hidden.
+  ListModelCollapsableModeFirstCell,
+};
+
 // Key for saving collapsed state in the NSUserDefaults.
 extern NSString* const kListModelCollapsedKey;
 
@@ -189,6 +198,9 @@ const NSInteger kItemTypeEnumZero = 100;
 
 #pragma mark Collapsing methods.
 
+// The default value is ListModelCollapsableModeHeader.
+@property(nonatomic, assign) ListModelCollapsableMode collapsableMode;
+
 // Sets an existing |sectionIdentifier| |collapsedKey| to be used when
 // collapsing or expanding a section. |collapsedKey| is a unique identifier for
 // each section that will be used for persisting information about the collapsed

ios/chrome/browser/ui/list_model/list_model.mm

@@ -34,6 +34,8 @@ typedef NSMutableArray<ListItem*> SectionItems;
   NSMutableDictionary<NSNumber*, NSString*>* _collapsedKeys;
 }
 
+@synthesize collapsableMode = _collapsableMode;
+
 - (instancetype)init {
   if ((self = [super init])) {
     _sectionIdentifiers = [[NSMutableArray alloc] init];
@@ -293,9 +295,17 @@ typedef NSMutableArray<ListItem*> SectionItems;
 - (NSInteger)numberOfItemsInSection:(NSInteger)section {
   DCHECK_LT(base::checked_cast<NSUInteger>(section), [_sections count]);
   NSInteger sectionIdentifier = [self sectionIdentifierForSection:section];
-  if ([self sectionIsCollapsed:sectionIdentifier])
-    return 0;
   SectionItems* items = [_sections objectAtIndex:section];
+  if ([self sectionIsCollapsed:sectionIdentifier]) {
+    switch (self.collapsableMode) {
+      case ListModelCollapsableModeHeader:
+        return 0;
+      case ListModelCollapsableModeFirstCell:
+        DCHECK_LT(0ul, items.count);
+        return 1;
+    }
+    NOTREACHED();
+  }
   return items.count;
 }
 

ios/chrome/browser/ui/list_model/list_model_collapse_unittest.mm

@@ -174,4 +174,27 @@ TEST_F(ListModelCollapseTest, PersistCollapsedSections) {
   EXPECT_TRUE([model sectionIsCollapsed:SectionIdentifierBar]);
 }
 
+TEST_F(ListModelCollapseTest, CollapsedSectionMode) {
+  model.collapsableMode = ListModelCollapsableModeFirstCell;
+  [model setSection:SectionIdentifierFoo collapsed:YES];
+  [model setSection:SectionIdentifierBar collapsed:YES];
+
+  // SectionIdentifierFoo
+  EXPECT_EQ(1, [model numberOfItemsInSection:0]);
+  EXPECT_TRUE([model sectionIsCollapsed:SectionIdentifierFoo]);
+  // SectionIdentifierBar
+  EXPECT_EQ(1, [model numberOfItemsInSection:1]);
+  EXPECT_TRUE([model sectionIsCollapsed:SectionIdentifierBar]);
+
+  [model setSection:SectionIdentifierFoo collapsed:NO];
+  [model setSection:SectionIdentifierBar collapsed:NO];
+
+  // SectionIdentifierFoo
+  EXPECT_EQ(1, [model numberOfItemsInSection:0]);
+  EXPECT_FALSE([model sectionIsCollapsed:SectionIdentifierFoo]);
+  // SectionIdentifierBar
+  EXPECT_EQ(2, [model numberOfItemsInSection:1]);
+  EXPECT_FALSE([model sectionIsCollapsed:SectionIdentifierBar]);
+}
+
 }  // namespace