Very slow in dev mode

[ruizdiazever]

Astro Info

Astro                    v5.1.3
Node                     v22.9.0
System                   macOS (arm64)
Package Manager          pnpm
Output                   server
Adapter                  @astrojs/node
Integrations             @astrojs/svelte
                         @astrojs/sitemap
                         @astrojs/mdx
                         @astrojs/tailwind
                         paraglide
                         astro-icon

If this issue only occurs in one browser, which browser is a problem?

Chrome, Safari, Firefox

Describe the Bug

Since my migration to astro 5 I have had a very high slowness in dev mode.
Only happen in dev mode in local, in a container work normal and in build mode too.

Where happen?

• macOS Sequoia 15.2 (local)
• WSL in Windows

Image example:

What's the expected result?

Normal refresh timing in dev mode

Link to minimal example

https://github.com/ruizdiazever/astro-svelte-demo

[ematipico]

It seems that the cause of the slowness is Header. I couldn't go deeper than that. If you can't provide a minimal reproduction, I suggest asking for support on our Discord server.

[github-actions]

Hello @ruizdiazever. Please provide a minimal reproduction using a GitHub repository or StackBlitz. Issues marked with needs repro will be closed if they have no activity within 3 days.

[ruizdiazever]

https://discord.com/channels/830184174198718474/1318629701505388644

[ascorbic]

Could you make the repro more minimal. We really need you to remove things until you can see where the issue disappears, or (better) start from an empty starter and add just the parts needed to reproduce it. As it stands, that site has a lot of stuff in there which make it hard for us to diagnose the source of the issue.

[ruizdiazever]

I will work on it, thanks.

[ruizdiazever]

Setting everything to client:only fix the problem, ruizdiazever/astro-svelte-demo@4f6829d

I rule out that it is something related to shadcn-svelte or Svelte since another person has the same problem without using Svelte

[ascorbic]

Are you importing any big UI or icon libraries? Modules that use barrel file exports can cause this sort of slowdown.

[ruizdiazever]

The problem only appears in Astro 5, in 4 this did not happen with the same UI and icon libraries!

[ascorbic]

I get that. Astro 5 also upgraded Vite to 6 which changed some things there. We have another issue looking at that. My point is that those kind of big barrel exports are a bad pattern in any case, and will always have a negative effect on Vite, particularly in dev. If that is the case here then it's a simple workaround (use subpath imports) that will avoid the current issue and make it even faster if we get a fix for that too.

[ruizdiazever]

The problem is basically due to how they are importing the Lucide icons (the one that appears in the official documentation), if I do it the way I clarify it does not happen.

https://stackblitz.com/~/github.com/raau-design/minimal?file=src/components/header/toggleDarkMode.svelte

https://github.com/raau-design/minimal/blob/main/src/components/header/toggleDarkMode.svelte

[kaishin]

Thanks @ruizdiazever, your solution worked for me as well.