From 71a4f800b1d7d214fa223705d70440a7edccaebf Mon Sep 17 00:00:00 2001
From: Lukas Renggli <renggli@gmail.com>
Date: Sun, 3 Sep 2023 18:07:08 +0200
Subject: [PATCH] When growing a BitList make sure all newly exposed values are
 properly initialized.

---
 lib/src/collection/bitlist.dart | 48 +++++++++++++++++++--------------
 test/collection_test.dart       | 17 ++++++++++++
 2 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/lib/src/collection/bitlist.dart b/lib/src/collection/bitlist.dart
index 27f71c0..e720642 100644
--- a/lib/src/collection/bitlist.dart
+++ b/lib/src/collection/bitlist.dart
@@ -107,26 +107,7 @@ abstract class BitList extends ListBase<bool> {
   @override
   void fillRange(int start, int end, [bool? fill]) {
     RangeError.checkValidRange(start, end, length);
-    if (start == end) return;
-    final startIndex = start >> bitShift, startBit = start & bitOffset;
-    final endIndex = (end - 1) >> bitShift, endBit = (end - 1) & bitOffset;
-    if (startIndex == endIndex) {
-      if (fill == true) {
-        buffer[startIndex] |= ((1 << (endBit - startBit + 1)) - 1) << startBit;
-      } else {
-        buffer[startIndex] &= ((1 << startBit) - 1) | (bitMask << (endBit + 1));
-      }
-    } else {
-      if (fill == true) {
-        buffer[startIndex] |= bitMask << startBit;
-        buffer.fillRange(startIndex + 1, endIndex, bitMask);
-        buffer[endIndex] |= (1 << (endBit + 1)) - 1;
-      } else {
-        buffer[startIndex] &= (1 << startBit) - 1;
-        buffer.fillRange(startIndex + 1, endIndex, 0);
-        buffer[endIndex] &= bitMask << (endBit + 1);
-      }
-    }
+    _fillRange(buffer, start, end, fill ?? false);
   }
 
   /// Sets the bit at the specified [index] to the complement of its current
@@ -332,6 +313,10 @@ class GrowableBitList extends BitList {
       newBuffer.setRange(0, newBuffer.length, buffer);
       buffer = newBuffer;
     }
+    if (_length < length) {
+      // When growing, make sure we always have predictable state.
+      _fillRange(buffer, _length, length, false);
+    }
     _length = length;
   }
 }
@@ -425,3 +410,26 @@ const List<int> bitClearMask = [
   -1073741825,
   -2147483649
 ];
+
+void _fillRange(Uint32List buffer, int start, int end, bool? fill) {
+  if (start == end) return;
+  final startIndex = start >> bitShift, startBit = start & bitOffset;
+  final endIndex = (end - 1) >> bitShift, endBit = (end - 1) & bitOffset;
+  if (startIndex == endIndex) {
+    if (fill == true) {
+      buffer[startIndex] |= ((1 << (endBit - startBit + 1)) - 1) << startBit;
+    } else {
+      buffer[startIndex] &= ((1 << startBit) - 1) | (bitMask << (endBit + 1));
+    }
+  } else {
+    if (fill == true) {
+      buffer[startIndex] |= bitMask << startBit;
+      buffer.fillRange(startIndex + 1, endIndex, bitMask);
+      buffer[endIndex] |= (1 << (endBit + 1)) - 1;
+    } else {
+      buffer[startIndex] &= (1 << startBit) - 1;
+      buffer.fillRange(startIndex + 1, endIndex, 0);
+      buffer[endIndex] &= bitMask << (endBit + 1);
+    }
+  }
+}
diff --git a/test/collection_test.dart b/test/collection_test.dart
index f422655..e512e0f 100644
--- a/test/collection_test.dart
+++ b/test/collection_test.dart
@@ -607,6 +607,23 @@ void main() {
             target.length -= 2;
             expect(target.buffer, same(buffer));
           });
+          test('length (cleared)', () {
+            final generator = Random(584);
+            for (var i = 0; i < 0xff; i++) {
+              final original = 1 + generator.nextInt(0xff);
+              final smaller = generator.nextInt(original);
+              final larger = original + generator.nextInt(0xff);
+              final target = BitList.filled(original, true, growable: growable);
+              target.length = smaller;
+              target.length = larger;
+              for (var i = 0; i < smaller; i++) {
+                expect(target[i], isTrue);
+              }
+              for (var i = smaller; i < larger; i++) {
+                expect(target[i], isFalse);
+              }
+            }
+          });
           test('removeLast', () {
             final source = randomBooleans(453, 500);
             final target = BitList.of(source, growable: growable);