Merge pull request #4470 from mermaid-js/sidv/splitUnicode

Split formatted markdown strings with unicode support.

docs/config/usage.md

@@ -228,7 +228,7 @@ mermaid fully supports webpack. Here is a [working demo](https://github.com/merm
 
 The main idea of the API is to be able to call a render function with the graph definition as a string. The render function will render the graph and call a callback with the resulting SVG code. With this approach it is up to the site creator to fetch the graph definition from the site (perhaps from a textarea), render it and place the graph somewhere in the site.
 
-The example below show an outline of how this could be used. The example just logs the resulting SVG to the JavaScript console.
+The example below shows an example of how this could be used. The example just logs the resulting SVG to the JavaScript console.
 
 ```html
 <script type="module">

packages/mermaid/src/diagrams/class/classDiagramGrammar.spec.ts

@@ -1,16 +0,0 @@
-import { readFile } from 'node:fs/promises';
-import { fileURLToPath } from 'node:url';
-// @ts-ignore - no types
-import { LALRGenerator } from 'jison';
-
-const getAbsolutePath = (relativePath: string) => {
-  return fileURLToPath(new URL(relativePath, import.meta.url));
-};
-
-describe('class diagram grammar', function () {
-  it('should have no conflicts', async function () {
-    const grammarSource = await readFile(getAbsolutePath('./parser/classDiagram.jison'), 'utf8');
-    const grammarParser = new LALRGenerator(grammarSource, {});
-    expect(grammarParser.conflicts).toBe(0);
-  });
-});

packages/mermaid/src/rendering-util/createText.ts

@@ -1,31 +1,20 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+// @ts-nocheck TODO: Fix types
 import { log } from '../logger.js';
 import { decodeEntities } from '../mermaidAPI.js';
 import { markdownToHTML, markdownToLines } from '../rendering-util/handle-markdown-text.js';
-/**
+import { splitLineToFitWidth } from './splitText.js';
- * @param dom
+import { MarkdownLine, MarkdownWord } from './types.js';
- * @param styleFn
+
- */
 function applyStyle(dom, styleFn) {
   if (styleFn) {
     dom.attr('style', styleFn);
   }
 }
 
-/**
- * @param element
- * @param {any} node
- * @param width
- * @param classes
- * @param addBackground
- * @returns {SVGForeignObjectElement} Node
- */
 function addHtmlSpan(element, node, width, classes, addBackground = false) {
   const fo = element.append('foreignObject');
-  // const newEl = document.createElementNS('http://www.w3.org/2000/svg', 'foreignObject');
-  // const newEl = document.createElementNS('http://www.w3.org/2000/svg', 'foreignObject');
   const div = fo.append('xhtml:div');
-  // const div = body.append('div');
-  // const div = fo.append('div');
 
   const label = node.label;
   const labelClass = node.isNode ? 'nodeLabel' : 'edgeLabel';
@@ -64,12 +53,12 @@ function addHtmlSpan(element, node, width, classes, addBackground = false) {
 /**
  * Creates a tspan element with the specified attributes for text positioning.
  *
- * @param {object} textElement - The parent text element to append the tspan element.
+ * @param textElement - The parent text element to append the tspan element.
- * @param {number} lineIndex - The index of the current line in the structuredText array.
+ * @param lineIndex - The index of the current line in the structuredText array.
- * @param {number} lineHeight - The line height value for the text.
+ * @param lineHeight - The line height value for the text.
- * @returns {object} The created tspan element.
+ * @returns The created tspan element.
