Strip blockquote markers from a setext heading's continuation lines (#19878)

changelog_unreleased/markdown/19878.md

@@ -0,0 +1,20 @@
+#### Strip blockquote markers from a setext heading's continuation lines (#19878 by @Kjubikstronk)
+
+A setext heading spanning multiple lines inside a blockquote kept the `>` marker of its continuation lines as literal text.
+
+<!-- prettier-ignore -->
+```md
+<!-- Input -->
+> Multi
+> Line
+> ===
+
+<!-- Prettier stable -->
+> Multi > Line
+> ===
+
+<!-- Prettier main -->
+> Multi
+> Line
+> ===
+```

src/language-markdown/print/preprocess.js

@@ -183,8 +183,11 @@ function splitTextIntoSentences(ast) {
     // Using `node.value`, we don't need to care about markers like `\n > ` in `blockquote`s.
     let text = node.raw;
 
+    // A setext heading's text can span multiple raw source lines too, e.g.
+    // `> Title\n> continued\n> ===`.
     const paragraphIndex = parentStack.findIndex(
-      (ancestor) => ancestor?.type === "paragraph",
+      (ancestor) =>
+        ancestor?.type === "paragraph" || ancestor?.type === "heading",
     );
 
     const paragraphNode =

tests/format/markdown/heading/setext/__snapshots__/format.test.js.snap

@@ -1,5 +1,40 @@
 // Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
+exports[`blockquote.md format 1`] = `
+====================================options=====================================
+parsers: ["markdown"]
+                                                      printWidth: 80 (default) |
+=====================================input======================================
+> Multi
+> Line
+> ===
+
+> Multi
+> Line
+> Three
+> ---
+
+> > Multi
+> > Line
+> > ===
+
+=====================================output=====================================
+> Multi
+> Line
+> ===
+
+> Multi
+> Line
+> Three
+> ---
+
+> > Multi
+> > Line
+> > ===
+
+================================================================================
+`;
+
 exports[`child.md format 1`] = `
 ====================================options=====================================
 parsers: ["markdown"]

tests/format/markdown/heading/setext/blockquote.md

@@ -0,0 +1,12 @@
+> Multi
+> Line
+> ===
+
+> Multi
+> Line
+> Three
+> ---
+
+> > Multi
+> > Line
+> > ===