[Repo Assist] fix: Markdown.ToMd multi-paragraph blockquote round-trip

RELEASE_NOTES.md

@@ -17,6 +17,7 @@
 * Fix `Markdown.ToMd` serialising `HorizontalRule` as 23 hyphens regardless of the character used in the source. It now emits exactly three characters matching the parsed character (`---`, `***`, or `___`), giving faithful round-trips.
 * Remove stray `printfn` debug output emitted to stdout when `Markdown.ToMd` encountered an unrecognised paragraph type.
 * Fix `Markdown.ToLatex` producing invalid LaTeX output for level-6 (and deeper) headings. Previously the LaTeX command was an empty string, resulting in bare `{content}` without a command prefix. Headings at level 6+ are now serialised as `\subparagraph{...}`, which is the deepest sectioning command available in LaTeX.
+* Fix `Markdown.ToMd` multi-paragraph blockquote round-trip. The old code emitted a bare blank line between inner paragraphs, which CommonMark parses as closing the blockquote, resulting in multiple separate blockquotes on re-parse. Paragraph separators inside a blockquote are now emitted as `>` (an empty blockquote continuation line) so the round-trip preserves a single `QuotedBlock`.
 
 ### Added
 * Add tests for `Markdown.ToFsx` (direct serialisation to F# script format), which previously had no unit test coverage.

src/FSharp.Formatting.Markdown/MarkdownUtils.fs

@@ -307,13 +307,18 @@ module internal MarkdownUtils =
               yield ""
           | Span(body = body) -> yield formatSpans ctx body
           | QuotedBlock(paragraphs = paragraphs) ->
-              for paragraph in paragraphs do
-                  let lines = formatParagraph ctx paragraph
+              let paragraphLines =
+                  paragraphs
+                  |> List.map (fun paragraph -> formatParagraph ctx paragraph |> List.filter (fun line -> line <> ""))
 
+              for i, lines in List.indexed paragraphLines do
                   for line in lines do
                       yield "> " + line
 
-                  yield ""
+                  if i < paragraphLines.Length - 1 then
+                      yield ">"
+
+              yield ""
           | EmbedParagraphs(cmd, _) -> yield! cmd.Render() |> Seq.collect (formatParagraph ctx) ]
 
     /// Strips <c>#if SYMBOL</c> / <c>#endif // SYMBOL</c> conditional compilation lines from an .fsx code block

tests/FSharp.Markdown.Tests/Markdown.fs

@@ -1894,3 +1894,46 @@ let ``ToLatex EmbedParagraphs delegates to Render()`` () =
     let doc = MarkdownDocument([ EmbedParagraphs(inner, MarkdownRange.zero) ], dict [])
     let result = Markdown.ToLatex(doc)
     result |> should contain "latex text"
+
+// --------------------------------------------------------------------------------------
+// Markdown.ToMd: blockquote round-trip tests
+// --------------------------------------------------------------------------------------
+
+[<Test>]
+let ``ToMd preserves multi-paragraph blockquote as a single blockquote`` () =
+    // A blockquote with two paragraphs should round-trip as a *single* QuotedBlock.
+    // The old code emitted a bare blank line between paragraphs, which CommonMark
+    // interprets as closing the blockquote — resulting in two separate QuotedBlocks.
+    let md = "> First paragraph.\n>\n> Second paragraph.\n"
+    let doc = Markdown.Parse(md, newline = "\n")
+    let serialised = Markdown.ToMd(doc, newline = "\n")
+    let reparsed = Markdown.Parse(serialised, newline = "\n")
+
+    let quotedBlocks =
+        reparsed.Paragraphs
+        |> List.choose (function
+            | QuotedBlock _ as q -> Some q
+            | _ -> None)
+
+    quotedBlocks.Length |> shouldEqual 1
+
+[<Test>]
+let ``ToMd blockquote does not produce bare blank lines inside blockquote`` () =
+    // Bare blank lines (non-'>' prefixed) between inner paragraphs cause the
+    // CommonMark parser to close the blockquote early.
+    let md = "> First paragraph.\n>\n> Second paragraph.\n"
+    let doc = Markdown.Parse(md, newline = "\n")
+    let serialised = Markdown.ToMd(doc, newline = "\n")
+
+    // The separator between blockquote inner paragraphs must itself start with '>';
+    // a bare blank line ("") would close the blockquote and introduce a bug.
+    // We only look at lines that are strictly inside the blockquote section (starts with '>').
+    let lines = serialised.Split('\n')
+
+    let inBlockquote =
+        lines
+        |> Array.skipWhile (fun l -> not (l.StartsWith(">")))
+        |> Array.takeWhile (fun l -> l.StartsWith(">"))
+
+    // There should be at least two content lines (one per paragraph)
+    inBlockquote.Length |> should be (greaterThan 1)