  */
-function createTspan(textElement, lineIndex, lineHeight) {
+function createTspan(textElement: any, lineIndex: number, lineHeight: number) {
   return textElement
     .append('tspan')
     .attr('class', 'text-outer-tspan')
@@ -78,17 +67,10 @@ function createTspan(textElement, lineIndex, lineHeight) {
     .attr('dy', lineHeight + 'em');
 }
 
-/**
+function computeWidthOfText(parentNode: any, lineHeight: number, line: MarkdownLine): number {
- * Compute the width of rendered text
- * @param {object} parentNode
- * @param {number} lineHeight
- * @param {string} text
- * @returns {number}
- */
-function computeWidthOfText(parentNode, lineHeight, text) {
   const testElement = parentNode.append('text');
   const testSpan = createTspan(testElement, 1, lineHeight);
-  updateTextContentAndStyles(testSpan, [{ content: text, type: 'normal' }]);
+  updateTextContentAndStyles(testSpan, line);
   const textLength = testSpan.node().getComputedTextLength();
   testElement.remove();
   return textLength;
@@ -98,59 +80,37 @@ function computeWidthOfText(parentNode, lineHeight, text) {
  * Creates a formatted text element by breaking lines and applying styles based on
  * the given structuredText.
  *
- * @param {number} width - The maximum allowed width of the text.
+ * @param width - The maximum allowed width of the text.
- * @param {object} g - The parent group element to append the formatted text.
+ * @param g - The parent group element to append the formatted text.
- * @param {Array} structuredText - The structured text data to format.
+ * @param structuredText - The structured text data to format.
- * @param addBackground
+ * @param addBackground - Whether to add a background to the text.
  */
-function createFormattedText(width, g, structuredText, addBackground = false) {
+function createFormattedText(
+  width: number,
+  g: any,
+  structuredText: MarkdownWord[][],
+  addBackground = false
+) {
   const lineHeight = 1.1;
   const labelGroup = g.append('g');
-  let bkg = labelGroup.insert('rect').attr('class', 'background');
+  const bkg = labelGroup.insert('rect').attr('class', 'background');
   const textElement = labelGroup.append('text').attr('y', '-10.1');
-  // .attr('dominant-baseline', 'middle')
-  // .attr('text-anchor', 'middle');
-  // .attr('text-anchor', 'middle');
   let lineIndex = 0;
-  structuredText.forEach((line) => {
+  for (const line of structuredText) {
     /**
      * Preprocess raw string content of line data
      * Creating an array of strings pre-split to satisfy width limit
      */
-    let fullStr = line.map((data) => data.content).join(' ');
+    const checkWidth = (line: MarkdownLine) =>
-    let tempStr = '';
+      computeWidthOfText(labelGroup, lineHeight, line) <= width;
-    let linesUnderWidth = [];
+    const linesUnderWidth = checkWidth(line) ? [line] : splitLineToFitWidth(line, checkWidth);
-    let prevIndex = 0;
-    if (computeWidthOfText(labelGroup, lineHeight, fullStr) <= width) {
-      linesUnderWidth.push(fullStr);
-    } else {
-      for (let i = 0; i <= fullStr.length; i++) {
-        tempStr = fullStr.slice(prevIndex, i);
-        log.info(tempStr, prevIndex, i);
-        if (computeWidthOfText(labelGroup, lineHeight, tempStr) > width) {
-          const subStr = fullStr.slice(prevIndex, i);
-          // Break at space if any
-          const lastSpaceIndex = subStr.lastIndexOf(' ');
-          if (lastSpaceIndex > -1) {
-            i = prevIndex + lastSpaceIndex + 1;
-          }
-          linesUnderWidth.push(fullStr.slice(prevIndex, i).trim());
-          prevIndex = i;
-          tempStr = null;
-        }
-      }
-      if (tempStr != null) {
-        linesUnderWidth.push(tempStr);
-      }
-    }
     /** Add each prepared line as a tspan to the parent node */
-    const preparedLines = linesUnderWidth.map((w) => ({ content: w, type: line.type }));
+    for (const preparedLine of linesUnderWidth) {
-    for (const preparedLine of preparedLines) {
+      const tspan = createTspan(textElement, lineIndex, lineHeight);
-      let tspan = createTspan(textElement, lineIndex, lineHeight);
+      updateTextContentAndStyles(tspan, preparedLine);
-      updateTextContentAndStyles(tspan, [preparedLine]);
       lineIndex++;
     }
-  });
+  }
   if (addBackground) {
     const bbox = textElement.node().getBBox();
     const padding = 2;
@@ -159,7 +119,6 @@ function createFormattedText(width, g, structuredText, addBackground = false) {
       .attr('y', -padding)
       .attr('width', bbox.width + 2 * padding)
       .attr('height', bbox.height + 2 * padding);
-    // .style('fill', 'red');
 
     return labelGroup.node();
   } else {
@@ -171,40 +130,27 @@ function createFormattedText(width, g, structuredText, addBackground = false) {
  * Updates the text content and styles of the given tspan element based on the
  * provided wrappedLine data.
