feat: improve prefilter

[shu-kitamura]

This pull request introduces a comprehensive regex pattern analysis to the regex-core crate, enabling extraction of deterministic "must-have" substrings, candidate literals (needles), and nullability from regex ASTs. The engine and evaluator APIs are updated to leverage these analyses, improving pre-filtering and match logic. Extensive tests are added to verify correctness and edge cases.

Regex pattern analysis and integration:

• Added the AstAnalysis struct and the analyze_ast function to engine/ast.rs, which extract must-have substrings, candidate literals, and nullability from regex ASTs. Limits are enforced to prefer longer literals and lexicographic order.
• Updated the Regex struct in lib.rs to store must_literals, needles, and nullable, and to initialize these via compile_pattern_with_analysis, replacing the previous first_strings logic. [1] [2]
• Added new engine functions: compile_pattern_with_analysis and compile_pattern_with_must_literals, which return compiled instructions along with analysis results.

Evaluator and matching improvements:

• Changed eval_from_start to eval_from_starts in evaluator.rs, allowing matching from multiple provided start indices, and updated engine and tests accordingly. [1] [2]
• Updated tests in engine.rs and evaluator.rs to verify new analysis features, must literals extraction, needle extraction, nullability, and multi-start matching. [1] [2] [3]

Documentation and review instructions:

• Added a Japanese-language code review checklist for Copilot reviewers in .github/instructions/review/pr-review.instructions.md, emphasizing code quality, naming, error handling, test coverage, and performance.

[Copilot]

Pull request overview

This pull request introduces comprehensive regex pattern analysis to improve prefiltering performance in the regex-core crate. The changes extract deterministic "must-have" literals, candidate literals (needles), and nullability from regex ASTs, enabling more efficient matching through multi-level prefiltering before full VM evaluation.

Changes:

• Added AST analysis infrastructure (AstAnalysis struct and analyze_ast function) to extract must_literals, needles, and nullability from regex patterns
• Updated the Regex API to leverage analysis results with a multi-level prefiltering strategy (nullable check → must_literals check → needle-based position hints → full VM scan)
• Modified evaluator to support matching from multiple candidate start positions via eval_from_starts

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/regex-core/src/engine/ast.rs	Implements AST analysis with functions to extract must_literals, needles, and nullable flags; includes comprehensive tests
crates/regex-core/src/lib.rs	Integrates analysis results into Regex struct; implements multi-level prefiltering strategy in is_match_line
crates/regex-core/src/engine.rs	Adds compile_pattern_with_analysis and compile_pattern_with_must_literals functions; updates match_line_from_start to match_line_from_starts
crates/regex-core/src/engine/evaluator.rs	Changes eval_from_start to eval_from_starts to support multiple start positions
.github/instructions/review/pr-review.instructions.md	Adds code review checklist guidelines for Copilot reviewers (requests Japanese responses)