🧜‍♀️ Support mermaid as a code block

.changeset/khaki-poems-hunt.md

@@ -0,0 +1,7 @@
+---
+'myst-transforms': patch
+'myst-cli': patch
+'mystmd': patch
+---
+
+Translate mermaid and math code blocks by default.

docs/diagrams.md

@@ -20,3 +20,7 @@ flowchart LR
   D <--> J[JATS]
 ```
 ````
+
+:::{note}
+Both GitHub and JupyterLab ([#101](https://github.com/jupyter/enhancement-proposals/pull/101)) support the translation of a code-block ` ```mermaid ` to a mermaid diagram directly, this can also be used by default in MyST.
+:::

packages/myst-transforms/src/basic.ts

@@ -8,15 +8,16 @@ import { admonitionBlockquoteTransform, admonitionHeadersTransform } from './adm
 import { blockMetadataTransform, blockNestingTransform } from './blocks.js';
 import { htmlIdsTransform } from './htmlIds.js';
 import { imageAltTextTransform } from './images.js';
-import { mathCodeBlockTransform, mathLabelTransform, mathNestingTransform } from './math.js';
+import { mathLabelTransform, mathNestingTransform } from './math.js';
 import { blockquoteTransform } from './blockquote.js';
+import { codeBlockToDirectiveTransform } from './code.js';
 
 export function basicTransformations(tree: Root, file: VFile) {
   // lifting roles and directives must happen before the mystTarget transformation
   liftMystDirectivesAndRolesTransform(tree);
   // Some specifics about the ordering are noted below
   captionParagraphTransform(tree);
-  mathCodeBlockTransform(tree, file);
+  codeBlockToDirectiveTransform(tree, file, { translate: ['math', 'mermaid'] });
   mathNestingTransform(tree, file);
   // Math labelling should happen before the target-transformation
   mathLabelTransform(tree, file);

packages/myst-transforms/src/code.ts

@@ -2,6 +2,7 @@ import type { Plugin } from 'unified';
 import type { Root } from 'mdast';
 import type { Code } from 'myst-spec';
 import { selectAll } from 'unist-util-select';
+import type { GenericNode } from 'myst-common';
 import { fileWarn } from 'myst-common';
 import type { VFile } from 'vfile';
 
@@ -30,3 +31,30 @@ export function codeTransform(mdast: Root, file: VFile, opts?: Options) {
 export const codePlugin: Plugin<[Options?], Root, Root> = (opts) => (tree, file) => {
   codeTransform(tree, file, opts);
 };
+
+type CodeBlockTransformOptions = {
+  translate: (string | { lang: string; directive?: string })[];
+};
+
+export function codeBlockToDirectiveTransform(
+  tree: Root,
+  file: VFile,
+  opts?: CodeBlockTransformOptions,
+) {
+  if (!opts || !opts.translate || opts.translate.length === 0) return;
+  const nodes = selectAll('code', tree) as Code[];
+  nodes.forEach((node) => {
+    if (!node.lang) return;
+    const res = opts.translate.find(
+      (t) => t === node.lang || (typeof t !== 'string' && t.lang === node.lang),
+    );
+    if (!res) return;
+    (node as GenericNode).type = typeof res === 'string' ? res : res.directive || res.lang;
+    delete node.lang;
+  });
+}
+
+export const codeBlockToDirectivePlugin: Plugin<[CodeBlockTransformOptions?], Root, Root> =
+  (opts) => (tree, file) => {
+    codeBlockToDirectiveTransform(tree, file, opts);
+  };

packages/myst-transforms/src/math.spec.ts

@@ -1,7 +1,8 @@
 import { describe, expect, test } from 'vitest';
 import { unified } from 'unified';
 import { VFile } from 'vfile';
-import { mathTransform, mathPlugin, mathNestingTransform, mathCodeBlockTransform } from './math';
+import { mathTransform, mathPlugin, mathNestingTransform } from './math';
+import { codeBlockToDirectiveTransform } from './code';
 
 const ARRAY_ALIGN = `\\begin{align*}
   L=
@@ -129,7 +130,7 @@ describe('Test math code block transformation', () => {
   test('Block paragraph', () => {
     const file = new VFile();
     const mdast = { children: [{ type: 'code', lang: 'math', value: 'Ax = b' }] } as any;
-    mathCodeBlockTransform(mdast, file);
+    codeBlockToDirectiveTransform(mdast, file, { translate: ['math'] });
     expect(mdast.children[0].type).toBe('math');
     expect(mdast.children[0].lang).toBeUndefined();
     expect(mdast.children[0].value).toBe('Ax = b');

packages/myst-transforms/src/math.ts

@@ -239,26 +239,13 @@ export function mathLabelTransform(tree: Root, file: VFile) {
   });
 }
 
-// eslint-disable-next-line @typescript-eslint/no-unused-vars
-export function mathCodeBlockTransform(tree: Root, file: VFile) {
-  const nodes = selectAll('code[lang="math"]', tree) as Code[];
-  nodes.forEach((node) => {
-    (node as unknown as Math).type = 'math';
-    delete node.lang;
-  });
-}
-
 export function mathTransform(tree: Root, file: VFile, opts?: Options) {
   const nodes = selectAll('math,inlineMath', tree) as (Math | InlineMath)[];
   nodes.forEach((node) => {
     renderEquation(file, node, opts);
   });
 }
 
-export const mathCodeBlockPlugin: Plugin<[], Root, Root> = () => (tree, file) => {
-  mathCodeBlockTransform(tree, file);
-};
-
 export const mathNestingPlugin: Plugin<[], Root, Root> = () => (tree, file) => {
   mathNestingTransform(tree, file);
 };