  *
- * @param {object} tspan - The tspan element to update.
+ * @param tspan - The tspan element to update.
- * @param {Array} wrappedLine - The line data to apply to the tspan element.
+ * @param wrappedLine - The line data to apply to the tspan element.
  */
-function updateTextContentAndStyles(tspan, wrappedLine) {
+function updateTextContentAndStyles(tspan: any, wrappedLine: MarkdownWord[]) {
   tspan.text('');
 
   wrappedLine.forEach((word, index) => {
     const innerTspan = tspan
       .append('tspan')
-      .attr('font-style', word.type === 'em' ? 'italic' : 'normal')
+      .attr('font-style', word.type === 'emphasis' ? 'italic' : 'normal')
       .attr('class', 'text-inner-tspan')
       .attr('font-weight', word.type === 'strong' ? 'bold' : 'normal');
-    const special = ['"', "'", '.', ',', ':', ';', '!', '?', '(', ')', '[', ']', '{', '}'];
     if (index === 0) {
       innerTspan.text(word.content);
     } else {
+      // TODO: check what joiner to use.
       innerTspan.text(' ' + word.content);
     }
   });
 }
 
-/**
- *
- * @param el
- * @param {*} text
- * @param {*} param1
- * @param root0
- * @param root0.style
- * @param root0.isTitle
- * @param root0.classes
- * @param root0.useHtmlLabels
- * @param root0.isNode
- * @returns
- */
 // Note when using from flowcharts converting the API isNode means classes should be set accordingly. When using htmlLabels => to sett classes to'nodeLabel' when isNode=true otherwise 'edgeLabel'
 // When not using htmlLabels => to set classes to 'title-row' when isTitle=true otherwise 'title-row'
 export const createText = (
@@ -234,7 +180,7 @@ export const createText = (
       ),
       labelStyle: style.replace('fill:', 'color:'),
     };
-    let vertexNode = addHtmlSpan(el, node, width, classes, addSvgBackground);
+    const vertexNode = addHtmlSpan(el, node, width, classes, addSvgBackground);
     return vertexNode;
   } else {
     const structuredText = markdownToLines(text);

packages/mermaid/src/rendering-util/handle-markdown-text.spec.ts

@@ -152,9 +152,8 @@ test('markdownToLines - Only italic formatting', () => {
 });
 
 it('markdownToLines - Mixed formatting', () => {
-  const input = `*Italic* and **bold** formatting`;
+  let input = `*Italic* and **bold** formatting`;
-
+  let expected = [
-  const expectedOutput = [
     [
       { content: 'Italic', type: 'emphasis' },
       { content: 'and', type: 'normal' },
@@ -162,9 +161,21 @@ it('markdownToLines - Mixed formatting', () => {
       { content: 'formatting', type: 'normal' },
     ],
   ];
+  expect(markdownToLines(input)).toEqual(expected);
 
-  const output = markdownToLines(input);
+  input = `*Italic with space* and **bold ws** formatting`;
-  expect(output).toEqual(expectedOutput);
+  expected = [
+    [
+      { content: 'Italic', type: 'emphasis' },
+      { content: 'with', type: 'emphasis' },
+      { content: 'space', type: 'emphasis' },
+      { content: 'and', type: 'normal' },
+      { content: 'bold', type: 'strong' },
+      { content: 'ws', type: 'strong' },
+      { content: 'formatting', type: 'normal' },
+    ],
+  ];
+  expect(markdownToLines(input)).toEqual(expected);
 });
 
 it('markdownToLines - Mixed formatting', () => {

