iOS Text Editing Infinite Loop

shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.mm

@@ -420,6 +420,7 @@ @implementation FlutterTextInputView {
   int _textInputClient;
   const char* _selectionAffinity;
   FlutterTextRange* _selectedTextRange;
+  NSDictionary* _latestState;
 }
 
 @synthesize tokenizer = _tokenizer;
@@ -995,10 +996,36 @@ - (void)updateEditingState {
     @"text" : [NSString stringWithString:self.text],
   };
 
+  // Debounce calls to updateEditingClient on the leading edge. This makes iOS
+  // text editing behave more similarly to Android's, which has built-in event
+  // batching, and avoids race conditions. The delay value was chosen to be
+  // imperceptible by the user but still long enough to allow the framework to
+  // respond with formatting updates, thereby avoiding common race conditions.
+  if (_latestState == nil) {
+    _latestState = state;
+    [self updateEditingClient];
+    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10000000), dispatch_get_main_queue(), ^(void){
+      if (_latestState == state) {
+        _latestState = nil;
+      }
+    });
+    return;
+  }
+  _latestState = state;
+  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10000000), dispatch_get_main_queue(), ^(void){
+    if (state != _latestState) {
+      return;
+    }
+    [self updateEditingClient];
+    _latestState = nil;
+  });
+}
+
+- (void)updateEditingClient {
   if (_textInputClient == 0 && _autofillId != nil) {
-    [_textInputDelegate updateEditingClient:_textInputClient withState:state withTag:_autofillId];
+    [_textInputDelegate updateEditingClient:_textInputClient withState:_latestState withTag:_autofillId];
   } else {
-    [_textInputDelegate updateEditingClient:_textInputClient withState:state];
+    [_textInputDelegate updateEditingClient:_textInputClient withState:_latestState];
   }
 }
 

shell/platform/darwin/ios/framework/Source/FlutterTextInputPluginTest.m

@@ -174,33 +174,85 @@ - (void)testUITextInputCallsUpdateEditingStateOnce {
   FlutterTextInputView* inputView = [[FlutterTextInputView alloc] init];
   inputView.textInputDelegate = engine;
 
+  __block XCTestExpectation* expectation;
   __block int updateCount = 0;
   OCMStub([engine updateEditingClient:0 withState:[OCMArg isNotNil]])
       .andDo(^(NSInvocation* invocation) {
         updateCount++;
+        if (expectation != nil) {
+          [expectation fulfill];
+        }
       });
 
   [inputView insertText:@"text to insert"];
-  // Update the framework exactly once.
+  // The framework has been updated exactly once. It happened immediately,
+  // because calls to updateEditingState are debounced on the leading edge.
   XCTAssertEqual(updateCount, 1);
 
+  expectation = [self expectationWithDescription:@"called updateEditingClient"];
   [inputView deleteBackward];
+  // Due to the debouncing, this call will happen after a short delay.
+  XCTAssertEqual(updateCount, 1);
+  [self waitForExpectations:@[expectation] timeout:1];
+  expectation = nil;
   XCTAssertEqual(updateCount, 2);
 
+  // Subsequent calls follow this pattern of leading edge debouncing. Now that
+  // enough time has passed to allow the debouncing to call through, the
+  // debouncing is reset. The next call will happen immediately on the leading
+  // edge, and subsequent calls are debounced.
   inputView.selectedTextRange = [FlutterTextRange rangeWithNSRange:NSMakeRange(0, 1)];
   XCTAssertEqual(updateCount, 3);
 
+  expectation = [self expectationWithDescription:@"called updateEditingClient"];
   [inputView replaceRange:[FlutterTextRange rangeWithNSRange:NSMakeRange(0, 1)]
                  withText:@"replace text"];
+  XCTAssertEqual(updateCount, 3);
+  [self waitForExpectations:@[expectation] timeout:1];
+  expectation = nil;
   XCTAssertEqual(updateCount, 4);
 
   [inputView setMarkedText:@"marked text" selectedRange:NSMakeRange(0, 1)];
   XCTAssertEqual(updateCount, 5);
 
