Enable unnecessary_null_checks lint (#82084)

analysis_options.yaml

@@ -204,7 +204,7 @@ linter:
     # - unnecessary_lambdas # has false positives: https://github.com/dart-lang/linter/issues/498
     - unnecessary_new
     - unnecessary_null_aware_assignments
-    # - unnecessary_null_checks # not yet tested
+    - unnecessary_null_checks
     - unnecessary_null_in_if_null_operators
     - unnecessary_nullable_for_final_variable_declarations
     - unnecessary_overrides

dev/snippets/lib/snippets.dart

@@ -227,7 +227,9 @@ class SnippetGenerator {
       if (match != null) { // If we saw the start or end of a code block
         inCodeBlock = !inCodeBlock;
         if (match.namedGroup('language') != null) {
-          language = match[1]!;
+          language = match[1];
+          assert(language != null);
+          language = language!;
           if (match.namedGroup('section') != null) {
             components.add(_ComponentTuple('code-${match.namedGroup('section')}', <String>[], language: language));
           } else {

packages/flutter/lib/src/cupertino/form_section.dart

@@ -287,7 +287,7 @@ class CupertinoFormSection extends StatelessWidget {
                 ),
                 child: Padding(
                   padding: _kDefaultHeaderMargin,
-                  child: header!,
+                  child: header,
                 ),
               ),
             ),
@@ -311,7 +311,7 @@ class CupertinoFormSection extends StatelessWidget {
                 ),
                 child: Padding(
                   padding: _kDefaultFooterMargin,
-                  child: footer!,
+                  child: footer,
                 ),
               ),
             ),

packages/flutter/lib/src/material/date_picker.dart

@@ -1652,7 +1652,7 @@ class _CalendarRangePickerDialog extends StatelessWidget {
               if (orientation == Orientation.portrait && entryModeButton != null)
                 Padding(
                   padding: const EdgeInsets.symmetric(horizontal: 8.0),
-                  child: entryModeButton!,
+                  child: entryModeButton,
                 ),
             ]),
           ),

packages/flutter/lib/src/material/dialog.dart

@@ -528,7 +528,7 @@ class AlertDialog extends StatelessWidget {
           style: contentTextStyle ?? dialogTheme.contentTextStyle ?? theme.textTheme.subtitle1!,
           child: Semantics(
             container: true,
-            child: content!,
+            child: content,
           ),
         ),
       );

packages/flutter/lib/src/material/reorderable_list.dart

@@ -557,7 +557,7 @@ class _ReorderableListViewState extends State<ReorderableListView> {
         if (widget.header != null)
           SliverPadding(
             padding: headerPadding,
-            sliver: SliverToBoxAdapter(child: widget.header!),
+            sliver: SliverToBoxAdapter(child: widget.header),
           ),
         SliverPadding(
           padding: listPadding,

packages/flutter/test/foundation/change_notifier_test.dart

@@ -454,9 +454,9 @@ void main() {
       error = e;
     }
     expect(error, isNotNull);
-    expect(error!, isFlutterError);
+    expect(error, isFlutterError);
     expect(
-      error.toStringDeep(),
+      error!.toStringDeep(),
       equalsIgnoringHashCodes(
         'FlutterError\n'
         '   A TestNotifier was used after being disposed.\n'

packages/flutter/test/services/restoration_test.dart

@@ -257,7 +257,7 @@ void main() {
         rootBucket2 = bucket;
       });
       expect(rootBucket2, isNotNull);
-      expect(rootBucket2!, isNot(same(rootBucket)));
+      expect(rootBucket2, isNot(same(rootBucket)));
       expect(manager.isReplacing, isTrue);
       expect(rootBucket2!.isReplacing, isTrue);
       await tester.idle();

packages/flutter/test/widgets/editable_text_test.dart

@@ -4861,7 +4861,7 @@ void main() {
       );
 
       expect(
-        selection!,
+        selection,
         equals(
           const TextSelection(
             baseOffset: 0,
@@ -4884,7 +4884,7 @@ void main() {
       );
 
       expect(
-        selection!,
+        selection,
         equals(
           const TextSelection(
             baseOffset: 0,
@@ -4912,7 +4912,7 @@ void main() {
       );
 
       expect(
-        selection!,
+        selection,
         equals(
           const TextSelection(
             baseOffset: 0,
@@ -4938,7 +4938,7 @@ void main() {
         platform: platform,
       );
       expect(
-        selection!,
+        selection,
         equals(
           const TextSelection(
             baseOffset: 0,
@@ -4959,7 +4959,7 @@ void main() {
         platform: platform,
       );
       expect(
-        selection!,
+        selection,
         equals(
           const TextSelection(
             baseOffset: 0,
@@ -7715,7 +7715,7 @@ class NoImplicitScrollPhysics extends AlwaysScrollableScrollPhysics {
 
   @override
   NoImplicitScrollPhysics applyTo(ScrollPhysics? ancestor) {
-    return NoImplicitScrollPhysics(parent: buildParent(ancestor)!);
+    return NoImplicitScrollPhysics(parent: buildParent(ancestor));
   }
 }
 

packages/flutter/test/widgets/focus_scope_test.dart

@@ -263,7 +263,7 @@ void main() {
       );
 
       // Add the child focus scope to the focus tree.
-      final FocusAttachment childAttachment = childFocusScope.attach(key.currentContext!);
+      final FocusAttachment childAttachment = childFocusScope.attach(key.currentContext);
       parentFocusScope.setFirstFocus(childFocusScope);
       await tester.pumpAndSettle();
       expect(childFocusScope.isFirstFocus, isTrue);

packages/flutter/test/widgets/scroll_aware_image_provider_test.dart

@@ -417,7 +417,7 @@ class RecordingPhysics extends ScrollPhysics {
 
   @override
   RecordingPhysics applyTo(ScrollPhysics? ancestor) {
-    return RecordingPhysics(parent: buildParent(ancestor)!);
+    return RecordingPhysics(parent: buildParent(ancestor));
   }
 
   @override
@@ -437,7 +437,7 @@ class ControllablePhysics extends ScrollPhysics {
 
   @override
   ControllablePhysics applyTo(ScrollPhysics? ancestor) {
-    return ControllablePhysics(parent: buildParent(ancestor)!);
+    return ControllablePhysics(parent: buildParent(ancestor));
   }
 
   @override

packages/flutter/test/widgets/shortcuts_test.dart

@@ -26,7 +26,7 @@ class TestDispatcher extends ActionDispatcher {
   @override
   Object? invokeAction(Action<TestIntent> action, Intent intent, [BuildContext? context]) {
     final Object? result = super.invokeAction(action, intent, context);
-    postInvoke?.call(action: action, intent: intent, context: context!, dispatcher: this);
+    postInvoke?.call(action: action, intent: intent, context: context, dispatcher: this);
     return result;
   }
 }

packages/flutter_test/lib/src/test_async_utils.dart

@@ -307,8 +307,9 @@ class TestAsyncUtils {
     do { // skip past frames that are from this class
       index += 1;
       assert(index < stack.length);
-      lineMatch = getClassPattern.matchAsPrefix(stack[index])!;
+      lineMatch = getClassPattern.matchAsPrefix(stack[index]);
       assert(lineMatch != null);
+      lineMatch = lineMatch!;
       assert(lineMatch.groupCount == 1);
     } while (lineMatch.group(1) == _className);
     // try to parse the stack to find the interesting frame

packages/flutter_tools/lib/src/dart/analysis.dart

@@ -137,7 +137,7 @@ class AnalysisServer {
         }
       } else if (response['error'] != null) {
         // Fields are 'code', 'message', and 'stackTrace'.
-        final Map<String, dynamic> error = castStringKeyedMap(response['error']!)!;
+        final Map<String, dynamic> error = castStringKeyedMap(response['error'])!;
         _logger.printError(
             'Error response from the server: ${error['code']} ${error['message']}');
         if (error['stackTrace'] != null) {

packages/fuchsia_remote_debug_protocol/lib/src/fuchsia_remote_connection.dart

@@ -210,7 +210,7 @@ class FuchsiaRemoteConnection {
       SshCommandRunner(
         address: address,
         interface: interface,
-        sshConfigPath: sshConfigPath!,
+        sshConfigPath: sshConfigPath,
       ),
     );
   }