content [nfc]: Track recognizer on inline tree, apply to text spans

At this stage the recognizer is always null and so this doesn't
do anything.  But it provides us the infrastructure with which to
start recognizing taps on links, #71.

Author: gnprice

lib/widgets/content.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:html/dom.dart' as dom;
 
@@ -302,7 +303,7 @@ Widget _buildBlockInlineContainer({
   required BlockInlineContainerNode node,
 }) {
   if (node.links == null) {
-    return InlineContent(style: style, nodes: node.nodes);
+    return InlineContent(recognizer: null, style: style, nodes: node.nodes);
   }
   return _BlockInlineContainer(
     links: node.links!, style: style, nodes: node.nodes);
@@ -323,21 +324,24 @@ class _BlockInlineContainer extends StatefulWidget {
 class _BlockInlineContainerState extends State<_BlockInlineContainer> {
   @override
   Widget build(BuildContext context) {
-    return InlineContent(style: widget.style, nodes: widget.nodes);
+    return InlineContent(recognizer: null,
+      style: widget.style, nodes: widget.nodes);
   }
 }
 
 class InlineContent extends StatelessWidget {
   InlineContent({
     super.key,
-    required this.nodes,
+    required this.recognizer,
     required this.style,
+    required this.nodes,
   }) {
     _builder = _InlineContentBuilder(this);
   }
 
-  final List<InlineContentNode> nodes;
+  final GestureRecognizer? recognizer;
   final TextStyle? style;
+  final List<InlineContentNode> nodes;
 
   late final _InlineContentBuilder _builder;
 
@@ -348,14 +352,21 @@ class InlineContent extends StatelessWidget {
 }
 
 class _InlineContentBuilder {
-  _InlineContentBuilder(this.widget);
+  _InlineContentBuilder(this.widget) : _recognizer = widget.recognizer;
 
   final InlineContent widget;
 
   InlineSpan build() {
     return _buildNodes(widget.nodes, style: widget.style);
   }
 
+  // Why do we have to track `recognizer` here, rather than apply it
+  // once at the top of the affected span?  Because the events don't bubble
+  // within a paragraph:
+  //   https://github.com/flutter/flutter/issues/10623
+  //   https://github.com/flutter/flutter/issues/10623#issuecomment-308030170
+  final GestureRecognizer? _recognizer;
+
   InlineSpan _buildNodes(List<InlineContentNode> nodes, {required TextStyle? style}) {
     return TextSpan(
       style: style,
@@ -364,7 +375,7 @@ class _InlineContentBuilder {
 
   InlineSpan _buildNode(InlineContentNode node) {
     if (node is TextNode) {
-      return TextSpan(text: node.text);
+      return TextSpan(text: node.text, recognizer: _recognizer);
     } else if (node is LineBreakInlineNode) {
       // Each `<br/>` is followed by a newline, which browsers apparently ignore
       // and our parser doesn't.  So don't do anything here.
@@ -401,7 +412,7 @@ class _InlineContentBuilder {
     style: const TextStyle(fontStyle: FontStyle.italic));
 
   InlineSpan _buildLink(LinkNode node) {
-    // TODO make link touchable
+    // TODO make link touchable by setting _recognizer
     return _buildNodes(node.nodes,
       style: TextStyle(color: const HSLColor.fromAHSL(1, 200, 1, 0.4).toColor()));
   }
@@ -497,7 +508,11 @@ class UserMention extends StatelessWidget {
     return Container(
       decoration: _kDecoration,
       padding: const EdgeInsets.symmetric(horizontal: 0.2 * kBaseFontSize),
-      child: InlineContent(nodes: node.nodes, style: null));
+      child: InlineContent(
+        // If an @-mention is inside a link, let the @-mention override it.
+        recognizer: null,  // TODO make @-mentions tappable, for info on user
+        style: null,
+        nodes: node.nodes));
   }
 
   static get _kDecoration => BoxDecoration(