Internal compiler error: let directive at invalid position.

[CropWatchDevelopment]

Describe the bug

Getting a build time error:

Internal compiler error: let directive at invalid position. Please report this to https://github.com/sveltejs/svelte/issues
  Plugin: vite-plugin-svelte
  File: /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53
  25 |      <li
  26 |        class={cls(
  27 |          typeof theme.li === 'string' ? theme.li : theme.li?.(node),
     |                             ^
  28 |          typeof classes.li === 'string' ? classes.li : classes.li?.(node)
  29 |        )}

Reproduction

See this repo for an example.
Clone -> Run pnpm install -> cd into packages/svelte-ux -> pnpm dev
Experiance the fun!

Logs

/home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53 Internal compiler error: let directive at invalid position. Please report this to https://github.com/sveltejs/svelte/issues
/home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53 Internal compiler error: let directive at invalid position. Please report this to https://github.com/sveltejs/svelte/issues (x2)
11:25:34 AM [vite-plugin-svelte] /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/ToggleOption.svelte:34:0 A11y: Non-interactive element <label> should not be assigned mouse or keyboard event listeners.
11:25:34 AM [vite] Internal server error: /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53 Internal compiler error: let directive at invalid position. Please report this to https://github.com/sveltejs/svelte/issues
  Plugin: vite-plugin-svelte
  File: /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53
  25 |      <li
  26 |        class={cls(
  27 |          typeof theme.li === 'string' ? theme.li : theme.li?.(node),
     |                             ^
  28 |          typeof classes.li === 'string' ? classes.li : classes.li?.(node)
  29 |        )}
      at error (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/errors.js:569:8)
      at LetDirective (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:2766:4)
      at next (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:106:21)
      at _ (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/scope.js:666:4)
      at visit (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:100:13)
      at Object.visit (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:86:20)
      at serialize_inline_component (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:748:66)
      at SvelteSelf (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:2730:21)
      at next (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:106:21)
      at _ (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/scope.js:666:4)
11:25:36 AM [vite] Internal server error: /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53 Internal compiler error: let directive at invalid position. Please report this to https://github.com/sveltejs/svelte/issues
  Plugin: vite-plugin-svelte
  File: /home/kevin/source/repos/opensource/svelte-ux/packages/svelte-ux/src/lib/components/TreeList.svelte:25:53
  25 |      <li
  26 |        class={cls(
  27 |          typeof theme.li === 'string' ? theme.li : theme.li?.(node),
     |                             ^
  28 |          typeof classes.li === 'string' ? classes.li : classes.li?.(node)
  29 |        )}
      at error (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/errors.js:569:8)
      at LetDirective (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:2766:4)
      at next (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:106:21)
      at _ (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/scope.js:666:4)
      at visit (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:100:13)
      at Object.visit (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:86:20)
      at serialize_inline_component (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:748:66)
      at SvelteSelf (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/3-transform/client/visitors/template.js:2730:21)
      at next (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/zimmerframe@1.1.0/node_modules/zimmerframe/src/walk.js:106:21)
      at _ (file:///home/kevin/source/repos/opensource/svelte-ux/node_modules/.pnpm/svelte@5.0.0-next.15/node_modules/svelte/src/compiler/phases/scope.js:666:4) (x2)

System Info

Linux Mint
Brave Browser

Severity

blocking an upgrade

[dummdidumm]

See which repo? There's no link to a repository.
Please just copy-paste the full content of that TreeList.svelte file into this issue, that should be enough.

[7nik]

I believe this is a simplified version.

[techniq]

Was coming here to open this issue, and I see it was already reported. Here is a minimal reproduction REPL (and working Svelte 4 REPL, although it looks like @Rich-Harris already has a PR fix 🎉.

Btw, the original TreeList was in Svelte UX