Add support for `lang` directive

[ludelafo]

Hi Marp team!

I'm interested to use the hyphens CSS property as follow:

theme: gaia
style: |
    p {
        hyphens: auto;
    }

In order for this to work, I need to set the lang attribute.

marp-cli defines the argument lang in its options. When using the command-line tool as npx @marp-team/marp-cli@latest --lang en --pdf --output README.pdf README.md, the hyphens are correctly rendered.

I would like to add support for the lang directive in marp-vscode so the language of the document can be set:

theme: gaia
lang: en
style: |
    p {
        hyphens: auto;
    }

From my understanding of the codebase, the starting point would be https://github.com/marp-team/marp-vscode/blob/d9af184ed12b65bb28c0f328e250955d548ac1d1/src/directives/definitions.ts by adding a new directive such as:

  // Marp CLI metadata options
  createDirectiveInfo({
    name: 'lang',
    description: 'Set lang of the slide deck.',
    allowed: directiveAlwaysAllowed,
    providedBy: DirectiveProvidedBy.MarpCLI,
    type: DirectiveType.Global,
    details: 'https://github.com/marp-team/marp-cli#metadata', // Need to update the metadata as well
  }),

Would this feature be useful for marp-vscode? I would be glad to implement this feature if you are interested.

[yhatt]

If so, the starting point would be Marp CLI rather than Marp for VS Code. Could you create an Issue in the Marp CLI repository to propose implementing lang global directive? https://github.com/marp-team/marp-cli/issues

[ludelafo]

Thank you very much @yhatt!