test: add test for Astro components

[unindented]

Which issue does this PR address?

Repro for #22

[nikku]

Thanks for the PR! It allowed me to investigate this issue.

I checked what eslint-astro-parser generates as a syntax tree, parsing the source code file you provided:

---
const name = 'world';
---

<h1>Hello {name}!</h1>

The AST visible to this plug-in (and hence the one the plug-in derives it's magic and/or builds on top) is the following:

<ref *2> Node {
  type: 'Program',
  loc: { start: { line: 1, column: 0 }, end: { line: 6, column: 0 } },
  range: [ 0, 54, [length]: 2 ],
  body: [
    <ref *1> Node {
      type: 'VariableDeclaration',
      loc: { start: { line: 2, column: 0 }, end: { line: 2, column: 21 } },
      range: [ 4, 25, [length]: 2 ],
      declarations: [
        Node {
          type: 'VariableDeclarator',
          loc: [Object],
          range: [Array],
          id: [Node],
          init: [Node],
          [start]: [Getter],
          [end]: [Getter],
          parent: [Circular *1]
        },
        [length]: 1
      ],
      kind: 'const',
      [start]: [Getter],
      [end]: [Getter],
      parent: [Circular *2]
    },
    <ref *3> Node {
      type: 'AstroFragment',
      loc: { start: { line: 5, column: 0 }, end: { line: 6, column: 0 } },
      range: [ 31, 54, [length]: 2 ],
      children: [ ... ],
      [start]: [Getter],
      [end]: [Getter],
      parent: [Circular *2]
    },
    [length]: 2
  ]

You see that the first program node starts at character 4, behind the ---. The --- is available as Punctuation in the token list, but has no proper AST representation. Without any representation, and no way for the plug-in to find out about the context it operates in. So I'm afraid, we'll not be able to easily support .astro files.

You could ping back that question to the astro creators: How is consuming their parsers output supposed to work? Why do they hide the --- token? Svelte and Vue parsers don't hide essential information, hence allowing to detect their components.