packages/mermaid/src/rendering-util/handle-markdown-text.ts

@@ -1,11 +1,13 @@
+import type { Content } from 'mdast';
 import { fromMarkdown } from 'mdast-util-from-markdown';
 import { dedent } from 'ts-dedent';
+import { MarkdownLine, MarkdownWordType } from './types.js';
 
 /**
- * @param {string} markdown markdown to process
+ * @param markdown - markdown to process
- * @returns {string} processed markdown
+ * @returns processed markdown
  */
-function preprocessMarkdown(markdown) {
+function preprocessMarkdown(markdown: string): string {
   // Replace multiple newlines with a single newline
   const withoutMultipleNewlines = markdown.replace(/\n{2,}/g, '\n');
   // Remove extra spaces at the beginning of each line
@@ -14,19 +16,15 @@ function preprocessMarkdown(markdown) {
 }
 
 /**
- * @param {string} markdown markdown to split into lines
+ * @param markdown - markdown to split into lines
  */
-export function markdownToLines(markdown) {
+export function markdownToLines(markdown: string): MarkdownLine[] {
   const preprocessedMarkdown = preprocessMarkdown(markdown);
   const { children } = fromMarkdown(preprocessedMarkdown);
-  const lines = [[]];
+  const lines: MarkdownLine[] = [[]];
   let currentLine = 0;
 
-  /**
+  function processNode(node: Content, parentType: MarkdownWordType = 'normal') {
-   * @param {import('mdast').Content} node
-   * @param {string} [parentType]
-   */
-  function processNode(node, parentType = 'normal') {
     if (node.type === 'text') {
       const textLines = node.value.split('\n');
       textLines.forEach((textLine, index) => {
@@ -58,17 +56,10 @@ export function markdownToLines(markdown) {
   return lines;
 }
 
-/**
+export function markdownToHTML(markdown: string) {
- * @param {string} markdown markdown to convert to HTML
- * @returns {string} HTML
- */
-export function markdownToHTML(markdown) {
   const { children } = fromMarkdown(markdown);
 
-  /**
+  function output(node: Content): string {
-   * @param {import('mdast').Content} node
-   */
-  function output(node) {
     if (node.type === 'text') {
       return node.value.replace(/\n/g, '<br/>');
     } else if (node.type === 'strong') {

packages/mermaid/src/rendering-util/splitText.spec.ts

@@ -0,0 +1,147 @@
+import { splitTextToChars, splitLineToFitWidth, splitLineToWords } from './splitText.js';
+import { describe, it, expect, vi } from 'vitest';
+import type { CheckFitFunction, MarkdownLine, MarkdownWordType } from './types.js';
+
+describe('when Intl.Segmenter is available', () => {
+  describe('splitText', () => {
+    it.each([
+      { str: '', split: [] },
+      { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', split: ['🏳️‍⚧️', '🏳️‍🌈', '👩🏾‍❤️‍👨🏻'] },
+      { str: 'ok', split: ['o', 'k'] },
+      { str: 'abc', split: ['a', 'b', 'c'] },
+    ])('should split $str into graphemes', ({ str, split }: { str: string; split: string[] }) => {
+      expect(splitTextToChars(str)).toEqual(split);
+    });
+  });
+
+  describe('split lines', () => {
+    it('should create valid checkFit function', () => {
+      const checkFit5 = createCheckFn(5);
+      expect(checkFit5([{ content: 'hello', type: 'normal' }])).toBe(true);
+      expect(
+        checkFit5([
