remark-lint-fenced-code-flag

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[remark-lint][github-remark-lint] rule to warn when language flags of fenced code
are not used or used incorrectly.

* What is this?
* When should I use this?
* Presets
* Install
* Use
* API
* [unified().use(remarkLintFencedCodeFlag[, options])](#unifieduseremarklintfencedcodeflag-options)
* checkGithubLinguistFlag(value)
* CheckFlag
* Options
* Recommendation
* Examples
* Compatibility
* Contribute
* License

What is this?

This package checks the language flags of fenced code blocks,
whether they exist,
and optionally what values they hold.

Particularly,
it provides a check according to GitHub Linguist.
Which is what GitHub uses to highlight code.
So you can make sure that the language flags you use are recognized by
GitHub (or [starry-night][github-starry-night])

When should I use this?

You can use this package to check that the style of language flags of fenced
code blocks is consistent and known.

Presets

This plugin is included in the following presets:

| Preset | Options |
| - | - |
| remark-preset-lint-markdown-style-guide | { allowEmpty: false } |

Install

This package is [ESM only][github-gist-esm].
In Node.js (version 16+),
install with [npm][npm-install]:

``sh npm install remark-lint-fenced-code-flag`

In Deno with [esm.sh][esm-sh]:

`js import remarkLintFencedCodeFlag, {checkGithubLinguistFlag} from 'https://esm.sh/remark-lint-fenced-code-flag@4'`

In browsers with [esm.sh][esm-sh]:

`html`

`Use`

On the API:

`js import remarkLint from 'remark-lint' import remarkLintFencedCodeFlag from 'remark-lint-fenced-code-flag' import remarkParse from 'remark-parse' import remarkStringify from 'remark-stringify' import {read} from 'to-vfile' import {unified} from 'unified' import {reporter} from 'vfile-reporter'

const file = await read('example.md')

await unified() .use(remarkParse) .use(remarkLint) .use(remarkLintFencedCodeFlag) .use(remarkStringify) .process(file)

console.error(reporter(file))`

On the CLI:

`sh remark --frail --use remark-lint --use remark-lint-fenced-code-flag .`

On the CLI in a config file (here a package.json):

`diff … "remarkConfig": { "plugins": [ … "remark-lint", + "remark-lint-fenced-code-flag", … ] } …`

`API`

This package exports the identifier [checkGithubLinguistFlag][api-check-github-linguist-flag]. It exports the [TypeScript][typescript] types [CheckFlag][api-check-flag] and [Options][api-options]. The default export is [remarkLintFencedCodeFlag][api-remark-lint-fenced-code-flag].

`$3`

Warn when language flags of fenced code are not used.

###### Parameters

* options (Array, [CheckFlag][api-check-flag], or [Options][api-options], optional) — check, configuration, or flags to allow

###### Returns

Transform ([Transformer from unified][github-unified-transformer]).

`$3`

Check according to GitHub Linguist.

###### Parameters

* value (string) — language flag to check

###### Returns

Whether the flag is valid (undefined), or a message to warn about (string).

###### Returns

Transform ([Transformer from unified][github-unified-transformer]).

`$3`

Custom check (TypeScript type).

###### Parameters

* value (string) — language flag to check

###### Returns

Whether the flag is valid (undefined), or a message to warn about (string).

`$3`

Configuration (TypeScript type).

###### Fields

* allowEmpty (boolean, default: false) — allow language flags to be omitted *flags (Array, optional) — flags to allow, other flags will result in a warning

`Recommendation`

While omitting language flags is fine to signal that code is plain text, it could point to a mistake. It’s recommended to instead use a certain flag for plain text (such astxt) and to turn this rule on. If possible, stick with what is supported by GitHub.