+  expectation = [self expectationWithDescription:@"called updateEditingClient"];
   [inputView unmarkText];
+  XCTAssertEqual(updateCount, 5);
+  [self waitForExpectations:@[expectation] timeout:1];
+  expectation = nil;
   XCTAssertEqual(updateCount, 6);
 }
 
+- (void)testUITextInputCallsToUpdateEditingStateAreDebounced {
+  FlutterTextInputView* inputView = [[FlutterTextInputView alloc] init];
+  inputView.textInputDelegate = engine;
+
+  __block XCTestExpectation* expectation;
+  __block int updateCount = 0;
+  OCMStub([engine updateEditingClient:0 withState:[OCMArg isNotNil]])
+      .andDo(^(NSInvocation* invocation) {
+        updateCount++;
+        if (expectation != nil) {
+          [expectation fulfill];
+        }
+      });
+
+  [inputView insertText:@"text to insert"];
+  // The framework has been updated exactly once. It happened immediately,
+  // because calls to updateEditingState are debounced on the leading edge.
+  XCTAssertEqual(updateCount, 1);
+
+  // These calls will be batched and come through after a short delay.
+  expectation = [self expectationWithDescription:@"called updateEditingClient twice"];
+  [inputView deleteBackward];
+  [inputView deleteBackward];
+  [inputView deleteBackward];
+  XCTAssertEqual(updateCount, 1);
+  [self waitForExpectations:@[expectation] timeout:1];
+  XCTAssertEqual(updateCount, 2);
+  XCTAssertTrue([inputView.text isEqualToString:@"text to ins"]);
+}
+
 - (void)testTextChangesTriggerUpdateEditingClient {
   FlutterTextInputView* inputView = [[FlutterTextInputView alloc] init];
   inputView.textInputDelegate = engine;
@@ -314,6 +366,17 @@ - (void)testUpdateEditingClientSelectionClamping {
   FlutterTextInputView* inputView = [[FlutterTextInputView alloc] init];
   inputView.textInputDelegate = engine;
 
+  // Debounced calls need to be waited for using this expectation.
+  __block XCTestExpectation* expectation;
+  __block int updateCount = 0;
+  OCMStub([engine updateEditingClient:0 withState:[OCMArg isNotNil]])
+      .andDo(^(NSInvocation* invocation) {
+        updateCount++;
+        if (expectation != nil) {
+          [expectation fulfill];
+        }
+      });
+
   [inputView.text setString:@"SELECTION"];
   inputView.markedTextRange = nil;
   inputView.selectedTextRange = nil;
@@ -328,13 +391,16 @@ - (void)testUpdateEditingClientSelectionClamping {
                               }]]);
 
   // Needs clamping.
+  expectation = [self expectationWithDescription:@"called updateEditingClient"];
   [inputView setTextInputState:@{
     @"text" : @"SELECTION",
     @"selectionBase" : @0,
     @"selectionExtent" : @9999
   }];
   [inputView updateEditingState];
 
+  [self waitForExpectations:@[expectation] timeout:1];
+  expectation = nil;
   OCMVerify([engine updateEditingClient:0
                               withState:[OCMArg checkWithBlock:^BOOL(NSDictionary* state) {
                                 return ([state[@"selectionBase"] intValue]) == 0 &&
@@ -352,12 +418,15 @@ - (void)testUpdateEditingClientSelectionClamping {
                               }]]);
 
   // Both ends need clamping.
+  expectation = [self expectationWithDescription:@"called updateEditingClient"];
   [inputView setTextInputState:@{
     @"text" : @"SELECTION",
     @"selectionBase" : @9999,
     @"selectionExtent" : @9999
   }];
   [inputView updateEditingState];
+  [self waitForExpectations:@[expectation] timeout:1];
+  expectation = nil;
   OCMVerify([engine updateEditingClient:0
                               withState:[OCMArg checkWithBlock:^BOOL(NSDictionary* state) {
                                 return ([state[@"selectionBase"] intValue]) == 9 &&