Mermaid/Graphviz don't render in HTML export when "include highlighting" is off

[schuyler]

Summary

The HTML-export path has the same coupling that #533 fixed for the live preview: Mermaid and Graphviz diagram scripts are emitted only when highlighting is included, so exporting HTML with "include highlighting" unchecked produces a document where diagram fences stay as plain code blocks — no SVG, no error.

This is the follow-up deliberately scoped out of #533 / #540 (which fixed only the live-preview path in -[MPRenderer scripts]).

Root cause

In -[MPRenderer HTMLForExportWithStyles:highlighting:] (MacDown/Code/Document/MPRenderer.m), the Mermaid/Graphviz script inclusion is nested inside the if (withHighlighting) block:

if (withHighlighting)
{
    // ... prism scripts ...
    // mermaid
    if ([d rendererHasMermaid:self]) { ...mermaidScripts... }
    // graphviz
    if ([d rendererHasGraphviz:self]) { ...graphvizScripts... }
}

When withHighlighting is NO, the mermaid/graphviz scripts are never added to the exported page, so the diagrams never render.

Note this path is reachable independently of the live-preview setting: withHighlighting comes from the export panel's "include highlighting" checkbox (controller.highlightingIncluded in -[MPDocument exportHtml:]), which is only initialized from htmlSyntaxHighlighting and can be toggled per-export.

Why it's a separate change from #533

Unlike -[MPRenderer scripts], this method also uses withHighlighting to drive scriptsOption = MPAssetEmbedded (asset-embedding vs. linking) for a self-contained exported file. So hoisting the mermaid/graphviz blocks out of the gate needs to preserve the correct asset-embedding behavior for those scripts, which is why it wasn't folded into the focused live-preview fix.

Expected behavior

Exported HTML renders Mermaid and Graphviz diagrams based on their own toggles, regardless of whether "include highlighting" is selected at export time.

Notes on testing

The existing export-path tests in MacDownTests/MPRendererEdgeCaseTests.m (testRendererWithMermaidEnabled / testRendererWithGraphvizEnabled) only assert the produced HTML is non-nil — they don't check for script presence/absence, so they wouldn't currently catch this. A fix should add assertions that the diagram scripts are present in the exported HTML with withHighlighting = NO.

[schuyler]

Proceeding with the following interpretation of the requirements (reviewed by a second agent against the actual code). Corrections welcome on the PR.

Fix shape

In -[MPRenderer HTMLForExportWithStyles:highlighting:], this is a two-part coupling, not a simple hoist:

1. Hoist the rendererHasMermaid / rendererHasGraphviz script-append blocks out of the if (withHighlighting) gate into their own top-level if blocks.
2. Promote scriptsOption to MPAssetEmbedded when Mermaid or Graphviz is enabled — mirroring the existing MathJax branch. This is load-bearing: scriptsOption starts at MPAssetNone, and with highlighting off it would otherwise stay MPAssetNone, which makes MPGetHTML silently drop the scripts (nil template) even after hoisting.
3. Remove the now-duplicate appends still inside the withHighlighting block, so diagram scripts aren't emitted twice when highlighting is also on.

Export embeds assets (MPAssetEmbedded inlines the JS content in <script>…</script>), so exported files stay self-contained/portable — consistent with existing export behavior and what MathJax already does.

Scope

In: the export path only; both halves of the coupling; strengthened test coverage.
Out: the live-preview path (already fixed in #540); stylesheet/stylesOption behavior (no Mermaid/Graphviz CSS exists — the theme is JS-driven); highlighting/styles semantics (Prism stays gated on withHighlighting); MathJax (already correct, untouched).

Expected behavior (key configurations)

• highlighting off + mermaid on → mermaid script present, Prism absent
• highlighting off + graphviz on → graphviz script present, Prism absent
• highlighting off + both → both present, each once
• highlighting on + diagram(s) → diagram scripts present exactly once (no double-inclusion), Prism present
• neither diagram enabled → no diagram scripts
• withStyles on/off must not affect diagram-script emission

Testing approach (headless, via the mock delegate)

Tests drive -[MPRenderer HTMLForExportWithStyles:highlighting:] and assert on the returned HTML. Because export embeds (inlines) rather than links, assertions use inlined-content substrings, never filenames (filename assertions only work on the -render/MPAssetFullLink preview path):

• Mermaid present: mermaid.initialize( (occurs once in mermaid.init.js, absent from mermaid.min.js)
• Graphviz present / double-inclusion guard: function doGraphviz(engine) { (occurs exactly once in viz.init.js, absent from viz.js) — chosen over graphviz_engines/doGraphviz, which recur within the file and can't support an occurrence count
• Prism absence asserted in highlighting-off cases (always safe). New tests deliberately do not assert Prism presence — its embedded substring is version/submodule-fragile, and the highlighting-on regression is guarded by diagram-script no-duplication instead.

The two existing edge-case tests (testRendererWithMermaidEnabled / testRendererWithGraphvizEnabled) currently assert only XCTAssertNotNil — which is why this bug shipped undetected. They will be strengthened in place, with new tests added for the remaining configurations.

Open questions

None blocking. If MathJax can't be exercised cleanly through the existing mock infra, the MathJax-coexistence case may be reduced to a comment (the MathJax branch is already correct and unmodified) — this will be noted in the PR if it happens.

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Generated by Claude Code

[schuyler]

Opened #542 with the fix and tests — CI is green.

The export path (-[MPRenderer HTMLForExportWithStyles:highlighting:]) now renders Mermaid and Graphviz regardless of the "include highlighting" export option: the diagram blocks were hoisted out of the if (withHighlighting) gate, each promoting scriptsOption to MPAssetEmbedded (mirroring the MathJax branch). Tests cover the config matrix (highlighting off/on, both diagrams, no double-inclusion, disabled, withStyles:NO independence, MathJax coexistence).

One follow-up is noted on the PR for the maintainer: the diagram-hoisting logic is now duplicated between the preview (-scripts) and export methods and could be unified into a shared helper.

The PR is ready for review and merge.

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Generated by Claude Code