gistfile1.txt

import 'package:flutter/material.dart';

class NoSplashFactory extends InteractiveInkFeatureFactory {
  const NoSplashFactory();

  @override
  InteractiveInkFeature create({
    @required MaterialInkController controller,
    @required RenderBox referenceBox,
    @required Offset position,
    @required Color color,
    bool containedInkWell: false,
    RectCallback rectCallback,
    BorderRadius borderRadius,
    double radius,
    VoidCallback onRemoved,
  }) {
    return new NoSplash(
      controller: controller,
      referenceBox: referenceBox,
      color: color,
      onRemoved: onRemoved,
    );
  }
}

class NoSplash extends InteractiveInkFeature {
  NoSplash({
    @required MaterialInkController controller,
    @required RenderBox referenceBox,
    Color color,
    VoidCallback onRemoved,
  }) : assert(controller != null),
       assert(referenceBox != null),
       super(controller: controller, referenceBox: referenceBox, onRemoved: onRemoved) {
    // Added per https://github.com/flutter/flutter/issues/20874
    controller.addInkFeature(this);
  }
  @override
  void paintFeature(Canvas canvas, Matrix4 transform) { }
}

class TextFieldsPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(title: const Text('TextFields')),
      body: new Container(
        padding: const EdgeInsets.all(48.0),
        alignment: Alignment.topLeft,
        child: new Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            new Theme(
              data: Theme.of(context).copyWith(
                splashFactory: const NoSplashFactory(),
              ),
              child: new TextField(),
            ),
            const SizedBox(height: 24.0),
            new TextField(),
          ],
        ),
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(title: const Text('NoSplashFactory')),
      body: new Center(
        child: new RaisedButton(
          child: const Text('Push TextFields Page'),
          onPressed: () {
            Navigator.of(context).push(
              new MaterialPageRoute(builder: (BuildContext context) => new TextFieldsPage()),
            );
          },
        ),
      ),
    );
  }
}

void main() {
  runApp(
    new MaterialApp(
      home: new HomePage(),
    ),
  );
}

With 1.5.4-hotfix.2

class NoSplashFactory extends InteractiveInkFeatureFactory {
  const NoSplashFactory();

  @override
  InteractiveInkFeature create({
    @required MaterialInkController controller,
    @required RenderBox referenceBox,
    @required Offset position,
    @required Color color,
    @required TextDirection textDirection,
    bool containedInkWell = false,
    RectCallback rectCallback,
    BorderRadius borderRadius,
    ShapeBorder customBorder,
    double radius,
    VoidCallback onRemoved,
  }) {
    return NoSplash(
      controller: controller,
      referenceBox: referenceBox,
      color: color,
      onRemoved: onRemoved,
    );
  }
}

class NoSplash extends InteractiveInkFeature {
  NoSplash({
    @required MaterialInkController controller,
    @required RenderBox referenceBox,
    Color color,
    VoidCallback onRemoved,
  })  : assert(controller != null),
        assert(referenceBox != null),
        super(controller: controller, referenceBox: referenceBox, onRemoved: onRemoved) {
    controller.addInkFeature(this);
  }
  @override
  void paintFeature(Canvas canvas, Matrix4 transform) {}
}

+1

For 2.20:

import 'package:flutter/material.dart';

class NoSplashFactory extends InteractiveInkFeatureFactory {
  const NoSplashFactory();

  @override
  InteractiveInkFeature create({
    required MaterialInkController controller,
    required RenderBox referenceBox,
    required Offset position,
    required Color color,
    required TextDirection textDirection,
    bool containedInkWell = false,
    RectCallback? rectCallback,
    BorderRadius? borderRadius,
    ShapeBorder? customBorder,
    double? radius,
    VoidCallback? onRemoved,
  }) {
    return InkSplash(
      controller: controller,
      referenceBox: referenceBox,
      position: position,
      color: color,
      containedInkWell: containedInkWell,
      rectCallback: rectCallback,
      borderRadius: borderRadius,
      customBorder: customBorder,
      radius: radius,
      onRemoved: onRemoved,
      textDirection: textDirection,
    );
  }
}

class InkSplash extends InteractiveInkFeature {
  InkSplash({
    required MaterialInkController controller,
    required RenderBox referenceBox,
    required TextDirection textDirection,
    Offset? position,
    required Color color,
    bool containedInkWell = false,
    RectCallback? rectCallback,
    BorderRadius? borderRadius,
    ShapeBorder? customBorder,
    double? radius,
    VoidCallback? onRemoved,
  }) : super(
            controller: controller,
            referenceBox: referenceBox,
            color: color,
            onRemoved: onRemoved) {
    controller.addInkFeature(this);
  }

  @override
  void paintFeature(Canvas canvas, Matrix4 transform) {}
}