Decoration API

[octref]

Offer a decoration API that allows marking specific ranges with:

• bg color
• font settings
• text decorations
• links

This is easy to use programmatically.
The hard problem is how should the original Markdown look like.

[octref]

Use cases. Applying these effects for a list of ranges. No range that spans multi line.

• Use italic for a specific range
• Use underline for a specific range
• Mark a range as link
• Give a range a background color

I'm thinking along these lines:

```js [[line | text or range | style]]
console.log('shiki');
```

• Line: A 0-based line number
• Text: The text to match. For example, log.
• Range: Start-End. For example, log is 8-11. Use this if text is ambiguous.
• Style:
  • i: italic
  • u: underline
  • http(s?)://example.org. If the style begins with http:// or https://, apply link effect, which shows underline on hover and open URL in new tab if clicked
  • #aabbcc. If the style begins with #, parse it as color.

So it could look like:

```js [[0 | log | #ff7B08], [0 | 7-8 | u], [0 | 'shiki' | https://shiki.matsu.io/]]
console.log('shiki');
```

What do you think, @atinux?

Also @ulivz I'd appreciate it a lot if you can give some feedback since you are leading Vuepress development now. Think Shiki is already better than highlightjs / prism and I'd want to make it a good highlighter for Vuepress too 😉

[EldoranDev]

Hi, are there currently any plans to actually implement this feature ?

[octref]

I wanted to gather some feedback before proceeding, because @atinux asked for this. But it seems he is busy. I'll ask again.

[wesbos]

Would love to see this : )

[Ir1d]

hi @octref , any plans to bring these features in? They look amazing

[orta]

I wonder if we make the highlighting API be consistent with gatsby-remark-prismjs - https://github.com/andrewbranch/gatsby-remark-vscode#line-highlighting

[octref]

Thinking about something like this API below. How each markdown parser would like to integrate with the API is up to them.
@EldoranDev @jlkiri @stefanprobst @Enter-tainer I see each of you have written a remark + shiki plugin — would the API below enable you do what https://github.com/andrewbranch/gatsby-remark-vscode is doing?

interface BaseLineDecoration {
  /**
   * The line to apply decoration to.
   * Line is 0 based.
   */
  line: number
}

/**
 * Render line with specified background color
 */
export interface LineBgColorDecoration extends BaseLineDecoration {
  /**
   * 3/6/8 digit hex code like `#fff` or color like `cadetblue`.
   */
  bgColor: string
}

/**
 * Render line with line number
 */
export interface LineNumberDecoration extends BaseLineDecoration {
  /**
   * Line number such as `1` or `01`
   */
  lineNumber: string
}

/**
 * A decoration applied to a line
 */
export type LineDecoration = LineBgColorDecoration | LineNumberDecoration

interface BaseTokensDecoration {
  /**
   * The range that includes all tokens. Only tokens that fully
   * fall into the range will be matched.
   * Multi-line is not supported.
   * Line is 0 based.
   * `startIndex` is inclusive and `endIndex` not inclusive.
   */
  range: {
    line: number
    startIndex: number
    endIndex: number
  }
}

/**
 * Render matched tokens with `<a>` tag
 *
 * Cannot overlap with other link decorations.
 */
export interface TokensLinkDecoration extends BaseTokensDecoration {
  /**
   * `href` value of the link
   */
  link: string
}

/**
 * Render matched tokens with specified font style
 */
export interface TokensFontStyleDecoration extends BaseTokensDecoration {
  /**
   * The font style
   */
  fontStyle: FontStyle
}

/**
 * Render matched tokens with specified background color
 */
export interface TokensBgColorDecoration extends BaseTokensDecoration {
  /**
   * 3/6/8 digit hex code like `#fff` or color like `cadetblue`.
   */
  bgColor: string
}

/**
 * A decoration applied to tokens in the matched range
 */
export type TokensDecoration =
  | TokensLinkDecoration
  | TokensFontStyleDecoration
  | TokensBgColorDecoration

export interface HtmlRendererOptions {
  langId?: string
  fg?: string
  bg?: string

  /**
   * Decorations applied to lines
   */
  lineDecorations?: LineDecoration[]

  /**
   * Decorations applied to tokens
   */
  tokensDecorations?: TokensDecoration[]
}

[jlkiri]

@octref I haven't touched remark for a long time. If there is a way to get lines I want to highlight from remark, then yes, I would use that information for each code block and pass it to something like highlighter.codeToHtml (not to getHighlighter because it would then apply to every code block)

[orta]

For shiki-twoslash, I ended up re-using @andrewbranch's code-fencing syntax from gatsby-vscode-remark

https://github.com/microsoft/TypeScript-website/blob/54415373f08ef8d707c0dca799b7a454d56ec754/packages/shiki-twoslash/src/parseCodeFenceInfo.ts#L1

[muenzpraeger]

Can't we potentially solve this via #380?

[antfu]

I would suggest the core should not have an opinion on how code-fence meta string should be handled. Instead, allowing transformers to provide their own handling