feat(portable_text): expose block index to BlockContainerBuilder

packages/sanity/flutter_sanity_portable_text/README.md

@@ -512,8 +512,10 @@ class MyApp extends StatelessWidget {
 Widget columnBuilder(BuildContext context, List<PortableBlockItem> blocks) {
   return Column(
     children: blocks
-        .map(
-            (block) => PortableTextConfig.shared.buildBlock(context, block))
+        .asMap()
+        .entries
+        .map((entry) =>
+            PortableTextConfig.shared.buildBlock(context, entry.value, entry.key))
         .toList(),
   );
 }

packages/sanity/flutter_sanity_portable_text/lib/ui/portable_text_block.dart

@@ -14,7 +14,12 @@ class PortableTextBlock extends StatelessWidget {
   /// The model representing the block of Portable Text.
   final TextBlockItem model;
 
-  const PortableTextBlock({super.key, required this.model});
+  /// The position of this block within its parent list (0-based). Passed on to
+  /// the [BlockContainerBuilder] so containers can vary by position (e.g. drop
+  /// leading space on the first block). Defaults to 0 for standalone use.
+  final int index;
+
+  const PortableTextBlock({super.key, required this.model, this.index = 0});
 
   @override
   Widget build(final BuildContext context) {
@@ -36,7 +41,7 @@ class PortableTextBlock extends StatelessWidget {
     final builder = config.blockContainers[model.style] ??
         PortableTextConfig.defaultBlockContainerBuilder;
 
-    final child = builder(context, content);
+    final child = builder(context, content, index);
 
     final leftPadding =
         model.listItem == null ? 0.0 : config.listIndent * (model.level ?? 0);

packages/sanity/flutter_sanity_portable_text/lib/ui/portable_text_config.dart

@@ -9,12 +9,23 @@ typedef TextStyleBuilder = TextStyle Function(
 );
 
 /// A function that builds a widget for a Portable block container.
-typedef BlockContainerBuilder = Widget Function(BuildContext, Widget);
+///
+/// [index] is the position of the block within its parent list (0-based), which
+/// lets containers vary by position — e.g. suppressing leading space on the
+/// first block.
+typedef BlockContainerBuilder = Widget Function(
+  BuildContext context,
+  Widget child,
+  int index,
+);
 
 /// A function that builds a widget for a Portable block item.
+///
+/// [index] is the position of the block within its parent list (0-based).
 typedef BlockWidgetBuilder = Widget Function(
   BuildContext context,
   PortableBlockItem item,
+  int index,
 );
 
 /// A function that builds an InlineSpan for a single bullet mark. Using the
@@ -97,15 +108,19 @@ final class PortableTextConfig {
   /// Builds a block widget for the given Portable block item.
   /// The block widget is determined by the block type of the item. If the block type is not found in the
   /// block widgets, an error view is rendered with a message indicating the missing block type.
-  Widget buildBlock(final BuildContext context, final PortableBlockItem item) {
+  Widget buildBlock(
+    final BuildContext context,
+    final PortableBlockItem item,
+    final int index,
+  ) {
     final type = item.blockType;
 
     final builder = blocks[type];
     if (builder == null) {
       return ErrorView(message: 'Missing builder for block "$type"');
     }
 
-    return builder(context, item);
+    return builder(context, item, index);
   }
 
   /// Resets the shared instance of the [PortableTextConfig] to the default configuration.
@@ -167,7 +182,7 @@ final class PortableTextConfig {
   }
 
   static BlockContainerBuilder defaultBlockContainerBuilder =
-      (final BuildContext context, final Widget child) {
+      (final BuildContext context, final Widget child, final int index) {
     return child;
   };
 
@@ -269,7 +284,8 @@ final class PortableTextConfig {
 
   /// The default block containers used by the shared instance of [PortableTextConfig].
   static final Map<String, BlockContainerBuilder> defaultBlockContainers = {
-    'blockquote': (final BuildContext context, final Widget child) {
+    'blockquote':
+        (final BuildContext context, final Widget child, final int index) {
       final theme = Theme.of(context);
 
       return Container(
@@ -293,8 +309,9 @@ final class PortableTextConfig {
   /// The default block widgets used by the shared instance of [PortableTextConfig].
   /// The default block is a single [PortableTextBlock], named as "block".
   static final Map<String, BlockWidgetBuilder> defaultBlocks = {
-    'block': (final context, final item) => PortableTextBlock(
+    'block': (final context, final item, final index) => PortableTextBlock(
           model: item as TextBlockItem,
+          index: index,
         ),
   };
 }

packages/sanity/flutter_sanity_portable_text/lib/ui/portable_text_widget.dart

@@ -45,6 +45,6 @@ Widget defaultListBuilder(
     itemCount: blocks.length,
     padding: EdgeInsets.zero,
     itemBuilder: (final context, final index) =>
-        PortableTextConfig.shared.buildBlock(context, blocks[index]),
+        PortableTextConfig.shared.buildBlock(context, blocks[index], index),
   );
 }

packages/sanity/flutter_sanity_portable_text/test/custom_test.dart

@@ -70,7 +70,7 @@ void main() {
   testWidgets('PortableText can apply a custom block',
       (WidgetTester tester) async {
     PortableTextConfig.shared.blocks[_CustomBlockItem.schemaName] =
-        (context, item) {
+        (context, item, index) {
       return const Text('Hello, World');
     };
 
@@ -91,7 +91,7 @@ void main() {
       return const TextStyle(color: Colors.red);
     };
     PortableTextConfig.shared.blockContainers['custom-block'] =
-        (context, child) {
+        (context, child, index) {
       return Container(
         color: Colors.red,
         child: child,

packages/sanity/flutter_sanity_portable_text/test/fundamentals_test.dart

@@ -34,8 +34,10 @@ void main() {
     Widget columnBuilder(BuildContext context, List<PortableBlockItem> blocks) {
       return Column(
         children: blocks
-            .map(
-                (block) => PortableTextConfig.shared.buildBlock(context, block))
+            .asMap()
+            .entries
+            .map((entry) => PortableTextConfig.shared
+                .buildBlock(context, entry.value, entry.key))
             .toList(),
       );
     }