[Flutter] TextSelectionLayout (see https://stackoverflow.com/a/46244263/1306903)

demo.dart

// animated GIF: https://i.stack.imgur.com/mHOIc.gif
// see https://stackoverflow.com/a/46244263/1306903

import 'package:flutter/material.dart';

import 'ink_text_selection_layout.dart';

class Demo extends StatelessWidget {
  @override
  Widget build(context) => inkTextSelectionLayout(
        richTextBuilder: (context) => new RichText(
              key: key,
              text: new TextSpan(
                text: 'HELLO THIS IS MY ',
                style: DefaultTextStyle.of(context).style,
                children: <TextSpan>[
                  new TextSpan(
                      text: 'LONG',
                      style: new TextStyle(fontWeight: FontWeight.bold)),
                  new TextSpan(text: ' SENTENCE'),
                ],
              ),
            ),
        selections: <TextSelection>[
          const TextSelection(
            baseOffset: 17,
            extentOffset: 21,
          ),
        ],
      );
}

ink_text_selection_layout.dart

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';

import 'text_selection_layout.dart';
export 'text_selection_layout.dart';

TextSelectionLayout inkTextSelectionLayout({
  Key key,
  TextBuilder textBuilder,
  RichTextBuilder richTextBuilder,
  @required List<TextSelection> selections,
  Rect rippleRectPadding,
  BorderRadius rippleBorderRadius,
}) {
  final padding = rippleRectPadding ?? new Rect.fromLTRB(8.0, 8.0, 8.0, 8.0);
  final radius = rippleBorderRadius ?? kMaterialEdges[MaterialType.button];

  final WidgetBuilder inkBuilder = (_) => new InkWell(
        borderRadius: radius,
        onTap: () => {},
      );

  final MergeTextBoxes mergeTextBoxes = padding == Rect.zero
      ? null
      : (textBoxes) {
          Rect rect = TextSelectionLayout.defaultMergeTextBoxes(textBoxes);
          if (rect != Rect.zero) {
            rect = new Rect.fromLTRB(
              rect.left - padding.left,
              rect.top - padding.top,
              rect.right + padding.right,
              rect.bottom + padding.bottom,
            );
          }
          return rect;
        };

  final data = selections
      .map((selection) => new TextSelectionLayoutData(
            selection: selection,
            builder: inkBuilder,
            mergeTextBoxes: mergeTextBoxes,
          ))
      .toList(growable: false);

  return new TextSelectionLayout(
    key: key,
    textBuilder: textBuilder,
    richTextBuilder: richTextBuilder,
    data: data,
  );
}

key_wrapper.dart

import 'package:flutter/material.dart';

class KeyWrapper extends StatelessWidget {
  const KeyWrapper({Key key, this.child}) : super(key: key);

  final Widget child;

  @override
  Widget build(BuildContext context) => child;
}

text_selection_layout.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/foundation.dart';

import 'dart:ui' show TextBox;
import 'dart:math';

import 'key_wrapper.dart';

typedef Text TextBuilder(BuildContext context);
typedef RichText RichTextBuilder(BuildContext context);

typedef Rect MergeTextBoxes(List<TextBox> textBoxes);

@immutable
class TextSelectionLayoutData {
  /// See [TextSelectionLayout.defaultMergeTextBoxes] for the default 
  /// implementation of [mergeTextBoxes] (used in case it's `null`).
  const TextSelectionLayoutData({
    @required this.selection,
    @required this.builder,
    this.mergeTextBoxes,
  });

  final TextSelection selection;
  final WidgetBuilder builder;
  final MergeTextBoxes mergeTextBoxes;
}

/// Provides a convenient way to place widgets in front of sections of text.
class TextSelectionLayout extends StatelessWidget {
  /// Must provide [data] and either [textBuilder] or [richTextBuilder].
  TextSelectionLayout({
    Key key,
    TextBuilder textBuilder,
    RichTextBuilder richTextBuilder,
    @required this.data,
  })
      : assert((textBuilder != null) != (richTextBuilder != null)),
        textBuilder = textBuilder ?? richTextBuilder,
        super(key: key);

  final WidgetBuilder textBuilder;
  final List<TextSelectionLayoutData> data;

  final GlobalKey _textKey = new GlobalKey();

  /// Returns a [Rect] that wraps all the [textBoxes].
  static Rect defaultMergeTextBoxes(List<TextBox> textBoxes) =>
      textBoxes?.fold(
        null,
        (Rect previous, TextBox textBox) => new Rect.fromLTRB(
              min(previous?.left ?? textBox.left, textBox.left),
              min(previous?.top ?? textBox.top, textBox.top),
              max(previous?.right ?? textBox.right, textBox.right),
              max(previous?.bottom ?? textBox.bottom, textBox.bottom),
            ),
      ) ??
      Rect.zero;

  @override
  Widget build(context) => new Stack(
        children: <Widget>[
          new KeyWrapper(
            key: _textKey,
            child: textBuilder(context),
          ),
          new Positioned.fill(
            child: new LayoutBuilder(
              builder: (context, _) => new Stack(
                    children: _getChildren(context),
                  ),
            ),
          ),
        ],
      );

  List<Positioned> _getChildren(BuildContext context) {
    if (data == null) return null;

    final RenderParagraph renderParagraph =
        _textKey.currentContext.findRenderObject() as RenderParagraph;

    return data.map((datum) {
      final List<TextBox> textBoxes =
          renderParagraph.getBoxesForSelection(datum.selection);

      final textBoxesToRect = datum.mergeTextBoxes ?? defaultMergeTextBoxes;

      final rect = textBoxesToRect(textBoxes) ?? Rect.zero;

      return new Positioned.fromRect(
        rect: rect,
        child: datum.builder(context),
      );
    }).toList(growable: false);
  }
}

@Takhion What license is this under? Thxs

@Takhion did your code work for this issue also [https://github.com/flutter/flutter/issues/26581]