Revert changes made in PR flutter#235 (flutter#264)

Author: mjordan56

packages/flutter_markdown/lib/src/widget.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
+
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -200,19 +202,20 @@ class _MarkdownWidgetState extends State<MarkdownWidget>
 
     _disposeRecognizers();
 
-    /// FIXME: Enhance it using a single RegEx
-    final List<String> lines = widget.data
-        .replaceAll(RegExp(r'[ ]{2}(\r?\n)'), '  &amp;')
-        .split(RegExp(r'\r?\n'))
-        .map((e) => e?.replaceAll(RegExp(r'  &amp;'), '  \n'))
-        .toList();
     final md.Document document = md.Document(
       extensionSet: widget.extensionSet ?? md.ExtensionSet.gitHubFlavored,
       inlineSyntaxes: (widget.extensionSet?.inlineSyntaxes ?? [])
         ..add(TaskListSyntax())
         ..map((syntax) => syntax),
       encodeHtml: false,
     );
+
+    // Parse the source Markdown data into nodes of an Abstract Syntax Tree.
+    final List<String> lines = LineSplitter().convert(widget.data);
+    final List<md.Node> astNodes = document.parseLines(lines);
+
+    // Configure a Markdown widget builder to traverse the AST nodes and
+    // create a widget tree based on the elements.
     final MarkdownBuilder builder = MarkdownBuilder(
       delegate: this,
       selectable: widget.selectable,
@@ -223,7 +226,8 @@ class _MarkdownWidgetState extends State<MarkdownWidget>
       builders: widget.builders,
       fitContent: widget.fitContent,
     );
-    _children = builder.build(document.parseLines(lines));
+
+    _children = builder.build(astNodes);
   }
 
   void _disposeRecognizers() {

packages/flutter_markdown/test/flutter_markdown_test.dart

@@ -70,34 +70,54 @@ void main() {
     _expectTextStrings(widgets, <String>['strikethrough']);
   });
 
-  testWidgets('Single line break', (WidgetTester tester) async {
-    await tester
-        .pumpWidget(_boilerplate(const MarkdownBody(data: 'line 1  \nline 2')));
+  group('Line Breaks', () {
+    testWidgets(
+      // Example 654 from the GitHub Flavored Markdown specification.
+      'Two spaces at end of line inside a block element',
+      (WidgetTester tester) async {
+        await tester.pumpWidget(
+            _boilerplate(const MarkdownBody(data: 'line 1  \nline 2')));
+
+        final Iterable<Widget> widgets = tester.allWidgets;
+        _expectWidgetTypes(widgets,
+            <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
+        _expectTextStrings(widgets, <String>['line 1\nline 2']);
+      },
+    );
 
-    final Iterable<Widget> widgets = tester.allWidgets;
-    _expectWidgetTypes(
-        widgets, <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
-    _expectTextStrings(widgets, <String>['line 1\nline 2']);
-  });
+    testWidgets(
+      // Example 655 from the GitHub Flavored Markdown specification.
+      'Backslash at end of line inside a block element',
+      (WidgetTester tester) async {
+        await tester.pumpWidget(
+            _boilerplate(const MarkdownBody(data: 'line 1\\\nline 2')));
+
+        final Iterable<Widget> widgets = tester.allWidgets;
+        _expectWidgetTypes(widgets,
+            <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
+        _expectTextStrings(widgets, <String>['line 1\nline 2']);
+      },
+    );
 
-  testWidgets('Multiple line breaks', (WidgetTester tester) async {
-    await tester.pumpWidget(
-        _boilerplate(const MarkdownBody(data: 'line 1  \n  \nline 2')));
+    testWidgets('Non-applicable line break', (WidgetTester tester) async {
+      final body = MarkdownBody(data: 'line 1.\nline 2.');
+      await tester.pumpWidget(_boilerplate(body));
 
-    final Iterable<Widget> widgets = tester.allWidgets;
-    _expectWidgetTypes(
-        widgets, <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
-    _expectTextStrings(widgets, <String>['line 1\n\nline 2']);
-  });
+      final Iterable<Widget> widgets = tester.allWidgets;
+      _expectWidgetTypes(widgets,
+          <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
+      _expectTextStrings(widgets, <String>['line 1. line 2.']);
+    });
 
-  testWidgets('Non-applicable line break', (WidgetTester tester) async {
-    final body = MarkdownBody(data: 'line 1.\nline 2.');
-    await tester.pumpWidget(_boilerplate(body));
+    testWidgets('Non-applicable line break', (WidgetTester tester) async {
+      final body = MarkdownBody(data: 'line 1.\nline 2.');
+      await tester.pumpWidget(_boilerplate(body));
 
-    final Iterable<Widget> widgets = tester.allWidgets;
-    _expectWidgetTypes(
-        widgets, <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
-    _expectTextStrings(widgets, <String>['line 1. line 2.']);
+      final Iterable<Widget> widgets = tester.allWidgets;
+      _expectWidgetTypes(widgets,
+          <Type>[Directionality, MarkdownBody, Column, Wrap, RichText]);
+      _expectTextStrings(widgets, <String>['line 1. line 2.']);
+    });
   });
 
   testWidgets('Empty string', (WidgetTester tester) async {