Make templateExportDefault default to true

[bendemboski]

I don't think making removing export defaults the out-of-box behavior is the right way to go. In gjs files where there are no imports or other code, I think omitting the export default does make sense so it looks like "just HTML":

<template>
  Hello world
</template>

That's nice and clean! However, if there is other code in the file, especially other exports, I think it's confusing:

import { State } from '../utils/state.js';

export function createStateForComponent(data) {
  return new State(data, 'component1');
}

<template>
  {{@state.output}}
</template>

Now we have a mix of standard ES module syntax and...weird magic where there's no default export but somehow there is, and readers of the file just have to know that <template> tags are special-cased.

Moreover, it's pretty common (at least for me) to implement "private" components in gjs/gts files, e.g.

const Message = <template>
  <div>
    <span class="bold">{{@label}}:</span>
    {{@text}}
  </div>
</template>

<template>
  {{#each @messages as |msg|}}
    <Message @label={{msg.label}} @text={{msg.text}} />
  {{/each}}
</template>

So now readers have to know that <template> tags that are assigned to variables don't get exported, but the ones that aren't become the default export. Oh, and if you realize that you need a component class wrapping your template you have to add the export default. Oh, and if you have two "bare" <template> tags in a single file, it's an error even though it's not really evident why.

One of my favorite things about template tags is that template-only components become "regular values" like anything else that can be assigned to variables, passed to functions, etc etc. Once users adopt that mental model, I think it really starts unlocking the potential of low-overhead component composition, code organization, etc that template tags provide. So I really think that for consistency, clarity, and learning, our default happy-path should be that they follow ES module semantics as well and don't represent an exception.

If folks agree that this makes sense, I'm happy to open a PR.

[gitKrystan]

I see your point. We should probably bring this up in a forum with more eyes (Discord? RFC?) to get lots of opinions before deciding. Can you start a Discord thread on it?

[gitKrystan]

Thread: https://discord.com/channels/480462759797063690/1360340575357767723