feat: port rule no-var

[fansenze]

Summary

Port the no-var rule from ESLint to rslint.

Require let or const instead of var

Related Links

• Tracking issue: [Tracking]: eslint core rules #223

• ESLint rule: https://eslint.org/docs/latest/rules/no-var

• Source code: https://github.com/eslint/eslint/blob/main/lib/rules/no-var.js

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the no-var rule, a significant addition to the linter's capabilities. Its primary goal is to guide developers towards modern JavaScript variable declaration practices by flagging instances of var and promoting the use of let and const. This change enhances code quality and consistency across projects using rslint by aligning with current best practices.

Highlights

• New Linting Rule: Implemented the no-var rule, which disallows the use of var for variable declarations, promoting let and const instead.
• Rule Integration: The new no-var rule has been integrated into the rslint configuration and registered for use.
• Comprehensive Testing and Documentation: Added dedicated Go-based unit tests, TypeScript-based RuleTester tests, snapshot tests, and markdown documentation for the no-var rule.

Changelog

• internal/config/config.go
  • Imported the no_var rule package.
  • Registered the no-var rule in the global rule registry.
• internal/rules/no_var/no_var.go
  • Added the NoVarRule definition, including its name and Run function.
  • Implemented the rule logic to identify VariableStatement nodes that are not block-scoped (i.e., var declarations) and report them.
• internal/rules/no_var/no_var.md
  • Created documentation explaining the no-var rule, its purpose, and providing examples of correct and incorrect code.
• internal/rules/no_var/no_var_test.go
  • Added Go-based unit tests for the no-var rule, including valid and invalid test cases ported from ESLint.
• packages/rslint-test-tools/rstest.config.mts
  • Updated the test configuration to include the new no-var.test.ts file.
• packages/rslint-test-tools/tests/eslint/rules/snapshots/no-var.test.ts.snap
  • Generated snapshot tests for the no-var rule's invalid cases, capturing diagnostic output.
• packages/rslint-test-tools/tests/eslint/rules/no-var.test.ts
  • Added TypeScript-based RuleTester tests for the no-var rule, defining valid and invalid code examples.

Activity

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[gemini-code-assist]

Code Review

This pull request ports the no-var rule from ESLint. The implementation is a good start, but it currently misses detecting var declarations inside loop initializers (for, for-in, for-of), which is a key part of this rule's functionality. I've provided a suggestion to fix the rule implementation to cover these cases. I've also suggested adding corresponding test cases to both the Go unit tests and the TypeScript E2E tests to ensure complete coverage and prevent regressions.