Modernize CEL API usage: Remove deprecated ref.TypeProvider and ref.FieldType

[richardwooding]

Summary

The current implementation uses deprecated CEL API types:

• ref.TypeProvider (deprecated in favor of types.Provider)
• ref.FieldType (deprecated in favor of types.FieldType)

Changes Needed

Provider Interface

• Update TypeProvider interface to embed types.Provider instead of ref.TypeProvider
• Implement modern types.Provider methods:
  • FindStructType(string) (*types.Type, bool)
  • FindStructFieldNames(string) ([]string, bool)
  • FindStructFieldType(string, string) (*types.FieldType, bool)
  • NewValue(string, map[string]ref.Val) ref.Val

Tests

• Update pg/provider_test.go to use modern API
  • Replace FindType() calls with FindStructType()
  • Replace FindFieldType() calls with FindStructFieldType()
  • Update test expectations from *exprpb.Type to *types.Type
  • Update test expectations from *ref.FieldType to *types.FieldType
• Update pg/provider_testcontainer_test.go to use modern API

Backward Compatibility

• Consider adding a compatibility layer if external users depend on the old interface
• Document migration path for users upgrading to the new API

Benefits

• Future-proof against CEL API changes
• Remove deprecation warnings from linter
• Align with modern CEL best practices
• Cleaner type system integration

Implementation Status

• Interface updated to use types.Provider
• Modern methods implemented
• Tests updated (in progress)
• Backward compatibility considered

This modernization ensures cel2sql remains compatible with current and future CEL versions while providing a cleaner, more maintainable API.

[richardwooding]

✅ Modernization Complete

All deprecated CEL API usage has been successfully removed from the codebase. Here's what was completed:

Core Changes

• Provider Interface: Updated TypeProvider interface to embed types.Provider instead of ref.TypeProvider
• Method Migration: Replaced deprecated methods with modern equivalents:
  • FindType() → FindStructType()
  • FindFieldType() → FindStructFieldType()
  • FindStructFieldNames() added for field enumeration
• Type System: Updated type handling to use types.Type and types.FieldType instead of ref.FieldType

Test Updates

• Unit Tests: Updated all tests in pg/provider_test.go to use modern API
• Integration Tests: Updated testcontainer tests to use modern API
• Test Data: Fixed test expectations to match actual schema definitions

Documentation

• Code Comments: Updated all API documentation
• Contributing Guide: Updated example code to use modern API
• Migration Path: All deprecated usage removed, no backward compatibility needed

Quality Assurance

• ✅ All tests passing (60+ test cases)
• ✅ Linting clean (golangci-lint)
• ✅ No remaining deprecated API usage
• ✅ PostgreSQL integration tests working

The project now uses the latest CEL-Go v0.25.0 API exclusively with no deprecated dependencies. All functionality has been preserved while modernizing the codebase.