`Examples`

##### ok.md

###### In

``markdown Some markdown:

`markdown

`Mercury`


###### Out
No messages.

##### not-ok.md

###### In

``markdown`mercury()```

###### Out

`text 1:1-3:4: Unexpected missing fenced code language flag in info string, expected keyword`

##### ok-allow-empty.md

When configured with { allowEmpty: true }.

###### In

``markdown`mercury()```

###### Out

No messages.

##### not-ok-allow-empty.md

When configured with { allowEmpty: false }.

###### In

``markdown`mercury()```

###### Out

`text 1:1-3:4: Unexpected missing fenced code language flag in info string, expected keyword`

##### ok-array.md

When configured with [ 'markdown' ].

###### In

``markdown`markdown

`Mercury`


###### Out
No messages.

##### ok-options.md

When configured with { flags: [ 'markdown' ] }.

###### In

``markdown`markdown

`Mercury`


###### Out
No messages.

##### not-ok-array.md

When configured with [ 'markdown' ].

###### In

``markdown`javascript mercury()```

###### Out

`text 1:1-3:4: Unexpected fenced code language flagjavascript in info string, expected markdown`

##### not-ok-long-array.md

When configured with [ 'javascript', 'markdown', 'mdx', 'typescript' ].

###### In

``markdown`html

`Mercury`


###### Out

`text 1:1-3:4: Unexpected fenced code language flaghtml in info string, expected javascript, markdown, mdx, …`

##### not-ok-options.md

When configured with '🌍'.

###### Out

`text 1:1: Unexpected value🌍 for options, expected array or object`

`Compatibility`

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line,remark-lint-fenced-code-flag@4, compatible with Node.js 16.

`Contribute`

See [contributing.md][github-dotfiles-contributing] in [remarkjs/.github][github-dotfiles-health] for ways to get started. See [support.md`][github-dotfiles-support] for ways to get help.

This project has a [code of conduct][github-dotfiles-coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.

License

[MIT][file-license] © [Titus Wormer][author]

[api-check-flag]: #checkflag

[api-check-github-linguist-flag]: #checkgithublinguistflagvalue

[api-options]: #options

[api-remark-lint-fenced-code-flag]: #unifieduseremarklintfencedcodeflag-options

[author]: https://wooorm.com

[badge-build-image]: https://github.com/remarkjs/remark-lint/workflows/main/badge.svg

[badge-build-url]: https://github.com/remarkjs/remark-lint/actions

[badge-chat-image]: https://img.shields.io/badge/chat-discussions-success.svg

[badge-chat-url]: https://github.com/remarkjs/remark/discussions

[badge-coverage-image]: https://img.shields.io/codecov/c/github/remarkjs/remark-lint.svg

[badge-coverage-url]: https://codecov.io/github/remarkjs/remark-lint

[badge-downloads-image]: https://img.shields.io/npm/dm/remark-lint-fenced-code-flag.svg

[badge-downloads-url]: https://www.npmjs.com/package/remark-lint-fenced-code-flag

[badge-funding-backers-image]: https://opencollective.com/unified/backers/badge.svg

[badge-funding-sponsors-image]: https://opencollective.com/unified/sponsors/badge.svg

[badge-funding-url]: https://opencollective.com/unified

[badge-size-image]: https://img.shields.io/bundlejs/size/remark-lint-fenced-code-flag

[badge-size-url]: https://bundlejs.com/?q=remark-lint-fenced-code-flag

[esm-sh]: https://esm.sh

[file-license]: https://github.com/remarkjs/remark-lint/blob/main/license

[github-dotfiles-coc]: https://github.com/remarkjs/.github/blob/main/code-of-conduct.md

[github-dotfiles-contributing]: https://github.com/remarkjs/.github/blob/main/contributing.md

[github-dotfiles-health]: https://github.com/remarkjs/.github

[github-dotfiles-support]: https://github.com/remarkjs/.github/blob/main/support.md

[github-gist-esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[github-remark-lint]: https://github.com/remarkjs/remark-lint

[github-starry-night]: https://github.com/wooorm/starry-night

[github-unified-transformer]: https://github.com/unifiedjs/unified#transformer

[npm-install]: https://docs.npmjs.com/cli/install

[typescript]: https://www.typescriptlang.org

remark-lint-fenced-code-flag

[remark-lint][github-remark-lint] rule to warn when language flags of fenced code
are not used or used incorrectly.

