[@web/dev-server-import-maps] Support for external import maps about web HOT 5 OPEN

I've quickly patched the https://github.com/modernweb-dev/web/blob/master/packages/dev-server-import-maps/src/importMapsPlugin.ts#L121-L123 file, and it works!

      if (getAttribute(importMapScript, 'src')) {
-       throw new Error('Import maps with a "src" attribute are not yet supported.');
+       const importMapPath = getAttribute(importMapScript, 'src');
+       const content = fs.readFileSync(importMapPath, 'utf8');
+       setTextContent(importMapScript, content);
+       removeAttribute(importMapScript, 'src');
      }

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There might be a good reasons not to support src.

From MDN https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script/type/importmap

The src, async, nomodule, defer, crossorigin, integrity, and referrerpolicy attributes must not be specified.

Pay attention that src is specifically mention as not allowed.

At the same time, in the proposal I see the src being described in https://github.com/wicg/import-maps#import-map-processing

You can install an import map for your application using a <script> element, either inline or with a src="" attribute:

Is there actually a consensus about this feature?

In general we try not to add non-standard features, at least without a good confidence that they will become a standard and got enough support from browser vendors and other stakeholders. In this case I can imagine the src involves an extra HTTP call which must be a blocking request due to how essential this information is for the module resolution, so maybe that's why it's not implemented natively.

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See WICG/import-maps#235. @domenic wrote that external import maps will be implemented in Chromium, but can't give an ETA.

Import maps can be very large and generated by third-party tools. Inline them manually into HTML is a poor DX.

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Thanks for sharing this link, it does shed some light on this.
I quickly scrolled through and didn't find a confirmation about other browsers vendors, except Chrome. There is a link to a Mozilla/gecko repo where it's also raising an exception for external import maps.

I have a bad feeling about the future of this feature given it's taking already more than 3 years for Chrome and others to implement it, so I'd rather not run ahead of the locomotive.

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Not sure if we had a practice before in Modern Web with experimental feature plugins, maybe that can be a sort of in the middle solution. Curious if @thepassle @Westbrook @koddsson have an idea?

You can also make your own plugin meanwhile and publish it yourself.

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