Using export & then using decorator before the word "default" breaks SFC compilation.

[andrewbrennanfr]

Version

2.7.14

Reproduction link

https://stackblitz.com/edit/vitejs-vite-bctp3t?file=src%2FApp.vue

Steps to reproduce

• Export a const from a SFC.

• Use a vue-property-decorator with @Component & export your class component as default.

• Include the word "default" in a comment (for example).

• Your component is not built correctly - in my reproduction example, the props are not initialized as an object. (you can see there is also no console warning related to someString).

• Remove the word "default" from the comment & refresh the page - props will initialize correctly & you also have the expected console warning.

---

Looks very similar to several issues (such as this one & this one)

Apparently this has been fixed here.

However it fails to work for me when @babel/parser is upgraded beyond 7.19.6
🟢 Working use case with 7.19.6
🛑 Non-working use case with 7.20.0

---

After some debugging it seems that the method hasDefaultExport in vuejs/vue is the one that's broken for this case & the one in vuejs/core is working.
https://github.com/vuejs/vue/blob/main/packages/compiler-sfc/src/rewriteDefault.ts#L91-L93

This regex change here would cause some unit tests (for my use case) start to fail. And for me this regex is maybe too loose.

Here 👉 there's no default export, yet this regex is a match https://regex101.com/r/LmYL8l/1

What is expected?

I expect my component to be built correctly & to not have a comment impacting the behavior of my component.

What is actually happening?

When inspecting the compiled code - it looks to me that the @Component decorator here is just completely stripped in the outputted code.

---

🙈 I've probably mistakenly opened an issue on vue/core here

---

Workaround for me, is to override @babel/parser for @vue/sfc-compiler to be 7.19.6 and the problem disappears.

Removing the exported const/type/interface/etc from the SFC works around the issue.

Moving the exported const/interface/type/etc below the class component also works around the issue.

This issue is not isolated to only comments, but rather the presence of default.
Meaning, code such as @Prop({ type: String, required: false, default: '' }) is also breaking - as the word default here has the same impact.

💡 I've attempted a sort of "backport" of the changes from vue/core & added a test for my use case. It looks to work.
https://github.com/andrewbrennanfr/vue/commits/fix/rewriteDefault-decorator-parsing

[andrewbrennanfr]

Perhaps this could be a cleaner "fix" - making the regex's a bit more explicit?
andrewbrennanfr@e6e26fb

[gbalduzzi]

I'm seeing the same problem in vite. This was a very nasty bug to debug and discover.

Workaround for me, is to override @babel/parser for @vue/sfc-compiler to be 7.19.6 and the problem disappears.

Not sure how to accomplish the same result this with vite and @vitejs/plugin-vue2

I forced the babel parser to 7.19.6 with yarn add @babel/parser@7.19.6 but the issue persists

[andrewbrennanfr]

@gbalduzzi Not sure it's particularly to do with Vite. We use Vite also & still managed to work around it.
I don't know your specific setup, but not sure running yarn add @babel/parser@7.19.6 would necessarily fix it.
Adding something like:

"overrides": {
        "@vue/compiler-sfc": {
            "@babel/parser": "7.19.6"
        }
}

To our package.json definitely overrides @babel/parser & "fixes" the issue.

Bare in mind, our intention is that this is temporary. Upgrading to vue3 should resolve the issue properly

[gbalduzzi]

@andrewbrennanfr thank you, I can confirm this works.

Yes, this is a temporary solution for us too while we migrate to vue3