Crate merman 

Headless, parity-focused Mermaid parsing and rendering in Rust.

merman is the public Rust facade for the project. It re-exports merman_core for detection, parsing, metadata, semantic JSON, and typed render models, then adds optional convenience modules for SVG, raster, and terminal text output.

The compatibility target is Mermaid @11.15.0. Upstream Mermaid behavior is treated as the specification, including cases where the browser implementation is surprising. The root README and docs/alignment/STATUS.md document the current parity matrix, deferred residuals, and release gates.

Choosing an API

Goal	Feature	Start with
Parse Mermaid or produce semantic JSON	none	Engine and ParseOptions
Render Mermaid-like SVG	render	merman::render::HeadlessRenderer
Prepare SVG for usvg / resvg / raster export	render	HeadlessRenderer::render_svg_resvg_safe_sync
Render terminal-friendly text	ascii	merman::ascii::HeadlessAsciiRenderer
Render PNG, JPG, or PDF from Rust	raster	HeadlessRenderer::render_png_sync and render::raster::RasterOptions

If you already know the diagram type, use the *_with_type_sync methods on Engine to skip detection. If you need lower-level layout or SVG pipeline control, use the re-exported types under merman::render or depend on merman-render directly.

Features

• render: layout plus SVG rendering through merman::render.
• ascii: ASCII/Unicode text rendering through merman::ascii.
• raster: PNG/JPG/PDF output through merman::render::raster; this implies render.
• ratex-math: pure-Rust math label rendering for the SVG path; this implies render.

The default feature set is intentionally empty so parser-only users do not pull in layout, SVG, raster, or text-output dependencies.

SVG quickstart

use merman::render::HeadlessRenderer;

let renderer = HeadlessRenderer::new().with_diagram_id("readme-example");
let svg = renderer
    .render_svg_sync("flowchart TD\nA[Start] --> B[Done]")?
    .expect("diagram detected");

println!("{svg}");

A fresh HeadlessRenderer keeps the Mermaid parity SVG contract for HeadlessRenderer::render_svg_sync. Calling with_host_theme or with_svg_pipeline installs a renderer-owned output pipeline for that method. Use HeadlessRenderer::render_svg_readable_sync when browser <foreignObject> labels may need readable <text> fallbacks, and HeadlessRenderer::render_svg_resvg_safe_sync when the output will be consumed by usvg, resvg, or the built-in raster helpers.

ASCII quickstart

use merman::ascii::{AsciiRenderOptions, HeadlessAsciiRenderer};

let renderer = HeadlessAsciiRenderer::new()
    .with_strict_parsing()
    .with_ascii_options(AsciiRenderOptions::unicode());
let text = renderer
    .render_ascii_sync("sequenceDiagram\nA->>B: Hello")?
    .expect("diagram detected");

println!("{text}");

Text output is intentionally terminal-native rather than SVG-derived. The currently supported public subset covers flowchart/graph, sequenceDiagram, classDiagram, erDiagram, and xychart.

Raster output

The raster feature renders SVG through the resvg-safe pipeline before conversion. PNG and JPG use a default pixmap budget to avoid accidental huge allocations from very large Mermaid viewBox values. For UI previews, pass a visible target box through RasterOptions::with_fit_to and use RasterOptions::with_scale for device-pixel ratio.

Modules

ascii

baseline

Active upstream Mermaid baseline metadata.

common

common_db

config

detect

diagram

diagrams

entities

error

generated

geom

models

preprocess

render

sanitize

time

utils

Structs

Detector

One diagram detector entry.

DetectorRegistry

Ordered registry that detects Mermaid diagram types.

DiagramRegistry

Registry for semantic JSON parsers keyed by Mermaid diagram type id.

Engine

Headless Mermaid parser engine.

MermaidConfig

ParseMetadata

Metadata extracted before semantic diagram parsing.

ParseOptions

Parser behavior switches shared by metadata, semantic JSON, and typed render-model parsing.

ParsedDiagram

Parsed diagram metadata plus the Mermaid-compatible semantic JSON model.

ParsedDiagramRender

Parsed diagram metadata plus a typed render model.

PreprocessResult

RenderDiagramRegistry

Registry for typed render-model parsers keyed by Mermaid diagram type id.

Enums

Error

RenderSemanticModel

Typed semantic model used by the headless renderer.

Constants

MAX_DIAGRAM_NESTING_DEPTH

Maximum nested diagram/include depth accepted by recursive parsers.

Functions

preprocess_diagram

preprocess_diagram_with_known_type

supported_diagrams

Returns supported diagram metadata names for binding and host capability discovery.

supported_host_theme_presets

Returns built-in host/editor theme preset names.

supported_themes

Returns Mermaid theme names supported by the pinned baseline.

Type Aliases

DiagramSemanticParser

Parser used by the semantic JSON path for one Mermaid diagram family.

RenderSemanticParser

Parser used by the typed render-model path for one Mermaid diagram family.

Result