+          { content: 'hello', type: 'normal' },
+          { content: 'world', type: 'normal' },
+        ])
+      ).toBe(false);
+      const checkFit1 = createCheckFn(1);
+      expect(checkFit1([{ content: 'A', type: 'normal' }])).toBe(true);
+      expect(checkFit1([{ content: '🏳️‍⚧️', type: 'normal' }])).toBe(true);
+      expect(checkFit1([{ content: '🏳️‍⚧️🏳️‍⚧️', type: 'normal' }])).toBe(false);
+    });
+
+    it.each([
+      // empty string
+      { str: 'hello world', width: 7, split: ['hello', 'world'] },
+      // width > full line
+      { str: 'hello world', width: 20, split: ['hello world'] },
+      // width < individual word
+      { str: 'hello world', width: 3, split: ['hel', 'lo', 'wor', 'ld'] },
+      { str: 'hello 12 world', width: 4, split: ['hell', 'o 12', 'worl', 'd'] },
+      { str: 'hello  1 2 world', width: 4, split: ['hell', 'o  1', '2', 'worl', 'd'] },
+      { str: 'hello  1 2 world', width: 6, split: ['hello', '  1 2', 'world'] },
+      // width = 0, impossible, so split into individual characters
+      { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', width: 0, split: ['🏳️‍⚧️', '🏳️‍🌈', '👩🏾‍❤️‍👨🏻'] },
+      { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', width: 1, split: ['🏳️‍⚧️', '🏳️‍🌈', '👩🏾‍❤️‍👨🏻'] },
+      { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', width: 2, split: ['🏳️‍⚧️🏳️‍🌈', '👩🏾‍❤️‍👨🏻'] },
+      { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', width: 3, split: ['🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻'] },
+      { str: '中文中', width: 1, split: ['中', '文', '中'] },
+      { str: '中文中', width: 2, split: ['中文', '中'] },
+      { str: '中文中', width: 3, split: ['中文中'] },
+      { str: 'Flag 🏳️‍⚧️ this 🏳️‍🌈', width: 6, split: ['Flag 🏳️‍⚧️', 'this 🏳️‍🌈'] },
+    ])(
+      'should split $str into lines of $width characters',
+      ({ str, split, width }: { str: string; width: number; split: string[] }) => {
+        const checkFn = createCheckFn(width);
+        const line: MarkdownLine = getLineFromString(str);
+        expect(splitLineToFitWidth(line, checkFn)).toEqual(
+          split.map((str) => getLineFromString(str))
+        );
+      }
+    );
+  });
+});
+
+/**
+ * Intl.Segmenter is not supported in Firefox yet,
+ * see https://bugzilla.mozilla.org/show_bug.cgi?id=1423593
+ */
+describe('when Intl.Segmenter is not available', () => {
+  beforeAll(() => {
+    vi.stubGlobal('Intl', { Segmenter: undefined });
+  });
+  afterAll(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it.each([
+    { str: '', split: [] },
+    {
+      str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻',
+      split: [...'🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻'],
+    },
+    { str: 'ok', split: ['o', 'k'] },
+    { str: 'abc', split: ['a', 'b', 'c'] },
+  ])('should split $str into characters', ({ str, split }: { str: string; split: string[] }) => {
+    expect(splitTextToChars(str)).toEqual(split);
+  });
+
+  it.each([
+    // empty string
+    { str: 'hello world', width: 7, split: ['hello', 'world'] },
+    // width > full line
+    { str: 'hello world', width: 20, split: ['hello world'] },
+    // width < individual word
+    { str: 'hello world', width: 3, split: ['hel', 'lo', 'wor', 'ld'] },
