[flutter_markdown] Strip leading whitespace from list items (flutter#5294)

In line with standard Markdown practice, whitespace at the beginning of list items is removed.

Fixes [Flutter issue flutter#134847
](flutter#134847)

Author: krozett

packages/flutter_markdown/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.18+2
+
+* Removes leading whitespace from list items.
+
 ## 0.6.18+1
 
 * Fixes a typo in README.

packages/flutter_markdown/lib/src/builder.dart

@@ -323,7 +323,8 @@ class MarkdownBuilder implements md.NodeVisitor {
       // Leading spaces in paragraph or list item are ignored
       // https://github.github.com/gfm/#example-192
       // https://github.github.com/gfm/#example-236
-      if (const <String>['ul', 'ol', 'p', 'br'].contains(_lastVisitedTag)) {
+      if (const <String>['ul', 'ol', 'li', 'p', 'br']
+          .contains(_lastVisitedTag)) {
         text = text.replaceAll(leadingSpacesPattern, '');
       }
 

packages/flutter_markdown/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Markdown renderer for Flutter. Create rich text output,
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.6.18+1
+version: 0.6.18+2
 
 environment:
   sdk: ">=3.0.0 <4.0.0"

packages/flutter_markdown/test/list_test.dart

@@ -72,6 +72,28 @@ void defineTests() {
         'two',
       ]);
     });
+
+    testWidgets(
+      'leading spaces are ignored (non-paragraph test case)',
+      (WidgetTester tester) async {
+        const String data = '- one\n-  two\n-   three';
+        await tester.pumpWidget(
+          boilerplate(
+            const MarkdownBody(data: data),
+          ),
+        );
+
+        final Iterable<Widget> widgets = tester.allWidgets;
+        expectTextStrings(widgets, <String>[
+          '•',
+          'one',
+          '•',
+          'two',
+          '•',
+          'three',
+        ]);
+      },
+    );
   });
 
   group('Ordered List', () {