perf: skip AST struct conversion when rendering Markdown - #404
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`MDEx.to_html/2` spent most of its time translating the AST between the `MDEx.*` and `MDExNative.Comrak.*` namespaces, twice per render. Two changes, closes #395: * `MDEx.ComrakConverter` resolved the target module per node with `Module.split/1` + `Module.safe_concat/1`, then rebuilt the struct field by field. Both namespaces declare the same fields, so the table is now expanded into function clauses at compile time and a node converts by swapping `__struct__`. * Rendering HTML or XML from Markdown with no pipeline steps and no codefence renderers no longer builds an Elixir AST at all — the NIF renders the source directly and both translation passes disappear. 26 KB inline-heavy document, 50 iterations: | path | before | after | | ----------------------------- | -------: | ------: | | `to_html!/2` on Markdown | 31.73 ms | 1.24 ms | | `to_html!/1` with a step (AST) | 31.58 ms | 7.98 ms | `MDEx.to_xml/2` on a document now emits the root `sourcepos` attribute under `render: [sourcepos: true]`, matching what it already emitted when called with a Markdown binary.
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe rendering pipeline now accepts format atoms and bypasses AST translation for eligible HTML and XML renders. Documents expose buffered Markdown for this path. Comrak struct conversion now uses compile-time mappings and shape-aware recursive conversion. ChangesRendering and conversion
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to HTML and XML rendering can bypass AST conversion when safe, while transformed and AST-dependent paths retain document processing. No current merge-blocking risk is identified. Sequence Diagram(s)sequenceDiagram
participant Caller
participant MDEx
participant Document
participant Comrak
Caller->>MDEx: request HTML or XML
MDEx->>Document: read unparsed Markdown
Document-->>MDEx: return buffered Markdown
MDEx->>Comrak: render Markdown directly
Comrak-->>Caller: return HTML or XML
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches 💡 2📝 Generate docstrings 💡
🛠️ Fix failing CI checks 💡
🧪 Generate unit tests (beta)
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In `@test/mdex/comrak_converter_test.exs`:
- Line 122: Replace the Application.load call for :mdex_native with
Application.ensure_loaded, matching its successful :ok result so repeated
application loading remains idempotent before module discovery.
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lib/mdex.exlib/mdex/comrak_converter.exlib/mdex/document.extest/mdex/comrak_converter_test.exstest/mdex/html_format_test.exstest/mdex/xml_format_test.exs
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`Application.load/1` always returned `{:error, {:already_loaded, :mdex_native}}`
here, since `mdex_native` is a started dependency. The result was discarded, so
the test worked, but the call was misleading — use `Application.ensure_loaded/1`,
which is idempotent, and assert on its result.
The round trip also passed vacuously if module discovery came back empty or
partial, which is exactly when this guard matters. It now asserts the discovered
set covers `@nodes` first, and skips modules that aren't structs.
1 participant
Closes #395.
MDEx.to_html/2spent most of its time translating the AST between theMDEx.*andMDExNative.Comrak.*namespaces, twice per render. Two independent changes:Compile-time translation table
MDEx.ComrakConverterresolved each node's target module at runtime withModule.split/1+Module.safe_concat/1, then rebuilt the struct field by field withMap.from_struct/1+Map.new/2+struct/2.Both namespaces declare the same fields — the only difference is the namespace — so the table is now expanded into function clauses at compile time and a node converts by swapping
__struct__. Only:nodes,:sourceposand:attrsrecurse.Documentkeeps a dedicated clause becauseMDEx.Documentalso carries pipeline state (:options,:steps, ...). A node decoded by a mismatchedmdex_nativefalls back tostruct/2, so the existing missing-field behaviour is preserved.Skipping the round trip
Rendering HTML or XML from Markdown with no pipeline steps and no codefence renderers doesn't need an Elixir AST, so the NIF now renders the source directly and both translation passes disappear. The AST path is still taken for pipeline steps, codefence renderers, already-parsed nodes, streaming/fragment completion, halted documents and
to_markdown/2.Results
26 KB inline-heavy document, 50 iterations:
MDExNativeto_html!/2on Markdownto_html!/1with a step (AST path)Other shapes on the Markdown path: prose-heavy 28 KB 3.43 → 0.33 ms, typical README 1.2 KB 0.62 → 0.15 ms.
Behaviour change
MDEx.to_xml/2on a document now emits the rootsourceposattribute underrender: [sourcepos: true].MDEx.to_xml/2on a Markdown binary already emitted it — the AST round trip dropped it becauseflush_buffer/2keeps only the parsed nodes. The two entry points now agree; covered by a new test.Verification
mix credo --strictclean, no compiler warnings.sourceposabove.MDExNative.Comrakdefines (catches a node missing from the table), direct render matches the pipeline, steps and pre-parsed documents still take the AST path.Summary by CodeRabbit