+    { str: 'hello 12 world', width: 4, split: ['hell', 'o 12', 'worl', 'd'] },
+    { str: 'hello  1 2 world', width: 4, split: ['hell', 'o  1', '2', 'worl', 'd'] },
+    { str: 'hello  1 2 world', width: 6, split: ['hello', ' 1 2', 'world'] },
+    // width = 0, impossible, so split into individual characters
+    { str: 'abc', width: 0, split: ['a', 'b', 'c'] },
+    { str: '🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻', width: 1, split: [...'🏳️‍⚧️🏳️‍🌈👩🏾‍❤️‍👨🏻'] },
+    { str: '中文中', width: 1, split: ['中', '文', '中'] },
+    { str: '中文中', width: 2, split: ['中文', '中'] },
+    { str: '中文中', width: 3, split: ['中文中'] },
+  ])(
+    'should split $str into lines of $width characters',
+    ({ str, split, width }: { str: string; width: number; split: string[] }) => {
+      const checkFn = createCheckFn(width);
+      const line: MarkdownLine = getLineFromString(str);
+      expect(splitLineToFitWidth(line, checkFn)).toEqual(
+        split.map((str) => getLineFromString(str))
+      );
+    }
+  );
+});
+
+it('should handle strings with newlines', () => {
+  const checkFn: CheckFitFunction = createCheckFn(6);
+  const str = `Flag
+  🏳️‍⚧️ this 🏳️‍🌈`;
+  expect(() =>
+    splitLineToFitWidth(getLineFromString(str), checkFn)
+  ).toThrowErrorMatchingInlineSnapshot(
+    '"splitLineToFitWidth does not support newlines in the line"'
+  );
+});
+
+const getLineFromString = (str: string, type: MarkdownWordType = 'normal'): MarkdownLine => {
+  return splitLineToWords(str).map((content) => ({
+    content,
+    type,
+  }));
+};
+
+/**
+ * Creates a checkFunction for a given width
+ * @param width - width of characters to fit in a line
+ * @returns checkFunction
+ */
+const createCheckFn = (width: number): CheckFitFunction => {
+  return (text: MarkdownLine) => {
+    // Join all words into a single string
+    const joinedContent = text.map((w) => w.content).join('');
+    const characters = splitTextToChars(joinedContent);
+    return characters.length <= width;
+  };
+};

packages/mermaid/src/rendering-util/splitText.ts

@@ -0,0 +1,135 @@
+import type { CheckFitFunction, MarkdownLine, MarkdownWord, MarkdownWordType } from './types.js';
+
+/**
+ * Splits a string into graphemes if available, otherwise characters.
+ */
+export function splitTextToChars(text: string): string[] {
+  if (Intl.Segmenter) {
+    return [...new Intl.Segmenter().segment(text)].map((s) => s.segment);
+  }
+  return [...text];
+}
+
+/**
+ * Splits a string into words by using `Intl.Segmenter` if available, or splitting by ' '.
+ * `Intl.Segmenter` uses the default locale, which might be different across browsers.
+ */
+export function splitLineToWords(text: string): string[] {
+  if (Intl.Segmenter) {
+    return [...new Intl.Segmenter(undefined, { granularity: 'word' }).segment(text)].map(
+      (s) => s.segment
+    );
+  }
+  // Split by ' ' removes the ' 's from the result.
+  const words = text.split(' ');
+  // Add the ' 's back to the result.
+  const wordsWithSpaces = words.flatMap((s) => [s, ' ']).filter((s) => s);
+  // Remove last space.
+  wordsWithSpaces.pop();
+  return wordsWithSpaces;
+}
+
+/**
+ * Splits a word into two parts, the first part fits the width and the remaining part.
