msglist: Suppress bottom inset in top sliver, too

Fixes #1523.

Chris reported the issue, debugged, and wrote the core of the fix.
I added the test, found that the left and right insets reappeared,
debugged why, and added removeLeft and removeRight to fix those.

Co-authored-by: Chris Bobbe <[email protected]>

Author: gnprice

lib/widgets/message_list.dart

@@ -1069,7 +1069,7 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
 
     // The top sliver has its child 0 as the item just before the
     // sliver boundary, child 1 as the item before that, and so on.
-    final topSliver = SliverStickyHeaderList(
+    Widget topSliver = SliverStickyHeaderList(
       headerPlacement: HeaderPlacement.scrollingStart,
       delegate: SliverChildBuilderDelegate(
         // To preserve state across rebuilds for individual [MessageItem]
@@ -1148,6 +1148,15 @@ class _MessageListState extends State<MessageList> with PerAccountStoreAwareStat
       // TODO(#311) If we have a bottom nav, it will pad the bottom inset,
       //   and this can be removed; also remove mention in MessageList dartdoc
       bottomSliver = SliverSafeArea(key: bottomSliver.key, sliver: bottomSliver);
+      topSliver = MediaQuery.removePadding(context: context,
+        // In the top sliver, forget the bottom inset;
+        // we're having the bottom sliver take care of it.
+        removeBottom: true,
+        // (Also forget the left and right insets; the outer SafeArea, above,
+        // does that, but the `context` we're passing to this `removePadding`
+        // is from outside that SafeArea, so we need to repeat it.)
+        removeLeft: true, removeRight: true,
+        child: topSliver);
     }
 
     return MessageListScrollView(

test/widgets/message_list_test.dart

@@ -405,7 +405,31 @@ void main() {
   });
 
   group('presents message content appropriately', () {
-    testWidgets('content not asked to consume insets (including bottom), even without compose box', (tester) async {
+    testWidgets('content not asked to consume insets (including bottom), even without compose box, in top sliver', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1523
+      const fakePadding = FakeViewPadding(left: 10, top: 10, right: 10, bottom: 10);
+      tester.view.viewInsets = fakePadding;
+      tester.view.padding = fakePadding;
+
+      await setupMessageListPage(tester, narrow: const CombinedFeedNarrow(),
+        messages: [
+          eg.streamMessage(content: ContentExample.codeBlockPlain.html),
+          eg.streamMessage(),
+        ]);
+
+      // Verify this message list lacks a compose box.
+      // (The original bug wouldn't reproduce with a compose box present.)
+      final state = MessageListPage.ancestorOf(tester.element(find.text("verb\natim")));
+      check(state.composeBoxState).isNull();
+      // Also verify that the first message is in the top sliver.
+      check(state.model!.middleMessage).equals(1);
+
+      final element = tester.element(find.byType(CodeBlock));
+      final padding = MediaQuery.of(element).padding;
+      check(padding).equals(EdgeInsets.zero);
+    });
+
+    testWidgets('content not asked to consume insets (including bottom), even without compose box, in bottom sliver', (tester) async {
       // Regression test for: https://github.com/zulip/zulip-flutter/issues/736
       const fakePadding = FakeViewPadding(left: 10, top: 10, right: 10, bottom: 10);
       tester.view.viewInsets = fakePadding;
@@ -418,6 +442,8 @@ void main() {
       // (The original bug wouldn't reproduce with a compose box present.)
       final state = MessageListPage.ancestorOf(tester.element(find.text("verb\natim")));
       check(state.composeBoxState).isNull();
+      // Also verify that the message is in the bottom sliver.
+      check(state.model!.middleMessage).equals(0);
 
       final element = tester.element(find.byType(CodeBlock));
       final padding = MediaQuery.of(element).padding;