What is this?

This package checks the language flags of fenced code blocks,
whether they exist,
and optionally what values they hold.

When should I use this?

You can use this package to check that the style of language flags of fenced
code blocks is consistent and known.

Presets

This plugin is included in the following presets:

| Preset | Options |
| - | - |
| remark-preset-lint-markdown-style-guide | { allowEmpty: false } |

Install

This package is [ESM only][github-gist-esm].
In Node.js (version 16+),
install with [npm][npm-install]:

``sh npm install remark-lint-fenced-code-flag`

In Deno with [esm.sh][esm-sh]:

`js import remarkLintFencedCodeFlag, {checkGithubLinguistFlag} from 'https://esm.sh/remark-lint-fenced-code-flag@4'`

In browsers with [esm.sh][esm-sh]:

`html`

`Use`

On the API:

const file = await read('example.md')

await unified() .use(remarkParse) .use(remarkLint) .use(remarkLintFencedCodeFlag) .use(remarkStringify) .process(file)

console.error(reporter(file))`

On the CLI:

`sh remark --frail --use remark-lint --use remark-lint-fenced-code-flag .`

On the CLI in a config file (here a package.json):

`diff … "remarkConfig": { "plugins": [ … "remark-lint", + "remark-lint-fenced-code-flag", … ] } …`

`API`

`$3`

Warn when language flags of fenced code are not used.

###### Parameters

* options (Array, [CheckFlag][api-check-flag], or [Options][api-options], optional) — check, configuration, or flags to allow

###### Returns

Transform ([Transformer from unified][github-unified-transformer]).

`$3`

Check according to GitHub Linguist.

###### Parameters

* value (string) — language flag to check

###### Returns

Whether the flag is valid (undefined), or a message to warn about (string).

###### Returns

Transform ([Transformer from unified][github-unified-transformer]).

`$3`

Custom check (TypeScript type).

###### Parameters

* value (string) — language flag to check

###### Returns

Whether the flag is valid (undefined), or a message to warn about (string).

`$3`

Configuration (TypeScript type).

###### Fields

* allowEmpty (boolean, default: false) — allow language flags to be omitted *flags (Array, optional) — flags to allow, other flags will result in a warning

`Recommendation`

`Examples`

##### ok.md

###### In

``markdown Some markdown:

`markdown

`Mercury`


###### Out
No messages.

##### not-ok.md

###### In

``markdown`mercury()```

###### Out

`text 1:1-3:4: Unexpected missing fenced code language flag in info string, expected keyword`

##### ok-allow-empty.md

When configured with { allowEmpty: true }.

###### In

``markdown`mercury()```

###### Out

No messages.

##### not-ok-allow-empty.md

When configured with { allowEmpty: false }.

###### In

``markdown`mercury()```

###### Out

`text 1:1-3:4: Unexpected missing fenced code language flag in info string, expected keyword`

##### ok-array.md

When configured with [ 'markdown' ].

###### In

``markdown`markdown

`Mercury`


###### Out
No messages.

##### ok-options.md

When configured with { flags: [ 'markdown' ] }.

###### In

``markdown`markdown

`Mercury`


###### Out
No messages.

##### not-ok-array.md

When configured with [ 'markdown' ].

###### In

``markdown`javascript mercury()```

###### Out

`text 1:1-3:4: Unexpected fenced code language flagjavascript in info string, expected markdown`

##### not-ok-long-array.md

When configured with [ 'javascript', 'markdown', 'mdx', 'typescript' ].

###### In

``markdown`html

`Mercury`


###### Out