Vanilla (Parcel) Unreliable Behavior When index.html Under Other Path (for example, in src)

🐛 bug report

Description of the problem

Using the Parcel bundler, the index.html file cannot be renamed or moved.

If the file is under a different path / name other than /index.html directly in the root, then there is unusual half-working unreliable behavior.

You can see this in the following sandboxes:

1. Index under /index.html: https://codesandbox.io/s/frozen-public-vanilla-parcel-bug-index-in-root-03p3w

With the index.html file in the root, everything works normally, including HTML from the HTML file itself.

The original DOM innerHTML of the body is as expected.

2. Index under /src/index.html: https://codesandbox.io/s/frozen-public-vanilla-parcel-bug-index-in-src-lcrew

With the index.html file in the src folder, some things work properly (such as modifying the document with JavaScript), but the DOM innerHTML content of the body is not stable and also does not match that of the HTML file.

Sometimes it even has CodeSandbox metadata in it:

How has this issue affected you? What are you trying to accomplish?

I want to be able to move and rename the index.html file as I wish, such as moving it under src/index.html.

Your Environment

Reproduce the two linked CodeSandbox examples, comparing a root index.html with src/index.html and the reported body innerHTML. Trace how Parcel handles the HTML entry path and why the generated DOM differs. Done means a renamed or moved HTML entry behaves consistently and preserves its source body content.