HMR Issue with Parcel 2.0.0 release

[lucaseverett]

Describe the bug
When using Parcel 2.0.0 final release, the root node is duplicated upon saving a file, rather than replacing it. For example, when using the Solid Parcel Starter, you'll see the following after saving a file.

Solid Parcel Starter

Solid Parcel Starter

To Reproduce

1. Download Solid Parcel Starter from https://gitlab.com/enom/solid-parcel-starter
2. npm i and npm run dev
3. Make a change to index.js and observe that the page refreshes in the browser as expected.
4. Stop server, then update parcel in package.json from "next" to "2.0.0."
5. npm i and npm run dev
6. Make a change to index.js and observe that the root node is duplicated rather than replaced

Expected behavior
Upon saving a file the page content should be replaced rather than duplicated.

Additional context
I'm not sure if this is a Parcel bug or something within Solid. It doesn't happen when using Parcel 2.0.0-rc.0. The default behavior of Parcel is to simply reload a page if HMR isn't explicitly called.

[ryansolid]

This starter doesn't seem to be even using Solid's HMR library Solid Refresh (or any custom one for that matter). I think Parcel's default behavior must be just re-run the JavaScript again without cleaning up after itself? Since this isn't using Solid's method of HMR I'm sort of leaning towards this being a Parcel thing. But maybe that is their intended functionality. You can't really do a reload without them literally reloading the browser page and if they aren't doing that well that's the problem.

[lucaseverett]

Thank you for the response. The default behavior of Parcel, according to docs and to discussions I found in their old GitHub Issues, is to do a window.location.reload unless module.hot is explicitly called. That was the behavior up until the 2.0.0 release, so there must have been some regression. I'm going to file an issue on the Parcel repo.

[ryansolid]

@lucaseverett Did this ever go anywhere? Did you create the issue with Parcel?

[lucaseverett]

I created an issue for it, but there hasn't been any action on it yet.

parcel-bundler/parcel#7171

[lxsmnsyc]

Must be an upstream issue. I tested the latest Parcel 2 with solid and solid-refresh@^0.3.0 and there shouldn't be any issues.

[lucaseverett]

Yes, it's a Parcel bug, and it was caused by a commit made on September 25. There are several open issues that all seem to be related to this bug.

I edited the hmr-runtime.js file and removed return true from the code in the commit referenced above, and that indeed fixed the issue. I don't know enough about how the hmr-runtime works to know what needs to be rewritten. At least the cause is known, though.

parcel-bundler/parcel#7307

[lucaseverett]

A PR was merged today to fix this issue. I tested the latest nightly and the issue no longer happens.

parcel-bundler/parcel#7514