[plugin:@tailwindcss/vite:generate:serve] Invalid code point 15530851 error after tailwind v3 -> v4 upgrade

[Inglan]

I have a SvelteKit site and use shadcn-svelte. I just decided to update to v4, as shadcn-svelte has released new components compatible with v4.

I followed the instructions in their upgrade guide and got to Step 2 - Verify the upgrade and this is where it showed this error:

[plugin:@tailwindcss/vite:generate:serve] Invalid code point 15530851

/Users/ingowolf/Projects/ProjectName/src/app.css

RangeError: Invalid code point 15530851
    at Function.fromCodePoint (<anonymous>)
    at file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/tailwindcss@4.1.10/node_modules/tailwindcss/dist/chunk-E562WLSY.mjs:1:4667
    at String.replace (<anonymous>)
    at ge (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/tailwindcss@4.1.10/node_modules/tailwindcss/dist/chunk-E562WLSY.mjs:1:4596)
    at Be.markUsedVariable (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/tailwindcss@4.1.10/node_modules/tailwindcss/dist/chunk-E562WLSY.mjs:1:6719)
    at Object.build (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/tailwindcss@4.1.10/node_modules/tailwindcss/dist/chunk-E562WLSY.mjs:35:1565)
    at Object.build (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/tailwindcss@4.1.10/node_modules/tailwindcss/dist/chunk-E562WLSY.mjs:35:1949)
    at C.generate (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/@tailwindcss+vite@4.1.10_vite@6.3.5_jiti@2.4.2_lightningcss@1.30.1_yaml@2.7.0_/node_modules/@tailwindcss/vite/dist/index.mjs:1:4941)
    at async TransformPluginContext.transform (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/@tailwindcss+vite@4.1.10_vite@6.3.5_jiti@2.4.2_lightningcss@1.30.1_yaml@2.7.0_/node_modules/@tailwindcss/vite/dist/index.mjs:1:1949)
    at async EnvironmentPluginContainer.transform (file:///Users/ingowolf/Projects/ProjectName/node_modules/.pnpm/vite@6.3.5_jiti@2.4.2_lightningcss@1.30.1_yaml@2.7.0/node_modules/vite/dist/node/chunks/dep-DBxKXgDP.js:42294:18

[wongjn]

Check if you have some binary or binary-like files in your project that have a file extension that does not appear in this list. If so, try ignoring them. Otherwise, consider providing a git repo that reproduces the unexpected behavior.

[Inglan]

This is probably why. I will do this when I have the time, thanks!

[bl-ue]

15530851 is the decimal version of 0xecfb63. Try searching for \ecfb63 in all the files in your project.

In my case (Invalid code point 5171233, which is decimal for 0x4ee821), the substring \4ee821 appeared as part of a UUID in a .md file. Ignoring the directory containing that markdown file solved it.

markUsedVariable calls unescape, which calls String.fromCodePoint on a string found using the regex /\\([\dA-Fa-f]{1,6}[\t\n\f\r ]?|[\S\s])/g, which in this case means a backslash followed by 1-6 hex characters.