Fix {{< placeholder >}} shortcode failing on non-SVG output (#14724)

The `{{< placeholder >}}` shortcode fetched a rasterized PNG from the
`svg2png.deno.dev` service for every non-SVG format. That service was
permanently retired and now returns 404, so placeholders failed to
render — a broken image on html, a hard LaTeX abort on pdf.

Rasterize locally with the already-bundled Typst binary instead: the
shortcode writes its SVG plus a one-line Typst wrapper to a temp dir,
runs `typst compile --format png`, and returns a base64 PNG data URI.
No network, no new bundled assets. On failure it aborts loudly rather
than substituting placeholder text (that silent substitution was the
original bug). The `format=svg` and Typst-output paths are unchanged.

A contract test pins the assumption the fix relies on — that Typst
renders the dimension label using its portable embedded fonts.

Fixes #14722

Author: cderv

news/changelog-1.10.md

@@ -139,3 +139,4 @@ All changes included in 1.10:
 - ([#14595](https://github.com/quarto-dev/quarto-cli/issues/14595)): Fix reload preview in code-server environment
 - ([#14669](https://github.com/quarto-dev/quarto-cli/issues/14669)): Fix markdown output being deleted when `output-file` has an `.html` extension and an html format is paired with a markdown format.
 - ([#14687](https://github.com/quarto-dev/quarto-cli/issues/14687)): Fix SCSS color-variable export (`--quarto-scss-export-*`) being silently skipped when a theme rule places a declaration on the same line as the opening brace with no space after the colon (e.g. `.example {width:100px;}`).
+- ([#14722](https://github.com/quarto-dev/quarto-cli/issues/14722)): Fix `{{< placeholder >}}` shortcode failing to render on non-SVG formats after an external image service was retired; placeholders now render locally with no network access.

src/resources/extensions/quarto/placeholder/placeholder.lua

@@ -25,21 +25,33 @@ return {
     if output_format == "svg" then
       result = svg64
     else
-      local pcallresult, mt, contents = pcall(function()
-        local mt, contents = pandoc.mediabag.fetch("https://svg2png.deno.dev/" .. svg64)
-        return mt, contents
+      local ok, contents = pcall(function()
+        return pandoc.system.with_temporary_directory('placeholder', function(tmpdir)
+          local svg_in = pandoc.path.join({tmpdir, 'in.svg'})
+          local typ_in = pandoc.path.join({tmpdir, 'in.typ'})
+          local png_out = pandoc.path.join({tmpdir, 'out.png'})
+          local sf = assert(io.open(svg_in, 'wb'))
+          sf:write(svg)
+          sf:close()
+          local tf = assert(io.open(typ_in, 'wb'))
+          tf:write('#set page(width: auto, height: auto, margin: 0pt)\n#image("in.svg")\n')
+          tf:close()
+          pandoc.pipe(quarto.paths.typst(), {
+            'compile', '--root', tmpdir, '--format', 'png', '--ppi', '96',
+            '--ignore-system-fonts', typ_in, png_out
+          }, '')
+          local pf = assert(io.open(png_out, 'rb'))
+          local data = pf:read('*a')
+          pf:close()
+          return data
+        end)
       end)
-      if not pcallresult then
-        error("Error rendering placeholder")
-        error(contents)
-        return pandoc.Str("Error rendering placeholder")
+      if not ok or contents == nil or contents == '' then
+        -- Local, offline rasterization: a failure is a real bug, not a flake. Fail loudly.
+        -- Do NOT substitute other content (that silent substitution was the original bug).
+        fatal('placeholder: failed to rasterize SVG to PNG via typst (' .. tostring(contents) .. ')')
       end
-      if mt ~= "image/png" then
-        error("Expected image/png but got " .. mt)
-        error(contents)
-        return pandoc.Str("Error rendering placeholder")
-      end
-      result = "data:" .. mt .. ";base64," .. quarto.base64.encode(contents)
+      result = 'data:image/png;base64,' .. quarto.base64.encode(contents)
     end
 
     if context == "text" then

tests/docs/smoke-all/2024/05/14/placeholder-test.qmd

@@ -1,5 +1,13 @@
 ---
 format: html
+_quarto:
+  tests:
+    html:
+      # The placeholder shortcode must never leak its error string into the
+      # output as image content (regression: svg2png.deno.dev sunset, #14722).
+      ensureFileRegexMatches:
+        - ['data:image/png;base64']          # png placeholders rasterize locally via typst
+        - ['Error rendering placeholder']     # and never leak the error text
 ---
 
 ::: {#fig-placeholder-test}

tests/smoke/render/placeholder-typst-text.test.ts

@@ -0,0 +1,61 @@
+/*
+ * placeholder-typst-text.test.ts
+ *
+ * The `placeholder` shortcode rasterizes its generated SVG to PNG with the
+ * bundled Typst binary (#14722). That path only works if Typst renders the
+ * dimension label text using its embedded fonts (we pass
+ * `--ignore-system-fonts`). This contract test pins that assumption: a
+ * labelled SVG must produce a materially larger PNG than a blank one — if
+ * Typst silently dropped the text, both would be the same blank rectangle.
+ *
+ * Copyright (C) 2026 Posit Software, PBC
+ */
+
+import { assert } from "testing/asserts";
+import { join } from "path";
+import { unitTest } from "../../test.ts";
+import { typstBinaryPath } from "../../../src/core/typst.ts";
+
+async function renderPng(label: string, dir: string): Promise<Uint8Array> {
+  const svg =
+    `<svg width="120" height="60" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 120 60"><rect width="120" height="60" fill="#ddd"/><text x="50%" y="50%" font-family="sans-serif" font-size="12" fill="#000" text-anchor="middle">${label}</text></svg>`;
+  await Deno.writeTextFile(join(dir, "in.svg"), svg);
+  await Deno.writeTextFile(
+    join(dir, "in.typ"),
+    `#set page(width: auto, height: auto, margin: 0pt)\n#image("in.svg")\n`,
+  );
+  const png = join(dir, `${label.trim() || "blank"}.png`);
+  const { code } = await new Deno.Command(typstBinaryPath(), {
+    args: [
+      "compile",
+      "--root",
+      dir,
+      "--format",
+      "png",
+      "--ppi",
+      "96",
+      "--ignore-system-fonts",
+      join(dir, "in.typ"),
+      png,
+    ],
+  }).output();
+  assert(code === 0, "typst compile failed");
+  return await Deno.readFile(png);
+}
+
+unitTest("placeholder-typst-renders-label-text", async () => {
+  const dir = await Deno.makeTempDir();
+  try {
+    const withText = await renderPng("120 x 60", dir);
+    const blank = await renderPng(" ", dir);
+    assert(withText[0] === 0x89 && withText[1] === 0x50, "not a PNG");
+    // A rendered label yields a materially larger PNG than a blank rect; if
+    // Typst silently dropped the text, both would be the same blank rect.
+    assert(
+      withText.length > blank.length + 100,
+      `label did not render: ${withText.length}B vs blank ${blank.length}B`,
+    );
+  } finally {
+    await Deno.remove(dir, { recursive: true });
+  }
+});