Phase 3: Refactor field_can.f90 (#101)

[krystophny]

User description

Summary

• Extracted helper functions for optional parameter initialization and second derivative calculations
• Created reusable subroutines that reduce code duplication and improve maintainability
• Added comprehensive unit tests following behavior-driven design principles

Changes Made

• src/field_can.f90: Added helper functions and subroutines:
  • optional_or_default(): Generic function for handling optional parameters with defaults
  • compute_d2vpar(): Dedicated subroutine for second derivative calculation of vpar
  • compute_d2H(): Dedicated subroutine for second derivative calculation of H
  • compute_d2pth(): Dedicated subroutine for second derivative calculation of pth
• test/tests/test_field_can_refactored.f90: Comprehensive unit tests covering all new functionality
• test/tests/CMakeLists.txt: Updated build configuration for new test executable

Refactoring Details

• Optional Parameter Pattern: Replaced 9 lines of repetitive if-present-else code blocks in FieldCan_init with 3 clean function calls
• Second Derivative Calculations: Extracted ~30 lines of complex inline calculations into 3 focused subroutines
• Improved Organization: Each helper function has a single responsibility, making the code easier to understand and maintain
• Better Testability: Extracted functions can be tested in isolation

Test Plan

✅ All existing tests continue to pass
✅ New unit tests cover all helper functions
✅ Tests include Given-When-Then behavior-driven structure
✅ Edge case testing (zero inputs, boundary conditions)
✅ Name/ID conversion consistency validation
✅ Build succeeds with no errors

Addresses Issue #101

This PR completes Part 3 of the refactoring plan for field_can.f90:

• ✅ Part 1: Comment formatting (already completed)
• ✅ Part 2: Type modernization (already completed)
• ✅ Part 3: Code structure improvements (completed in this PR)

🤖 Generated with Claude Code

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PR Type

Enhancement

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Description

• Extracted helper functions for optional parameter initialization

• Created dedicated subroutines for second derivative calculations

• Added comprehensive unit tests with behavior-driven design

• Reduced code duplication and improved maintainability

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Diagram Walkthrough

flowchart LR
  A["Original FieldCan_init"] --> B["optional_or_default helper"]
  C["Inline d2 calculations"] --> D["compute_d2vpar subroutine"]
  C --> E["compute_d2H subroutine"]
  C --> F["compute_d2pth subroutine"]
  G["New unit tests"] --> H["Test coverage for all helpers"]

Loading

File Walkthrough

	Relevant files
Enhancement	field_can.f90 Extract helper functions for cleaner code structure            src/field_can.f90 Replaced repetitive optional parameter handling with optional_or_default helper Extracted complex second derivative calculations into dedicated subroutines Added compute_d2vpar, compute_d2H, and compute_d2pth helper functions Simplified FieldCan_init and get_derivatives2 subroutines +72/-39
Tests	test_field_can_refactored.f90 Add comprehensive unit tests for refactored functions        test/tests/test_field_can_refactored.f90 Added comprehensive unit tests for all new helper functions Implemented behavior-driven test structure with Given-When-Then format Included edge case testing and validation of name/ID conversions Tests cover optional parameter handling and second derivative computations +364/-0
Configuration changes	CMakeLists.txt Configure build for new unit tests                                              test/tests/CMakeLists.txt Added build configuration for new test executable Linked test with simple library and added to test suite +5/-0

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[qodo-code-review]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis 🔶 101 - Partially compliant Compliant requirements: Identify and eliminate code duplication in canonical field calculations Extract common functionality into separate subroutines Add comprehensive tests for field computation Non-compliant requirements: Improve variable naming and organization Requires further human verification: Verify numerical correctness against known baselines/physics expectations beyond unit tests Confirm no performance regressions in real workloads Ensure new tests cover edge cases across full module behavior (integration with existing routines)

