fix(formatter_markdown): keep blank line between HTML and nested list (#27112)

Otherwise, output is not idempotent.

crates/oxc_formatter_markdown/DIVERGENCES.md

@@ -211,6 +211,37 @@ though no type 7 block can interrupt a paragraph on a regular line.
 Printed with the container's prefix the line is no longer lazy, so a blank line keeps the block apart;
 Prettier prints it adjacent, and the next parse reads it as part of the paragraph.
 
+## list-after-html-block
+
+- Why: semantics (prettier/prettier#17690)
+- Pin: `tests/fixtures/markdown/list-after-html-block.md`
+
+```markdown
+<!-- input -->
+- a
+
+  <div>
+
+  - b
+
+<!-- ours -->
+- a
+
+  <div>
+
+  - b
+
+<!-- prettier (the list item becomes html, one per pass) -->
+- a
+
+  <div>
+  - b
+```
+
+A nested list after a type 6 / 7 HTML block keeps its blank line: only a blank line ends such a block.
+Prettier joins any list in a list item to the previous block, and the next parse reads the first list line as part of the html.
+Types 1 to 5 end at their end marker, so a list after them is printed adjacent as Prettier does.
+
 ## list-marker-after-ignored-list
 
 - Why: semantics

crates/oxc_formatter_markdown/src/print/block.rs

@@ -113,10 +113,12 @@ fn double_gap(
         return !after_definition && !multi_line;
     }
 
-    // A nested list after a paragraph / code keeps its blank line (prettier#17746)
+    // A nested list after a paragraph / code keeps its blank line, and after a type 6 / 7 HTML block,
+    // which only a blank line ends (DIVERGENCES.md#list-after-html-block)
     if matches!(node, Block::List(_))
         && matches!(parent, Parent::ListItem { .. })
-        && matches!(previous, Block::CodeBlock(_) | Block::Paragraph(_))
+        && (matches!(previous, Block::CodeBlock(_) | Block::Paragraph(_))
+            || matches!(previous, Block::HtmlBlock(h) if h.kind >= 6))
         && !adjacent
     {
         return true;

crates/oxc_formatter_markdown/tests/fixtures/markdown/list-after-html-block.md

@@ -0,0 +1,30 @@
+- list
+
+  <details><summary></summary>
+
+  1. item
+
+  2. item
+
+  </details>
+
+- list
+
+  <div>
+
+  - item
+  - item
+
+  </div>
+
+- list
+
+  <custom-tag>
+
+  - item
+
+- list
+
+  <!-- closed by its end marker -->
+
+  - item

crates/oxc_formatter_markdown/tests/fixtures/markdown/list-after-html-block.md.snap

@@ -0,0 +1,104 @@
+---
+source: crates/oxc_formatter_markdown/tests/fixtures/mod.rs
+assertion_line: 50
+---
+==================== Input ====================
+- list
+
+  <details><summary></summary>
+
+  1. item
+
+  2. item
+
+  </details>
+
+- list
+
+  <div>
+
+  - item
+  - item
+
+  </div>
+
+- list
+
+  <custom-tag>
+
+  - item
+
+- list
+
+  <!-- closed by its end marker -->
+
+  - item
+
+==================== Output ====================
+------------------
+{ printWidth: 80 }
+------------------
+- list
+
+  <details><summary></summary>
+
+  1. item
+
+  2. item
+
+  </details>
+
+- list
+
+  <div>
+
+  - item
+  - item
+
+  </div>
+
+- list
+
+  <custom-tag>
+
+  - item
+
+- list
+
+  <!-- closed by its end marker -->
+  - item
+
+-------------------
+{ printWidth: 100 }
+-------------------
+- list
+
+  <details><summary></summary>
+
+  1. item
+
+  2. item
+
+  </details>
+
+- list
+
+  <div>
+
+  - item
+  - item
+
+  </div>
+
+- list
+
+  <custom-tag>
+
+  - item
+
+- list
+
+  <!-- closed by its end marker -->
+  - item
+
+===================== End =====================