fix(monaco): support high contrast themes in shikiToMonaco

[Yashsingh045]

Description

This PR adds support for high-contrast themes in shikiToMonaco.

Previously, shikiToMonaco would assign vs or vs-dark as the base theme based on the theme type (light or dark). This caused issues with high-contrast themes (like GitHub High Contrast) where the selection foreground color would not be visible because Monaco only applies editor.selectionForeground when the base theme is hc-black or hc-light.

I have added a new themes option to ShikiToMonacoOptions that allows users to explicitly specify the theme type, including hc and hc-light.

Fixes #1081

Changes

• Updated ShikiToMonacoOptions to include a themes property for overrides.
• Updated textmateThemeToMonacoTheme to accept an options object and determine the correct base theme (hc-black, hc-light, vs, or vs-dark) based on the configuration.
• Updated shikiToMonaco to pass these options down.

Verification

• Added a reproduction test case in packages/monaco/test/high-contrast.test.ts which verifies that providing the hc type correctly sets the base theme to hc-black.
• Verified that existing tests in packages/monaco/test/repro.test.ts still pass.

Usage Example

shikiToMonaco(highlighter, monaco, {
  themes: {
    'github-dark-high-contrast': {
      type: 'hc' // Sets base to 'hc-black'
    }
  }
})

[netlify]

✅ Deploy Preview for shiki-next ready!

Name	Link
🔨 Latest commit	742a9e0
🔍 Latest deploy log	https://app.netlify.com/projects/shiki-next/deploys/693013a4951cc10008b75289
😎 Deploy Preview	https://deploy-preview-1185--shiki-next.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[netlify]

✅ Deploy Preview for shiki-matsu ready!

Name	Link
🔨 Latest commit	742a9e0
🔍 Latest deploy log	https://app.netlify.com/projects/shiki-matsu/deploys/693013a4951cc10008b75287
😎 Deploy Preview	https://deploy-preview-1185--shiki-matsu.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.20%. Comparing base (61c87e8) to head (742a9e0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1185   +/-   ##
=======================================
  Coverage   95.20%   95.20%           
=======================================
  Files          92       92           
  Lines        7922     7922           
  Branches     1689     1689           
=======================================
  Hits         7542     7542           
  Misses        374      374           
  Partials        6        6           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[antfu]

I wonder if #1099 would be easier and simple. Do you see any other cases that need more customizations?

[Yashsingh045]

hey @antfu ,

I checked #1099. The auto-detection based on theme name is definitely simpler for the common ‘happy path’, but relying only on string matching can be limiting for more advanced setups.

For example, any high-contrast theme that doesn’t follow the exact naming convention — such as my-accessible-theme or company-contrast-theme — wouldn’t be recognized correctly. Since #1099 doesn’t provide an override mechanism, users would have no way to handle these cases.

My PR #1185 introduces a themes option that acts as an explicit escape hatch. It lets users define high-contrast behavior for any theme, not just the ones that match predefined naming patterns. This keeps shikiToMonaco simple for typical use cases while still offering flexibility for custom or non-standard themes.

[Yashsingh045]

Hi @antfu ,
Just checking in — please let me know if there’s anything more I should address in this PR.
A review when possible would be greatly appreciated.