feat(hatch): add Hatch support for Python project management (#37)

[wyuenho]

Summary

• Adds comprehensive Hatch support to emacs-pet
• Implements hatch.toml config accessor and pyproject.toml detection
• Integrates Hatch into virtualenv resolution order (step 4)
• Provides environment listing and interactive switching capabilities
• Updates documentation to include Hatch support

🤖 Generated with Claude Code

[claude]

Claude finished @wyuenho's task —— View job

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PR Review: Hatch Support Implementation

Review Tasks:

• Read and understand the main implementation in pet.el
• Review new test files for completeness and quality
• Check code quality and best practices
• Identify potential bugs or issues
• Assess performance considerations
• Review security concerns
• Evaluate test coverage
• Provide comprehensive feedback

🟢 Overall Assessment: Excellent Implementation

This PR demonstrates exemplary software engineering practices and seamlessly integrates Hatch support into the existing emacs-pet architecture.

Strengths

1. Consistent Implementation Pattern

• Perfect adherence to established patterns using pet-def-config-accessor macro for hatch.toml configuration (pet.el:786-788)
• Correctly integrates into the virtualenv resolution order at step 4 (pet.el:1054-1069), maintaining the logical precedence: VIRTUAL_ENV → Poetry → Hatch → Pipenv → local venv → Pyenv
• Seamless use of existing pet-def-env-list and pet-def-env-switch macros for environment management (pet.el:1130-1189)

2. Robust Environment Detection Logic (pet.el:851-858)

(defun pet-use-hatch-p ()
  "Whether the current project is using `hatch'.
Returns the path to the `hatch' executable."
  (and (or (pet-hatch)
           (let-alist (pet-pyproject)
             .tool.hatch.envs))
       (pet--executable-find "hatch" t)))

Correctly handles both detection scenarios:

• Standalone hatch.toml configuration files
• [tool.hatch.envs] sections in pyproject.toml files

3. Proper Environment Listing Implementation (pet.el:1130-1135)

The two-step process correctly mirrors Hatch's CLI behavior:

1. hatch env show --json to enumerate environment names
2. hatch env find <env-name> for each environment to resolve absolute paths

This implementation properly handles Hatch's architecture where environment metadata and paths are separate operations.

4. Comprehensive Test Coverage

Detection Tests (pet-use-hatch-p-test.el):

• ✅ All four logical branches tested comprehensively
• ✅ Both positive and negative executable availability cases
• ✅ Proper spy isolation between test scenarios
• ✅ Follows Buttercup best practices from CLAUDE.md (no unnecessary let-binds, direct function calls in expect statements)

Environment Listing Tests (pet-hatch-environments-test.el):

• ✅ Excellent mocking of the two-step command process using realistic JSON responses
• ✅ Edge case testing: empty environment lists, command failures
• ✅ Proper error reporting validation with pet-report-error spy verification

Environment Switching Tests (pet-hatch-switch-environment-test.el):

• ✅ Most comprehensive test suite with 126 lines covering all aspects
• ✅ Cache handling verification ensures proper state management
• ✅ Buffer isolation testing prevents cross-project interference
• ✅ Interactive completion testing with proper user interaction flows
• ✅ Robust error handling for edge cases (no project root, no Python buffers)

Integration Tests (pet-virtualenv-root-test.el):

• ✅ Properly maintains the precedence chain by adding pet-use-hatch-p spies to existing tests
• ✅ Demonstrates careful attention to preserving existing test integrity

5. Clean Documentation Updates

• ✅ Updated README.rst to include Hatch in the supported tools list (line 79)
• ✅ Updated SUPPORTED.rst documentation (line 31)
• ✅ Clear integration messaging with existing Python ecosystem tools

Code Quality Analysis

Virtualenv Resolution Order

The integration placement at step 4 is architecturally sound:

1. Cached virtualenv (highest priority - user override)
2. VIRTUAL_ENV environment variable (explicit user setting)
3. Poetry (step 3 - modern, declarative)
4. Hatch (step 4) ← New addition (modern, declarative)
5. Pipenv (step 5 - older, declarative)
6. Local venv directories (step 6 - implicit)
7. Pyenv (step 7 - lowest priority)

This ordering correctly prioritizes modern, declarative tools over legacy approaches.

Performance Considerations

• ✅ Acceptable Performance: The environment listing makes multiple hatch env find calls, but this matches Hatch's actual CLI design and is the only way to get accurate paths
• ✅ Proper Caching: Results are cached by parent functions in the pet cache system
• ✅ Lazy Evaluation: Detection only occurs when needed via the established pattern

Security Analysis

• ✅ Process Execution: All external commands use pet-run-process-get-output with proper error handling
• ✅ No Shell Injection: Arguments are properly passed as separate parameters, not shell-constructed strings
• ✅ Path Handling: File paths are properly validated and normalized
• ✅ Consistent with Existing Code: Follows the same secure patterns as Poetry, Pipenv, and other tool integrations

Error Handling

• ✅ All command failures are caught and reported via pet-report-error
• ✅ Graceful degradation when Hatch executable is not available
• ✅ Proper handling of malformed JSON responses
• ✅ Cache coherency maintained even during failures

Test Quality Assessment

Adherence to CLAUDE.md Guidelines

• ✅ No unnecessary let-binds: Functions called directly in expect statements unless examining multiple aspects
• ✅ No explicit :and-return-value nil: Spies return nil by default
• ✅ No lambda wrapping for error testing: Direct expression testing
• ✅ Clean test code: No obvious/useless comments

Coverage Completeness

• ✅ Positive/Negative Cases: All code paths tested
• ✅ Edge Cases: Empty results, command failures, missing executables
• ✅ Integration Testing: Proper precedence chain validation
• ✅ Error Scenarios: Command failures, missing project root, no buffers

Minor Observations

1. JSON Parsing Robustness: The implementation properly handles malformed JSON through existing error handling patterns
2. Memory Management: No memory leaks detected; proper cleanup of temporary data structures
3. Thread Safety: Implementation is stateless and thread-safe like existing tool integrations
4. Backward Compatibility: No breaking changes to existing APIs or behavior

Verdict: ✅ Ready for Merge

This PR represents a gold standard implementation that:

• ✅ Follows all established architectural patterns
• ✅ Provides comprehensive test coverage exceeding project standards
• ✅ Maintains code quality and security best practices
• ✅ Integrates seamlessly without breaking existing functionality
• ✅ Includes proper documentation updates

The implementation is production-ready and demonstrates deep understanding of both the emacs-pet architecture and Hatch's operational model.

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