feat: Parser Enhancements Batch 8 - Array Subscript/Slice, Regex Operators & BETWEEN Tests

[ajitpratap0]

Summary

Implements three PostgreSQL parsing enhancements addressing Issues #180, #190, and #191.

Array Subscript & Slice Syntax (Issue #191)

• Add ArraySubscriptExpression AST node for element access: arr[1], matrix[2][3]
• Add ArraySliceExpression AST node for range slicing: arr[1:3], arr[2:], arr[:5]
• Support array access on parenthesized expressions: (expr)[1]
• Object pooling with Get/Put functions for memory efficiency
• 10 comprehensive parser tests

PostgreSQL Regex Operators (Issue #190)

• Add token mappings for ~, ~*, !~, !~* operators
• Support case-sensitive and case-insensitive regex matching
• 4 end-to-end tests including complex queries and subqueries

BETWEEN with Complex Expressions (Issue #180)

• Add comprehensive test coverage for existing functionality
• Tests for arithmetic, INTERVAL, subqueries, function calls
• Tests for CAST, CASE, string concatenation expressions
• 16 new tests across parser and high-level API

Files Changed

File	Changes
pkg/sql/ast/ast.go	+52 lines - New AST types
pkg/sql/ast/pool.go	+94 lines - Pool functions
pkg/sql/parser/expressions.go	+142 lines - Parser logic
pkg/sql/parser/token_converter.go	+6 lines - Regex tokens
Test files	+1651 lines - 30 new tests

Test plan

• All existing tests pass
• Race detection clean (go test -race ./...)
• Pre-commit hooks pass (fmt, vet, tests)
• CI pipeline passes

Closes

Closes #180, Closes #190, Closes #191

🤖 Generated with Claude Code

[claude]

Claude finished @ajitpratap0's task —— View job

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Code Review Complete

I've thoroughly analyzed PR #198 implementing array subscript/slice syntax, regex operators, and BETWEEN test enhancements. Here's my comprehensive review:

✅ Code Quality & Best Practices

Excellent Implementation Quality:

• Memory Management: Proper object pooling with GetArraySubscriptExpression() and GetArraySliceExpression() functions following the project's established patterns
• Error Handling: Comprehensive error messages with position information and helpful suggestions
• Code Organization: Clean separation between AST nodes, pooling logic, and parser implementation
• Documentation: Excellent inline documentation with usage examples and clear explanations
• Naming Conventions: Consistent with existing codebase (e.g., ArraySubscriptExpression, ArraySliceExpression)
• Test Coverage: Comprehensive test suite covering edge cases and complex scenarios

✅ Implementation Analysis

AST Changes (pkg/sql/ast/ast.go):

• New AST nodes properly implement the Expression interface
• ArraySubscriptExpression supports multi-dimensional arrays with Indices []Expression
• ArraySliceExpression supports PostgreSQL-style slicing with optional start/end bounds
• Token literals ("[]", "[:]") are appropriate and clear

Object Pooling (pkg/sql/ast/pool.go):

• Pool initialization with sensible initial capacities (Indices: make([]Expression, 0, 2))
• Proper cleanup in PutExpression() with iterative traversal (prevents stack overflow)
• Nil-safe operations and proper slice reset ([:0]) to preserve capacity
• Integrates seamlessly with existing pooling infrastructure

Parser Logic (pkg/sql/parser/expressions.go):

• Robust parseArrayAccessExpression() handles chaining: arr[1][2][3]
• Proper slice syntax parsing: arr[:], arr[1:], arr[:5], arr[1:3]
• Error handling for edge cases (empty brackets, malformed syntax)
• Correct precedence and associativity

Token Converter (pkg/sql/parser/token_converter.go):

• Clean mapping of regex operators: ~, ~*, !~, !~*
• Maintains both string and model token types for consistency
• No breaking changes to existing functionality

✅ Security Considerations

No Security Issues Found:

• Input validation is proper with bounds checking
• No SQL injection vulnerabilities introduced
• Error messages don't leak sensitive information
• Regex operators are parsed safely without evaluation

✅ Performance Considerations

Excellent Performance Design:

• Object Pooling: Reduces allocation pressure significantly
• Iterative Cleanup: PutExpression() uses work queue instead of recursion (prevents stack overflow)
• Efficient Parsing: Linear time complexity for array access chains
• Memory Efficiency: Pre-allocated slices with appropriate initial capacities
• Zero-Copy: Token conversion preserves references where possible

Performance Benchmarks Expected:

• Pool hit rates should remain >95% with new expression types
• No regression in parsing throughput expected
• Memory usage should decrease due to pooling

✅ Test Coverage Assessment

Comprehensive Test Coverage:

• Array Subscript Tests: Single/multi-dimensional, parenthesized expressions
• Array Slice Tests: All slice variants (:, 1:, :5, 1:3)
• Regex Operator Tests: All 4 operators in simple and complex queries
• BETWEEN Tests: Arithmetic, INTERVAL, subqueries, function calls, CAST expressions
• End-to-End Tests: Full tokenizer→parser pipeline validation
• Edge Cases: Error conditions, malformed syntax

🔍 Minor Observations

1. Array Index Types: The implementation accepts any Expression as array indices, which is flexible but might allow semantically invalid indices (e.g., arr[SELECT ...]). This is likely fine as semantic validation can be done separately.

2. Multi-dimensional Array Representation: Using nested ArraySubscriptExpression for matrix[2][3] is a clean approach that naturally represents the chaining.

3. Slice Semantics: The implementation follows PostgreSQL's slice semantics correctly with inclusive bounds.

✅ Alignment with Project Standards

Perfect Alignment:

• Follows CLAUDE.md guidelines for memory management
• Uses established error handling patterns with goerrors package
• Maintains thread-safety guarantees
• Proper defer patterns with pool returns
• Consistent with existing AST node patterns

✅ Recommendation

APPROVE - This is a high-quality implementation that:

• Adds significant functionality (PostgreSQL array syntax support)
• Maintains excellent code quality and performance characteristics
• Includes comprehensive test coverage
• Follows project conventions perfectly
• Introduces no security or performance regressions
• Addresses the specified issues (feat: Support BETWEEN with complex expressions #180, feat: Support PostgreSQL regular expression operators (~, ~*, !~, !~*) #190, feat: Support array subscript and slicing syntax #191) completely

Next Steps:

1. Ensure CI pipeline passes (particularly race detection tests)
2. Consider adding benchmark tests to validate performance claims
3. Update documentation to reflect new PostgreSQL array syntax support

This implementation demonstrates deep understanding of the codebase architecture and SQL parsing best practices. Excellent work!

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