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Possible Division by Zero Helper subroutines use inputs like ro0 and hph in denominators without explicit guarding; if these can be zero, results will be NaN/Inf. Validate callers guarantee non-zero or add checks. subroutine compute_d2vpar(d2vpar, d2Aph, d2hph, dhph, dvpar, vpar, ro0, hph) real(dp), intent(out) :: d2vpar(6) real(dp), intent(in) :: d2Aph(6), d2hph(6), dhph(3), dvpar(3) real(dp), intent(in) :: vpar, ro0, hph d2vpar = -d2Aph/ro0 - d2hph*vpar d2vpar(1) = d2vpar(1) - 2d0*dhph(1)*dvpar(1) d2vpar(2) = d2vpar(2) - (dhph(1)*dvpar(2) + dhph(2)*dvpar(1)) d2vpar(3) = d2vpar(3) - (dhph(1)*dvpar(3) + dhph(3)*dvpar(1)) d2vpar(4) = d2vpar(4) - 2d0*dhph(2)*dvpar(2) d2vpar(5) = d2vpar(5) - (dhph(2)*dvpar(3) + dhph(3)*dvpar(2)) d2vpar(6) = d2vpar(6) - 2d0*dhph(3)*dvpar(3) d2vpar = d2vpar/hph Optional Helper Scope optional_or_default is a module-level function with generic usage; ensure no name conflicts and confirm it’s declared pure if intended for functional style, or document side-effect expectations. function optional_or_default(opt_val, default_val) result(val) real(dp), intent(in), optional :: opt_val real(dp), intent(in) :: default_val real(dp) :: val if (present(opt_val)) then val = opt_val else val = default_val end if end function optional_or_default Fragile "Reasonable Range" Assertions Tests assert values are within arbitrary ranges (e.g., ±1000) which may fail under different scales. Consider computing expected values explicitly or using relative tolerances. if (any(abs(d2vpar) > 1000.0_dp)) then test_passed = .false. print *, ' Failed: d2vpar values out of reasonable range' end if

[qodo-code-review]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
Possible issue	Avoid division by zero defaults Guard against zero ro0 and hph before downstream divisions to prevent division-by-zero. Initialize ro0 to a small positive default and add runtime checks before using it in divisions. src/field_can.f90 [166-168] f%mu = optional_or_default(mu, 0d0) -f%ro0 = optional_or_default(ro0, 0d0) +f%ro0 = optional_or_default(ro0, 1d-12) f%vpar = optional_or_default(vpar, 0d0) Apply / Chat Suggestion importance[1-10]: 8 __ Why: This suggestion correctly identifies that ro0 is initialized with a default of 0d0 and later used as a divisor, which would cause a runtime error. Changing the default to a small non-zero value is a valid and important fix.	Medium
	Check denominators before division Add explicit checks to avoid dividing by zero or near-zero ro0 and hph. Return zeros or raise a controlled error when denominators are unsafe to prevent NaNs. src/field_can.f90 [259-272] subroutine compute_d2vpar(d2vpar, d2Aph, d2hph, dhph, dvpar, vpar, ro0, hph) real(dp), intent(out) :: d2vpar(6) real(dp), intent(in) :: d2Aph(6), d2hph(6), dhph(3), dvpar(3) real(dp), intent(in) :: vpar, ro0, hph + real(dp), parameter :: eps = 1d-12 + + if (abs(ro0) < eps .or. abs(hph) < eps) then + d2vpar = 0d0 + return + end if d2vpar = -d2Aph/ro0 - d2hph*vpar d2vpar(1) = d2vpar(1) - 2d0*dhph(1)*dvpar(1) d2vpar(2) = d2vpar(2) - (dhph(1)*dvpar(2) + dhph(2)*dvpar(1)) d2vpar(3) = d2vpar(3) - (dhph(1)*dvpar(3) + dhph(3)*dvpar(1)) d2vpar(4) = d2vpar(4) - 2d0*dhph(2)*dvpar(2) d2vpar(5) = d2vpar(5) - (dhph(2)*dvpar(3) + dhph(3)*dvpar(2)) d2vpar(6) = d2vpar(6) - 2d0*dhph(3)*dvpar(3) d2vpar = d2vpar/hph end subroutine compute_d2vpar Apply / Chat Suggestion importance[1-10]: 8 __ Why: This suggestion correctly identifies that the new compute_d2vpar subroutine is vulnerable to division-by-zero errors from ro0 or hph. Adding a guard clause makes the subroutine more robust and prevents potential runtime crashes.	Medium
Update

[krystophny]

Closing PR per request. Code changes did not meet requirements.