feat: implement css codemods for vue sfc files using postcss

[Sidnioulz]

Closes #16

• Add PostCSS-based CSS transformation API inspired by JSCodeshift
• Support CSS, SCSS, and Less syntax parsing
• Implement comprehensive transformation context with PostCSS AST access
• Add support for Vue-specific features (scoped styles, deep selectors, CSS modules)
• Create extensive test suite covering all major CSS transformation scenarios
• Add three example transformations:
  • CSS class prefix addition with configurable prefix
  • Vue deep selector syntax conversion (:deep() to ::v-deep)
  • CSS color values to CSS custom properties conversion
• Maintain backward compatibility with existing codebase

🤖 Generated with Claude Code

[codecov]

Codecov Report

Attention: Patch coverage is 93.50649% with 5 lines in your changes missing coverage. Please review.

Project coverage is 82.66%. Comparing base (de81ac4) to head (b686cad).

Files with missing lines	Patch %	Lines
src/transformStyle.ts	93.50%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #156      +/-   ##
==========================================
+ Coverage   81.23%   82.66%   +1.43%     
==========================================
  Files          22       22              
  Lines        1993     2060      +67     
  Branches      215      232      +17     
==========================================
+ Hits         1619     1703      +84     
+ Misses        369      351      -18     
- Partials        5        6       +1     

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[Copilot]

Pull Request Overview

This PR introduces a PostCSS-based CSS transformation API for Vue SFCs, adds parser support for CSS/SCSS/Less, and provides examples and tests for common codemods.

• Define new types (StyleTransformationFileInfo, StyleTransformationContext) and update StyleTransformation signature
• Implement transformStyle runner with PostCSS parsing, context creation, and result handling
• Add comprehensive tests and real-world examples (class prefixing, Vue deep selector conversion, color variable conversion)

Reviewed Changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/types/StyleTransformation.ts	Added types for style transformation API
src/transformStyle.ts	Implemented the core CSS transformation runner
src/tests/transformStyle.spec.ts	Added tests covering CSS, SCSS, Less, return types, and errors
package.json	Registered PostCSS and related dependencies
examples/css-vue-deep-transform/transformation.cjs	Example for Vue deep/slotted selector conversion
examples/css-vue-deep-transform/Input.vue	Vue SFC demonstrating deep/slotted syntax
examples/css-prefix-classes/transformation.cjs	Example for CSS class prefix addition
examples/css-prefix-classes/Input.vue	Vue SFC demonstrating class prefix example
examples/css-color-variables/transformation.cjs	Example for converting color literals to CSS custom properties
examples/css-color-variables/Input.vue	Vue SFC with color variable declarations (has formatting issue)

Comments suppressed due to low confidence (3)

src/transformStyle.ts:28

• [nitpick] Rename the params parameter to options to match the StyleTransformation signature and improve consistency.

  params: Options,

examples/css-color-variables/Input.vue:9

• The CSS rules are appended directly to the <style> tag instead of inside the block. Split this into <style scoped> on its own line, followed by the :root { ... } block.

<style scoped>:root {

package.json:71

• These dependencies (postcss-selector-parser, postcss-value-parser) are not used in the codebase. Consider removing them to keep the dependency list lean.

    "postcss-selector-parser": "^7.1.0",

[Copilot]

[nitpick] Avoid calling prefix.replace('-', '') inside the loop on every rule. Compute the cleaned prefix once outside of root.walkRules for better clarity and slight performance gain.

Suggested change

	// Transform class selectors
	root.walkRules((rule) => {
	rule.selector = rule.selector.replace(/\.([a-zA-Z][\w-]*)/g, (match, className) => {
	// Don't prefix if it already has the prefix
	if (className.startsWith(prefix.replace('-', ''))) {
	const cleanedPrefix = prefix.replace('-', '')
	// Transform class selectors
	root.walkRules((rule) => {
	rule.selector = rule.selector.replace(/\.([a-zA-Z][\w-]*)/g, (match, className) => {
	// Don't prefix if it already has the prefix
	if (className.startsWith(cleanedPrefix)) {