feat(rules): implement pattern string lexer for tokenization

[fohte]

Why

• The pattern parser requires a lexer as its first stage to split pattern strings (e.g. "curl -X|--request POST *") into raw tokens
  • The parser cannot recognize syntactic elements (alternation, wildcards, negation) in rule patterns without a lexer

What

• Add a pattern string lexer (pattern_lexer) to the rules module
  • Recognize alternation (-X|--request), wildcards (*), negation (!value), optional groups ([...]), placeholders (<cmd>, <path:name>), and quoted strings
  • Return errors for malformed syntax (unclosed brackets, nested square brackets, empty alternation parts)

---

[gemini-code-assist]

Summary of Changes

Hello @fohte, 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 foundational pattern_lexer module, a critical first step for the upcoming pattern parser in the rules component. The lexer is responsible for breaking down complex pattern strings into a stream of recognizable tokens, enabling the parser to understand syntactic elements such as alternations, wildcards, negations, and optional groups. This ensures that rule patterns can be accurately interpreted and processed.

Highlights

• New pattern_lexer module: Introduced a new pattern_lexer module to the rules component, which is the first stage for parsing pattern strings.
• LexToken Enum Definition: Defined the LexToken enum to represent various syntactic elements like literals, alternations, wildcards, negations, optional groups, and placeholders.
• Tokenization Logic: Implemented the core tokenize function, which processes pattern strings and converts them into a sequence of LexTokens, handling different pattern constructs.
• Robust Error Handling: Incorporated robust error handling for malformed patterns, including unclosed quotes, unclosed angle brackets, unclosed square brackets, nested square brackets, and empty alternation parts.
• Comprehensive Unit Tests: Added comprehensive unit tests to validate the lexer's behavior across various valid and erroneous pattern string scenarios, ensuring correctness and reliability.

Changelog

• src/rules/mod.rs
  • Exported the new pattern_lexer module to make it publicly accessible within the rules component.
• src/rules/pattern_lexer.rs
  • Added LexToken enum for representing different token types found in pattern strings.
  • Implemented the tokenize function for converting raw pattern strings into a structured sequence of LexTokens.
  • Included helper functions such as consume_word, is_word_boundary, classify_word, classify_negation, and validate_alternation_parts to support the tokenization process.
  • Integrated comprehensive unit tests covering basic literals, alternations, wildcards, negations, square brackets, placeholders, quoted strings, complex patterns, whitespace handling, and various error conditions.

Activity

• fohte created this pull request to implement the pattern string lexer, laying the groundwork for future pattern parsing capabilities.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.

[gemini-code-assist]

Code Review

This pull request introduces a new lexer for rule patterns, which is a crucial first step for the pattern parser. The implementation is well-structured and comes with a comprehensive test suite covering various cases, including literals, alternations, wildcards, negations, and more.

I've added a couple of suggestions to improve the code further by reducing duplication and using more idiomatic Rust constructs. Overall, this is a solid contribution.