fix: leave Quarto's book title-block code block alone

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
 - fix: The HTML dependency folder now uses the extension version, so browsers load the new files after an upgrade. (#88)
+- fix: Leave alone the code block that Quarto adds for a chapter's front matter in a book rendered to one file, so no empty `quarto-title-block` window shows at the start of the chapter. (#89)
 
 ## 1.8.2 (2026-11-05)
 

_extensions/code-window/code-window.lua

@@ -113,6 +113,14 @@ local function is_unnamed_cell_output(block)
   return cell_output.is_marked(block) and str.is_empty(block.attributes['filename'])
 end
 
+--- Check whether a block holds a chapter's front matter, which Quarto writes
+--- in a book rendered to one file and later replaces with the title block.
+--- @param block pandoc.CodeBlock Code block element
+--- @return boolean
+local function is_quarto_block(block)
+  return block.classes:includes('quarto-title-block')
+end
+
 -- ============================================================================
 -- BLOCK-LEVEL STYLE OVERRIDE
 -- ============================================================================
@@ -970,6 +978,10 @@ end
 --- that rather than skipping validation for the same kind of block, so the
 --- same document reports the same finding in both formats.
 function CodeBlock(block)
+  if is_quarto_block(block) then
+    return nil
+  end
+
   -- The Typst path reads the marker in the Pandoc filter, which runs first, so
   -- this pass is where it is removed for every format.
   local is_plain_output = is_unnamed_cell_output(block)
@@ -1056,6 +1068,10 @@ end
 --- @return boolean consumed_next Whether the next block was consumed
 --- @return integer|nil annotation_block_id Block ID if annotations were found (for parent propagation)
 local function process_typst_block(block, next_block)
+  if is_quarto_block(block) then
+    return { block }, false, nil
+  end
+
   -- Check this block's own attributes against the CodeBlock group of the
   -- schema before anything below reads or rewrites them, in either branch.
   local resolved, auto_label = resolve_and_take(block)
@@ -1383,4 +1399,5 @@ return {
   CodeBlock = CodeBlock,
   CONFIG = function() return CONFIG end,
   draws_chrome = draws_chrome,
+  is_quarto_block = is_quarto_block,
 }

_extensions/code-window/main.lua

@@ -87,7 +87,7 @@ end
 --- @param block pandoc.CodeBlock
 --- @return pandoc.CodeBlock|nil Relabelled block, or nil when the pass is skipped
 local function normalise_language(block)
-  if not code_window.draws_chrome() then
+  if not code_window.draws_chrome() or code_window.is_quarto_block(block) then
     return nil
   end
   if not code_window.CONFIG().auto_filename then

tests/fixtures/book/_quarto.yml

@@ -0,0 +1,16 @@
+project:
+  type: book
+
+book:
+  title: "Book title block"
+  author: "Code Window"
+  chapters:
+    - index.qmd
+    - chapter.qmd
+
+filters:
+  - code-window
+
+format:
+  typst:
+    keep-typ: true

tests/fixtures/book/chapter.qmd

@@ -0,0 +1,9 @@
+---
+title: "Chapter with front matter"
+---
+
+Quarto puts this front matter into a code block of its own, which code-window must leave alone.
+
+```r
+x <- 1
+```

tests/fixtures/book/index.qmd

@@ -0,0 +1,3 @@
+# Preface {.unnumbered}
+
+A chapter with no front matter of its own.

tests/run.sh

@@ -38,10 +38,15 @@ report() {
 	fi
 }
 
-# Render a fixture, and stop the run when the render itself fails.
+# Render a fixture, and stop the run when the render itself fails. A fixture
+# is a file, or a directory that holds a project.
 # $1 fixture base name. $2 target format.
 render() {
-	if ! quarto render "${work_dir}/$1.qmd" --to "$2" --quiet >"${work_dir}/$1.log" 2>&1; then
+	local target="${work_dir}/$1.qmd"
+	if [ -d "${work_dir}/$1" ]; then
+		target="${work_dir}/$1"
+	fi
+	if ! quarto render "${target}" --to "$2" --quiet >"${work_dir}/$1.log" 2>&1; then
 		printf 'FAIL  %s: the render failed\n' "$1"
 		tail -n 20 "${work_dir}/$1.log"
 		exit 1
@@ -538,6 +543,24 @@ else
 		"four windows, two of them named bash, in language-not-first.typ"
 fi
 
+# ============================================================================
+# Quarto's own code blocks are left alone
+# ============================================================================
+
+# The front matter of a chapter becomes a quarto-title-block code block.
+book_dir="${work_dir}/book"
+cp -R "${tests_dir}/fixtures/book" "${book_dir}"
+cp -R "${work_dir}/_extensions" "${book_dir}/_extensions"
+render book typst
+book_typ="${book_dir}/index.typ"
+if [ "$(count_typst_windows "${book_typ}")" -eq 1 ] &&
+	! grep -q 'quarto-title-block' "${book_typ}"; then
+	report pass "book: the chapter title block gets no window"
+else
+	report fail "book: the chapter title block gets no window" \
+		"one window, for the r block, and no quarto-title-block in index.typ"
+fi
+
 # ============================================================================
 
 printf '\n%s passed, %s failed\n' "${passed}" "${failed}"