Handle unsupported attributes in Markdown conversion + horizontal lines

packages/fleather/lib/src/widgets/theme.dart

@@ -29,16 +29,18 @@
   }
 
   /// The data from the closest [FleatherTheme] instance that encloses the given
-  /// context.
+  /// [context].
   ///
   /// Returns `null` if there is no [FleatherTheme] in the given build context
   /// and [nullOk] is set to `true`. If [nullOk] is set to `false` (default)
   /// then this method asserts.
   static FleatherThemeData? of(BuildContext context, {bool nullOk = false}) {
     final widget = context.dependOnInheritedWidgetOfExactType<FleatherTheme>();
     if (widget == null && nullOk) return null;
-    assert(widget != null,
-        '$FleatherTheme.of() called with a context that does not contain a FleatherTheme.');
+    assert(
+      widget != null,
+      '${FleatherTheme.of} called with a context that does not contain a $FleatherTheme.',
+    );
     return widget!.data;
   }
 }

packages/parchment/lib/src/codecs/markdown.dart

@@ -1,23 +1,25 @@
 import 'dart:convert';
 
-import 'package:parchment_delta/parchment_delta.dart';
-
-import '../document.dart';
-import '../document/attributes.dart';
-import '../document/block.dart';
-import '../document/leaf.dart';
-import '../document/line.dart';
+import 'package:parchment/parchment.dart';
 
 class ParchmentMarkdownCodec extends Codec<ParchmentDocument, String> {
-  const ParchmentMarkdownCodec();
+  const ParchmentMarkdownCodec({this.strictEncoding = true});
+
+  /// Whether to strictly stick to the Markdown syntax during the encoding.
+  ///
+  /// If this option is enabled, during the encoding, if attributes that are
+  /// not natively supported by the Markdown syntax exist, an exception will be
+  /// thrown. Otherwise, they will be converted in the best way possible
+  /// (for example with HTML tags, plain text or placeholders).
+  final bool strictEncoding;
 
   @override
   Converter<String, ParchmentDocument> get decoder =>
       _ParchmentMarkdownDecoder();
 
   @override
   Converter<ParchmentDocument, String> get encoder =>
-      _ParchmentMarkdownEncoder();
+      _ParchmentMarkdownEncoder(strict: strictEncoding);
 }
 
 class _ParchmentMarkdownDecoder extends Converter<String, ParchmentDocument> {
@@ -354,6 +356,10 @@
 }
 
 class _ParchmentMarkdownEncoder extends Converter<ParchmentDocument, String> {
+  const _ParchmentMarkdownEncoder({required this.strict});
+
+  final bool strict;
+
   static final simpleBlocks = <ParchmentAttribute, String>{
     ParchmentAttribute.bq: '> ',
     ParchmentAttribute.ul: '* ',
@@ -403,7 +409,13 @@
     ParchmentAttribute? currentBlockAttribute;
 
     void handleLine(LineNode node) {
-      if (node.hasBlockEmbed) return;
+      if (node.hasBlockEmbed) {
+        if (node.embedNode.value == BlockEmbed.horizontalRule) {
+          _writeHorizontalLineTag(buffer);
+        }
+
+        return;
+      }
 
       for (final attr in node.style.lineAttributes) {
         if (attr.key == ParchmentAttribute.block.key) {
@@ -486,8 +498,11 @@
     return buffer.toString();
   }
 
-  void _writeAttribute(StringBuffer buffer, ParchmentAttribute? attribute,
-      {bool close = false}) {
+  void _writeAttribute(
+    StringBuffer buffer,
+    ParchmentAttribute? attribute, {
+    bool close = false,
+  }) {
     if (attribute == ParchmentAttribute.bold) {
       _writeBoldTag(buffer);
     } else if (attribute == ParchmentAttribute.italic) {
@@ -497,18 +512,26 @@
     } else if (attribute == ParchmentAttribute.strikethrough) {
       _writeStrikeThoughTag(buffer);
     } else if (attribute?.key == ParchmentAttribute.link.key) {
-      _writeLinkTag(buffer, attribute as ParchmentAttribute<String>,
-          close: close);
+      _writeLinkTag(
+        buffer,
+        attribute as ParchmentAttribute<String>,
+        close: close,
+      );
     } else if (attribute?.key == ParchmentAttribute.heading.key) {
       _writeHeadingTag(buffer, attribute as ParchmentAttribute<int>);
     } else if (attribute?.key == ParchmentAttribute.block.key) {
-      _writeBlockTag(buffer, attribute as ParchmentAttribute<String>,
-          close: close);
+      _writeBlockTag(
+        buffer,
+        attribute as ParchmentAttribute<String>,
+        close: close,
+      );
     } else if (attribute?.key == ParchmentAttribute.checked.key) {
       // no-op already handled in handleBlock
     } else if (attribute?.key == ParchmentAttribute.indent.key) {
       // no-op already handled in handleBlock
-    } else {
+    } else if (!strict && attribute?.key == ParchmentAttribute.underline.key) {
+      _writeUnderlineTag(buffer, close: close);
+    } else if (strict) {
       throw ArgumentError('Cannot handle $attribute');
     }
   }
@@ -521,6 +544,14 @@
     buffer.write('_');
   }
 
+  void _writeUnderlineTag(StringBuffer buffer, {bool close = false}) {
+    if (close) {
+      buffer.write('</u>');
+    } else {
+      buffer.write('<u>');
+    }
+  }
+
   void _writeInlineCodeTag(StringBuffer buffer) {
     buffer.write('`');
   }
@@ -529,8 +560,11 @@
     buffer.write('~~');
   }
 
-  void _writeLinkTag(StringBuffer buffer, ParchmentAttribute<String> link,
-      {bool close = false}) {
+  void _writeLinkTag(
+    StringBuffer buffer,
+    ParchmentAttribute<String> link, {
+    bool close = false,
+  }) {
     if (close) {
       buffer.write('](${link.value})');
     } else {
@@ -560,4 +594,8 @@
       }
     }
   }
+
+  void _writeHorizontalLineTag(StringBuffer buffer) {
+    buffer.write('---');
+  }
 }

packages/parchment/lib/src/document/line.dart

@@ -26,6 +26,12 @@
     return false;
   }
 
+  EmbedNode get embedNode {
+    assert(hasBlockEmbed);
+
+    return children.single as EmbedNode;
+  }
+
   /// Returns next [LineNode] or `null` if this is the last line in the document.
   LineNode? get nextLine {
     if (isLast) {