warnHandler not invoked prior to app.mount() due to null stack / instance reference

[smolgumball]

Version

3.2.27

Reproduction link

jsfiddle.net

Steps to reproduce

• Note logs in console
• Note comment on line 11 of JS source

What is expected?

warnHandler be invoked for all warnings, even if app is not yet instanced / mounted.

What is actually happening?

warnHandler is skipped and internal warn handler runs.

Potentially related:

#4479

[LinusBorg]

The warnHandler is meant to handle warnings from things happening in components, i.e. during render. it's not meant to catch this kind of warning, really. That's why it receives a vm as the second argument.

[smolgumball]

That makes sense, but I'd think that internal warn's shouldn't be issued outside the scope of a component if that's the case. Having a warnHandler override that doesn't override all uses of warn seems unintuitive.

Would it be possible for warnHandler to be invoked with alternative arguments in the case that a component instance is not yet spun up?

[michael42]

This also happens when rendering a component server-side using @vue/server-renderer. How can we get the warnings during SSR to fail the request or at least print them in the browser?

[hokkaido]

@LinusBorg The default warn handler does not follow that pattern tho, it allows for instance vue-router to create copious amounts of warnings outside of the mount cycle without any way to ignore them.