+ * @param checkFit - Function to check if word fits
+ * @param word - Word to split
+ * @returns [first part of word that fits, rest of word]
+ */
+export function splitWordToFitWidth(
+  checkFit: CheckFitFunction,
+  word: MarkdownWord
+): [MarkdownWord, MarkdownWord] {
+  const characters = splitTextToChars(word.content);
+  return splitWordToFitWidthRecursion(checkFit, [], characters, word.type);
+}
+
+function splitWordToFitWidthRecursion(
+  checkFit: CheckFitFunction,
+  usedChars: string[],
+  remainingChars: string[],
+  type: MarkdownWordType
+): [MarkdownWord, MarkdownWord] {
+  if (remainingChars.length === 0) {
+    return [
+      { content: usedChars.join(''), type },
+      { content: '', type },
+    ];
+  }
+  const [nextChar, ...rest] = remainingChars;
+  const newWord = [...usedChars, nextChar];
+  if (checkFit([{ content: newWord.join(''), type }])) {
+    return splitWordToFitWidthRecursion(checkFit, newWord, rest, type);
+  }
+  if (usedChars.length === 0 && nextChar) {
+    // If the first character does not fit, split it anyway
+    usedChars.push(nextChar);
+    remainingChars.shift();
+  }
+  return [
+    { content: usedChars.join(''), type },
+    { content: remainingChars.join(''), type },
+  ];
+}
+
+/**
+ * Splits a line into multiple lines that satisfy the checkFit function.
+ * @param line - Line to split
+ * @param checkFit - Function to check if line fits
+ * @returns Array of lines that fit
+ */
+export function splitLineToFitWidth(
+  line: MarkdownLine,
+  checkFit: CheckFitFunction
+): MarkdownLine[] {
+  if (line.some(({ content }) => content.includes('\n'))) {
+    throw new Error('splitLineToFitWidth does not support newlines in the line');
+  }
+  return splitLineToFitWidthRecursion(line, checkFit);
+}
+
+function splitLineToFitWidthRecursion(
+  words: MarkdownWord[],
+  checkFit: CheckFitFunction,
+  lines: MarkdownLine[] = [],
+  newLine: MarkdownLine = []
+): MarkdownLine[] {
+  // Return if there is nothing left to split
+  if (words.length === 0) {
+    // If there is a new line, add it to the lines
+    if (newLine.length > 0) {
+      lines.push(newLine);
+    }
+    return lines.length > 0 ? lines : [];
+  }
+  let joiner = '';
+  if (words[0].content === ' ') {
+    joiner = ' ';
+    words.shift();
+  }
+  const nextWord: MarkdownWord = words.shift() ?? { content: ' ', type: 'normal' };
+  const lineWithNextWord: MarkdownLine = [...newLine];
+  if (joiner !== '') {
+    lineWithNextWord.push({ content: joiner, type: 'normal' });
+  }
+  lineWithNextWord.push(nextWord);
+
+  if (checkFit(lineWithNextWord)) {
+    // nextWord fits, so we can add it to the new line and continue
+    return splitLineToFitWidthRecursion(words, checkFit, lines, lineWithNextWord);
+  }
+
+  // nextWord doesn't fit, so we need to split it
+  if (newLine.length > 0) {
+    // There was text in newLine, so add it to lines and push nextWord back into words.
+    lines.push(newLine);
+    words.unshift(nextWord);
+  } else if (nextWord.content) {
+    // There was no text in newLine, so we need to split nextWord
+    const [line, rest] = splitWordToFitWidth(checkFit, nextWord);
+    lines.push([line]);
+    if (rest.content) {
+      words.unshift(rest);
+    }
+  }
+  return splitLineToFitWidthRecursion(words, checkFit, lines);
+}

packages/mermaid/src/rendering-util/types.d.ts

@@ -0,0 +1,8 @@
+export type MarkdownWordType = 'normal' | 'strong' | 'emphasis';
+export interface MarkdownWord {
+  content: string;
+  type: MarkdownWordType;
+}
+export type MarkdownLine = MarkdownWord[];
+/** Returns `true` if the line fits a constraint (e.g. it's under 𝑛 chars) */
+export type CheckFitFunction = (text: MarkdownLine) => boolean;

tsconfig.json

@@ -14,7 +14,7 @@
     "target": "ES6" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
     "lib": [
       "DOM",
-      "ES2021"
+      "ES2022"
     ] /* Specify a set of bundled library declaration files that describe the target runtime environment. */,
     // "jsx": "preserve",                                /* Specify what JSX code is generated. */
     // "experimentalDecorators": true,                   /* Enable experimental support for TC39 stage 2 draft decorators. */