Eric Traut
9fcb1f5ed4
## Why Flowcharts with `<br>` tags in node labels previously fell back to source instead of rendering as terminal diagrams. ## What changed Render `<br>`, `<br/>`, and `<br />` as line breaks in quoted and unquoted flowchart node labels. Apply the 40-display-cell label limit per line and keep the decision marker on the first line. Continue rejecting other HTML, break tags in edge labels, and labels containing only breaks or whitespace. ## Testing Extend rendering snapshots across all four flowchart directions and cover per-line width limits and unsupported markup. Update TUI streaming tests to cover multiline rendering, resizing, source fallback, and preservation of the original source for copying. GitOrigin-RevId: 61f2a84c8bb161ac4a1c26ddaa0569f52bfea749
codex-mermaid
Standalone, bounded Mermaid text renderer.
It uses the existing unicode-width dependency; no Mermaid runtime or new external
production dependency is needed.
Supported subsets
| Family | Supported syntax |
|---|---|
flowchart, graph |
TD/TB (default), BT, LR, RL; rectangle [label], decision {label}, and stadium ([label]) nodes; solid -->/---/<--> and dashed -.->/-.-/<-.-> edges; pipe labels and spaced directed infix labels (-- text -->, -. text .->); & fan-out/fan-in, chains, branches, merges, loops |
sequenceDiagram |
Implicit participants, participant/actor, aliases, ->, ->>, -->, -->>, -x, --x, self-messages, Note over A[,B], nested loop/alt/opt/critical/break, one labeled else per alt |
stateDiagram-v2, stateDiagram |
Flat states, state "label" as ID, descriptions, directed transitions with optional labels, initial/final [*], direction declarations |
classDiagram |
class ID, multiline member bodies, ID : member, solid/dashed links, association, inheritance, composition, aggregation, dependency, realization, quoted endpoint cardinalities, relationship labels, direction declarations |
erDiagram |
Entities, multiline attribute bodies, type name [PK, FK, UK] ["comment"], all four endpoint cardinalities, identifying/non-identifying relationships, relationship labels, direction declarations |
Identifiers are ASCII letters followed by letters, digits, or underscores. Text
supports ordinary Unicode and CJK. Full-line %% comments and
semicolon-separated statements are supported outside flowchart labels, quoted
tokens, and class bodies. Sequence quotes are literal text; use newlines between
class members, whose semicolons remain text. Member/attribute bodies need a
separate statement for each opening brace, member, and closing brace (for
example class Order { followed by member lines and a final }). Class member
text is retained in one compartment, including visibility, signatures, and
return types. ER attribute types and names use the identifier grammar above.
Flowchart node and edge labels may be enclosed in double quotes. Literal
ampersands are supported in labels, as is printable punctuation after parsing.
Quotes protect flowchart label delimiters such as brackets, pipes, and
semicolons. Flowchart node labels support <br>, <br/>, and <br /> as
line breaks. Other HTML and entity escapes remain unsupported.
These are explicit subsets, not complete Mermaid compatibility. Compound states, flowchart subgraphs, other shapes, sequence activation and parallel fragments, styling, front matter, directives, other HTML, escapes, combining/zero-width characters, and ligatures with non-additive widths return errors. Callers should retain source on any error; the library never returns a partial diagram.
Layout and notation
Graph nodes appear in declaration/first-reference order, in the requested direction.
Each edge gets its own lane and endpoint positions. Crossings use ╪ and never
join routes. Decisions use ◇ inside a box; stadiums use rounded box corners. Horizontal layouts
reserve a text gutter for every endpoint, which can make connected graphs wide;
the caller receives TooWide if the complete output does not fit.
Class links use arrows into the referenced class, ◁/△ for inheritance/realization,
◆ for composition, and ◇ for aggregation. Endpoint cardinalities appear in
parentheses next to the appropriate class or entity. ER cardinalities are written
as 1, 0..1, 1..many, or 0..many. Solid ER links are identifying; dashed links
are non-identifying. Class members and ER keys/comments appear verbatim as readable
text, rather than renderer metadata.
Sequence messages retain chronological order. ->>/-->> use ▶/◀ arrowheads,
->/--> have no arrowhead, and -x/--x use a cross endpoint. Solid and dashed
strokes remain distinct. Lifelines crossed by a message use ┼; this is not a recipient.
Control fragments have nested frames and explicit branch labels. Notes span their
named participants. States use separate ● initial and ◎ final nodes.
Limits and evaluation
All inputs are limited to 16 KiB. Graphs allow 16 nodes, 24 edges (after expanding
& groups), and 16 members per node. Each & group allows at most 24 node references. Sequences allow 8 participants, 64 events (including fragment boundaries),
and 4 fragment levels. Labels are limited to 40 display cells per line; identifiers
are limited to 40 ASCII bytes. Rendered canvases are capped at 65,536 cells,
independent of the caller's maximum width. The library performs no I/O.
From codex-rs, preview a file, optionally specifying the available width:
cargo run -p codex-mermaid --example render -- 180 < diagram.mmd
Run just test -p codex-mermaid --lib. Coverage includes complex snapshots for every
family, relationship endpoints, all ER cardinalities, width/error bounds,
truncated input, and reconstruction of every edge in all 512 directed three-node
graphs in each of the four layout directions.
render_spans returns the same layout as lines of semantic Node, Edge, and
Text spans. Callers apply their own theme; the crate never emits ANSI escapes.