Optionally show the text field length but not the max (#24183)

If maxLength is set to TextField.noMaxLength then continue to show the character counter but do not display the max input length value.

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

@@ -78,7 +78,10 @@ class TextField extends StatefulWidget {
   /// number of characters allowed in the text field is not restricted. If
   /// [maxLength] is set, a character counter will be displayed below the
   /// field, showing how many characters have been entered and how many are
-  /// allowed. After [maxLength] characters have been input, additional input
+  /// allowed unless the value is set to [noMaxLength] in which case only the
+  /// current length is displayed.
+  ///
+  /// After [maxLength] characters have been input, additional input
   /// is ignored, unless [maxLengthEnforced] is set to false. The TextField
   /// enforces the length with a [LengthLimitingTextInputFormatter], which is
   /// evaluated after the supplied [inputFormatters], if any. The [maxLength]
@@ -192,6 +195,10 @@ class TextField extends StatefulWidget {
   /// {@macro flutter.widgets.editableText.maxLines}
   final int maxLines;
 
+  /// If [maxLength] is set to this value, only the "current input length"
+  /// part of the character counter is shown.
+  static const int noMaxLength = 9007199254740992; // math.pow(2, 53);
+
   /// The maximum number of characters (Unicode scalar values) to allow in the
   /// text field.
   ///
@@ -339,9 +346,16 @@ class _TextFieldState extends State<TextField> with AutomaticKeepAliveClientMixi
       return effectiveDecoration;
 
     final int currentLength = _effectiveController.value.text.runes.length;
-    final String counterText = '$currentLength/${widget.maxLength}';
+    String counterText = '$currentLength';
+    String semanticCounterText = '';
+
+    if (widget.maxLength != TextField.noMaxLength) {
+      counterText += '/${widget.maxLength}';
       final int remaining = (widget.maxLength - currentLength).clamp(0, widget.maxLength);
-    final String semanticCounterText = localizations.remainingTextFieldCharacterCount(remaining);
+      semanticCounterText = localizations.remainingTextFieldCharacterCount(remaining);
+    }
+
+    // Handle length exceeds maxLength
     if (_effectiveController.value.text.runes.length > widget.maxLength) {
       final ThemeData themeData = Theme.of(context);
       return effectiveDecoration.copyWith(

packages/flutter/test/material/text_field_test.dart

@@ -1790,8 +1790,6 @@ void main() {
   testWidgets('setting maxLength shows counter', (WidgetTester tester) async {
     await tester.pumpWidget(const MaterialApp(
       home: Material(
-        child: DefaultTextStyle(
-          style: TextStyle(fontFamily: 'Ahem', fontSize: 10.0),
         child: Center(
             child: TextField(
               maxLength: 10,
@@ -1799,7 +1797,7 @@ void main() {
           ),
         ),
       ),
-    ));
+    );
 
     expect(find.text('0/10'), findsOneWidget);
 
@@ -1809,14 +1807,34 @@ void main() {
     expect(find.text('5/10'), findsOneWidget);
   });
 
+  testWidgets(
+      'setting maxLength to TextField.noMaxLength shows only entered length',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(const MaterialApp(
+      home: Material(
+        child: Center(
+            child: TextField(
+              maxLength: TextField.noMaxLength,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(find.text('0'), findsOneWidget);
+
+    await tester.enterText(find.byType(TextField), '01234');
+    await tester.pump();
+
+    expect(find.text('5'), findsOneWidget);
+  });
+
   testWidgets('TextField identifies as text field in semantics', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);
 
     await tester.pumpWidget(
       const MaterialApp(
         home: Material(
-          child: DefaultTextStyle(
-            style: TextStyle(fontFamily: 'Ahem', fontSize: 10.0),
           child: Center(
               child: TextField(
                 maxLength: 10,
@@ -1824,7 +1842,6 @@ void main() {
             ),
           ),
         ),
-      ),
     );
 
     expect(semantics, includesNodeWith(flags: <SemanticsFlag>[SemanticsFlag.isTextField]));
@@ -3162,9 +3179,7 @@ void main() {
     await tester.pumpWidget(
       MaterialApp(
         home: Scaffold(
-          body: DefaultTextStyle(
-            style: const TextStyle(fontSize: 12.0, fontFamily: 'Ahem'),
-            child: MediaQuery(
+          body: MediaQuery(
               data: MediaQueryData.fromWindow(ui.window).copyWith(textScaleFactor: 4.0),
               child: Center(
                 child: TextField(
@@ -3175,7 +3190,6 @@ void main() {
             ),
           ),
         ),
-      ),
     );
 
     await tester.tap(find.byType(TextField));