[Webkit-unassigned] [Bug 205294] New: import.meta.url: baseURL for a module script should be response URL, not request URL

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=205294

            Bug ID: 205294
           Summary: import.meta.url: baseURL for a module script should be
                    response URL, not request URL
           Product: WebKit
           Version: Safari 13
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: justinfagnani at google.com

According to: https://html.spec.whatwg.org/multipage/webappapis.html#fetching-scripts:creating-a-module-script-2

The base URL for a module script should be the response URL, post any redirects. Currently Webkit is using the request URL.

This causes significant problems (and incompatibility with Firefox and Chrome) when there are redirects in the response for a module.

Imagine you are using something like `new URL('./foo.jpg', import.meta.url).href` to get the URL for an image relative to the main module of an NPM package. A CDN like unpkg.com will perform a redirect from `unpkg.com/foo` to the main module, ie: `unpkg.com/foo/index.js`. This causes there to be a difference in the image's URL depending on whether `import.meta.url` uses response or request URL. Response URL will give `unpkg.com/foo/foo.jpg` while request URL will give `unpkg.com/foo.jpg`.

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