Vue Component Style Extractor Webpack Loader

This challenge asks you to create a webpack loader that extracts CSS styles from Vue components and outputs them as a separate CSS file. This is useful for optimizing CSS delivery, enabling code splitting of styles, and improving caching efficiency. The loader will parse Vue component files, identify <style> blocks, and extract the CSS content.

Problem Description

You need to build a webpack loader that processes Vue component files (.vue) and extracts the CSS content from <style> tags within those files. The loader should:

1. Identify Vue Component Files: The loader should only target files with the .vue extension.
2. Parse the File: Use a suitable library (e.g., vue-template-compiler) to parse the Vue component file and extract its content.
3. Extract CSS: Locate all <style> tags within the parsed component. Extract the CSS content from each <style> tag. Handle different scoped attributes correctly (see notes).
4. Return CSS as String: The loader should return a single string containing all the extracted CSS, concatenated together.
5. Handle scoped attribute: If a <style> tag has the scoped attribute, the CSS should be processed as if it were not scoped. This means the loader should not add the scoped attribute to the output CSS. It should simply extract the CSS content.
6. Handle multiple <style> tags: The loader should correctly extract and concatenate CSS from multiple <style> tags within a single component.

Expected Behavior:

When the loader encounters a .vue file, it should parse the file, extract all CSS from <style> tags (regardless of scoped attribute), concatenate them into a single string, and return that string. Webpack will then treat this string as the output of the loader and can be further processed (e.g., minified, bundled).

Edge Cases to Consider:

• No <style> tags: The loader should return an empty string if the component doesn't contain any <style> tags.
• Invalid Vue syntax: The loader should handle cases where the Vue component file has invalid syntax gracefully (e.g., by returning an empty string or throwing a controlled error). For this challenge, returning an empty string is acceptable.
• CSS with comments: The loader should preserve CSS comments within the extracted CSS.
• Different CSS dialects: The loader should handle different CSS dialects (e.g., CSS, SCSS, LESS) as long as they are valid CSS within the <style> tags. The loader itself doesn't need to process these dialects; it just needs to extract them.

Examples

Example 1:

Input:
```vue
<template>
  <div>Hello</div>
</template>

<style scoped>
h1 {
  color: blue;
}
</style>

Output:

h1 {
  color: blue;
}

Explanation: The loader extracts the CSS from the <style scoped> block and returns it as a string, removing the scoped attribute.

Example 2:

Input:
```vue
<template>
  <div>Hello</div>
</template>

<style>
h1 {
  color: red;
}

p {
  font-size: 16px;
}
</style>

Output:

h1 {
  color: red;
}

p {
  font-size: 16px;
}

Explanation: The loader extracts CSS from both <style> blocks and concatenates them into a single string.

Example 3:

Input:
```vue
<template>
  <div>Hello</div>
</template>

Output:

Explanation: The component has no <style> tags, so the loader returns an empty string.

Constraints

• File Size: The loader should be able to handle Vue component files up to 1MB in size.
• Performance: The loader should process files reasonably quickly (within a few hundred milliseconds for typical components). While optimization is encouraged, it's not the primary focus of this challenge.
• Dependencies: You are allowed to use external libraries like vue-template-compiler. Minimize dependencies where possible.
• Typescript: The loader must be written in Typescript.

Notes

• The scoped attribute in Vue components is a mechanism for CSS modules. This loader is not intended to implement CSS modules itself. It simply needs to extract the CSS content regardless of the scoped attribute.
• Consider using vue-template-compiler to parse the Vue component files. This library provides a reliable way to extract the component's content.
• The loader should be designed to be compatible with standard webpack configurations.
• The loader should not modify the original Vue component file. It should only extract the CSS content.
• Error handling is important, but for simplicity, you can choose to return an empty string in case of errors during parsing. Focus on the core extraction logic.
• The output CSS should be a single string, with CSS rules separated by newlines.