Fix crash when reloading section that gets deleted

Summary: Rare, but very real crash that occurs when a reload is manually queued and then the section gets deleted in a diff.

Reviewed By: jeremycohen

Differential Revision: D4267678

fbshipit-source-id: a5bedf77934ff85f76830e3f0123a993fc5d885c

CHANGELOG.md

@@ -94,6 +94,8 @@ This release closes the [2.0.0 milestone](https://github.com/Instagram/IGListKit
 
 - Skip reloading for objects that are not found when calling `-[IGListAdapter reloadObjects:]`. [Ryan Nystrom](https://github.com/rnystrom) (tbd)
 
+- Fixes a crash when a reload is queued for an object that is deleted in the same runloop turn. [Ryan Nystrom](https://github.com/rnystrom) (tbd)
+
 ### Documentation
 
 - We now have 100% documentation coverage. Docs been refined and clarified. [Jesse Squires](https://github.com/jessesquires) [(#207)](https://github.com/Instagram/IGListKit/pull/207)

Source/IGListAdapterUpdater.m

@@ -234,8 +234,16 @@ void convertReloadToDeleteInsert(NSMutableIndexSet *reloads,
         const NSUInteger from = hasObjects ? [result oldIndexForIdentifier:diffIdentifier] : idx;
         const NSUInteger to = hasObjects ? [result newIndexForIdentifier:diffIdentifier] : idx;
         [reloads removeIndex:from];
-        [deletes addIndex:from];
-        [inserts addIndex:to];
+
+        // if a reload is queued outside the diff and the object was inserted or deleted it cannot be
+        if (from != NSNotFound && to != NSNotFound) {
+            [deletes addIndex:from];
+            [inserts addIndex:to];
+        } else {
+            IGAssert([result.deletes containsIndex:idx],
+                     @"Reloaded section %zi was not found in deletes with from: %zi, to: %zi, deletes: %@",
+                     idx, from, to, deletes);
+        }
     }];
 }
 

Tests/IGListAdapterUpdaterTests.m

@@ -384,4 +384,17 @@ - (void)test_whenConvertingReloads_withChanges_thatIndexMoves {
     XCTAssertTrue([inserts containsIndex:0]);
 }
 
+- (void)test_whenReloadingSection_whenSectionRemoved_thatConvertMethodCorrects {
+    NSArray *from = @[@"a", @"b", @"c"];
+    NSArray *to = @[@"a", @"c"];
+    IGListIndexSetResult *result = IGListDiff(from, to, IGListDiffEquality);
+    NSMutableIndexSet *reloads = [NSMutableIndexSet indexSetWithIndex:1];
+    NSMutableIndexSet *deletes = [NSMutableIndexSet new];
+    NSMutableIndexSet *inserts = [NSMutableIndexSet new];
+    convertReloadToDeleteInsert(reloads, deletes, inserts, result, from);
+    XCTAssertEqual(reloads.count, 0);
+    XCTAssertEqual(deletes.count, 0);
+    XCTAssertEqual(inserts.count, 0);
+}
+
 @end