Decorations API throws TypeError when decorating last index

[timothycohen]

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• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.

Describe the bug

Thanks for the project! I'm running into an undefined access bug preventing highlighting of the final index when using the decorations API. Looks like normalizePosition adds an invalid decoration (line is lines.length) and therefore const lineEl = lines[line]; in applyLineSection is undefined. I can submit a test and PR within the next couple days if it's still open.

Basic Reproduction

import { createHighlighter } from 'shiki';

const highlighterCore = await createHighlighter({ langs: ['ts'], themes: ['nord'] });

function highlight(str: string, start: number, end: number) {
	return highlighterCore
		.codeToHtml(str, {
			lang: 'ts',
			theme: 'nord',
			decorations: [{ start, end, properties: { ['data-wrap']: '' } }],
		})
}

// ✅ Add `data-wrap` to `.line` around `a`:
highlight(`a\nbcd`, 0, 1);

// ✅ Add a `data-wrap` span after `a` in first `.line`:
highlight(`a\nbcd`, 1, 1);

// ✅ Add `data-wrap` around `bc` in second `.line`:
highlight(`a\nbcd`, 2, 4);

// ❌ Expect to add `data-wrap` to `.line` around `bcd`, but throws TypeError
highlight(`a\nbcd`, 2, 5);

// ❌ Expect to add `data-wrap` after `bcd` in second `.line`, but throws TypeError
highlight(`a\nbcd`, 5, 5);

Error Log

file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:1022
                const children = lineEl.children.slice(startIndex, endIndex);
                                        ^

TypeError: Cannot read properties of undefined (reading 'children')
    at applyLineSection (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:1022:41)
    at Object.code (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:1066:21)
    at tokensToHast (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:1215:43)
    at codeToHast (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:1113:12)
    at codeToHtml (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:4685:25)
    at Object.codeToHtml (file:///Users/~/shiki-error/node_modules/.pnpm/@shikijs+core@1.11.0/node_modules/@shikijs/core/dist/index.mjs:5605:40)
    at highlight (/Users/~/shiki-error/src/index.ts:9:4)
    at <anonymous> (/Users/~/shiki-error/src/index.ts:22:13)

Node.js v20.14.0

Reproduction

https://stackblitz.com/edit/stackblitz-starters-w5wlgw

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests