Wrap structs by kwabenantim · Pull Request #117 · Chaste/cppwg

kwabenantim · 2026-08-10T10:19:47Z

Fixes #116

A struct that was not the single-nested-enum special case was silently dropped by the class writer (no wrapper file), yet the module writer still emitted its #include and register_..._class call, producing an opaque missing-header compile error (or the unlinkable-struct mismatch). Route any non-single-enum struct through the normal py::class_ path (its members are public by default), and bind public data members with def_readwrite (or def_readonly for const members) via a new CppClassMemberWrapperWriter. Static and bitfield members, which have no usable address, are skipped; the existing excluded_variables option (previously unused) suppresses a named field. The change applies to all wrapped classes, not just structs. package_info._wrapped_types now also walks public data members (same skips) so a member type drives dependency pruning and auto-includes, keeping it in lockstep with the writers. When a class produces no wrapper code at all, warn instead of silently writing nothing. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add a plain data struct ShapeMetrics to the primitives module: mutable members bound with def_readwrite, a const member with def_readonly, and a field suppressed via excluded_variables. Regenerate the wrappers and add a test that constructs the struct, round-trips a field, checks the const field is read-only, and confirms the excluded field is absent. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Note that a plain struct is wrapped as a normal class, that public data members are exposed with def_readwrite/def_readonly, and that excluded_variables suppresses a field. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Several example headers used run-together include guards (ABSTRACTPOLYGON_HPP_) while others already separated words with underscores (SIMPLE_MATH_FUNCTIONS_HPP_). Standardise both example projects on the word-separated form. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add unit tests for the paths the initial #116 tests missed: a class that produces no register blocks (warns, writes nothing), a plain non-struct class taking the normal member-binding path, and an abstract class with an abstract base whose constructors are not wrapped but whose public data members still drive dependency/auto-include resolution. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

codecov · 2026-08-10T10:20:25Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.69%. Comparing base (5ebccf8) to head (55f9629).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #117      +/-   ##
===========================================
+ Coverage    99.68%   99.69%   +0.01%     
===========================================
  Files           27       28       +1     
  Lines         2203     2282      +79     
  Branches       487      507      +20     
===========================================
+ Hits          2196     2275      +79     
  Misses           6        6              
  Partials         1        1

Flag	Coverage Δ
cells	`75.59% <21.25%> (-1.94%)`	⬇️
shapes	`76.16% <68.75%> (-0.15%)`	⬇️
unit	`92.41% <100.00%> (+1.18%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cppwg/info/package_info.py	`99.23% <100.00%> (+0.04%)`	⬆️
cppwg/templates/pybind11_default.py	`100.00% <100.00%> (ø)`
cppwg/utils/utils.py	`100.00% <100.00%> (ø)`
cppwg/writers/class_writer.py	`98.77% <100.00%> (+0.01%)`	⬆️
cppwg/writers/member_variable_writer.py	`100.00% <100.00%> (ø)`

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Pull request overview

Fixes #116 by wrapping ordinary structs through the class path and exposing public data members.

Changes:

Adds read/write and const read-only member bindings with exclusions.
Includes member types in dependency discovery.
Adds unit, integration, generated-wrapper, and documentation coverage.

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`cppwg/writers/member_variable_writer.py`	Generates public member bindings.
`cppwg/writers/class_writer.py`	Routes ordinary structs through class generation.
`cppwg/templates/pybind11_default.py`	Adds the member-binding template.
`cppwg/info/package_info.py`	Includes member types in dependency analysis.
`tests/test_member_variable_writer.py`	Tests member-binding behavior.
`tests/test_class_writer.py`	Tests struct wrapping and exclusions.
`tests/test_package_info.py`	Tests member dependency discovery.
`doc/reference.md`	Documents struct and variable support.
`doc/basics.md`	Documents variable exclusions.
`examples/shapes/src/cpp/primitives/ShapeMetrics.hpp`	Adds an example data struct.
`examples/shapes/wrapper/package_info.yaml`	Configures the example struct.
`examples/shapes/src/py/tests/test_classes.py`	Tests generated Python behavior.
`examples/shapes/wrapper/primitives/ShapeMetrics.cppwg.hpp`	Adds generated registration declaration.
`examples/shapes/wrapper/primitives/ShapeMetrics.cppwg.cpp`	Adds generated member bindings.
`examples/shapes/wrapper/primitives/_pyshapes_primitives.main.cppwg.cpp`	Registers the example struct.
`examples/shapes/wrapper/wrapper_header_collection.cppwg.hpp`	Includes the example header.
`examples/shapes/src/cpp/primitives/UnitSquare.hpp`	Normalizes the include guard.
`examples/shapes/src/cpp/primitives/ShapeKind.hpp`	Normalizes the include guard.
`examples/shapes/src/cpp/primitives/RegularPolygon.hpp`	Normalizes the include guard.
`examples/shapes/src/cpp/primitives/AreaUnits.hpp`	Normalizes the include guard.
`examples/shapes/src/cpp/primitives/AbstractShape.hpp`	Normalizes the include guard.
`examples/shapes/src/cpp/primitives/AbstractPolygon.hpp`	Normalizes the include guard.
`examples/cells/src/cpp/utils/SimulationException.hpp`	Normalizes the include guard.
`examples/cells/src/cpp/utils/PetscUtils.hpp`	Normalizes the include guard.
`examples/cells/src/cpp/mesh/MacroMesh.hpp`	Normalizes the include guard.
`examples/cells/src/cpp/cell/CellFactory.hpp`	Normalizes the include guard.

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A public C-style array member (e.g. `double coords[3]`) would emit `.def_readwrite("field", &Cls::field)`, but pybind11's generated setter assigns to the member and C arrays are not assignable, so the wrapper fails to compile (def_readonly is no better: pybind11 has no caster for a raw array). Skip array members with a debug log, alongside the existing bitfield/static skips, and mirror the skip in the package_info member walk so an array member's type no longer drives a spurious dependency or auto-include. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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Pull request overview

Copilot reviewed 26 out of 26 changed files in this pull request and generated 2 comments.

Suppressed comments (3)

cppwg/info/package_info.py:629

Keep dependency discovery restricted to direct data members too. pygccxml recurses into nested declarations by default, so nested fields can currently add spurious auto-includes or even prune the outer wrapper for a dependency that is never actually bound.

        for variable in decl.variables(function=query, allow_empty=True):

doc/reference.md:110

The implementation also skips C-style array members, but this new public-facing note lists only static and bitfield members. Document arrays here so users understand why a public array field is absent from Python.

[`excluded_variables`](#common-options) to suppress a field. Static and bitfield
members are skipped. (The only special case is a struct wrapping a single nested

cppwg/info/package_info.py:628

This walk now yields data-member types for the single-enum struct special case, but CppClassWrapperWriter.write() routes that declaration to build_struct_enum_register() and never binds its members. Consequently, an uninstantiated member type can incorrectly prune an otherwise valid enum wrapper, and auto-includes can be added for code that is not emitted. Detect the struct-enum dispatch before walking methods, constructors, or members so this helper continues to represent only generated bindings.

This issue also appears on line 629 of the same file.

        # Public data members are bound with def_readwrite/def_readonly, so their
        # types are wrapped too. Mirror the member writer's skips (excluded_variables,
        # static, bitfield, array) so a member type reached only through a skipped
        # member does not trigger a dependency or auto-include.
        excluded_variables = gather("excluded_variables")

Two more member kinds cannot be bound with def_readwrite/def_readonly: - A reference member (`T& field`) has no pointer-to-member, so &Class::field is ill-formed. - The variables() query is recursive, so it also returns fields of nested classes (e.g. an iterator); binding one as &Class::field names a member the outer class does not have. The method/constructor writers already guard this with a parent check; the member writer now does too. Skip both in the member writer and mirror them in the package_info dependency walk. Also short-circuit that walk for the single-nested-enum struct special case: such a struct is registered as a py::enum_ and binds none of its methods/constructors/members, so it introduces no wrapped types. Update the reference.md note to list the full skip set. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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Pull request overview

Copilot reviewed 26 out of 26 changed files in this pull request and generated no new comments.

Suppressed comments (1)

cppwg/writers/member_variable_writer.py:146

Mutable does not imply copy-assignable. pybind11's def_readwrite setter performs c.*pm = value, so fields such as std::unique_ptr<T> or std::atomic<T> instantiate a deleted copy assignment operator and make the generated wrapper fail to compile. Please detect non-copy-assignable member types and either expose them read-only or skip them, and mirror that decision in the dependency walk.

        # A const member cannot be written from Python, so bind it read-only.
        if declarations.is_const(self.variable_decl.decl_type):
            access = "readonly"
        else:
            access = "readwrite"

pybind11's def_readwrite setter performs obj.*pm = value, so a mutable member whose type is not copy-assignable makes the generated wrapper fail to compile. This bites move-only types (std::unique_ptr), std::atomic (deleted copy assignment) and any class with a user-deleted operator=. Add utils.type_is_copy_assignable(decl_type): fundamentals, pointers and enums are always assignable; a class type is treated as non-assignable if pygccxml reports it noncopyable (catches unique_ptr/atomic, which still expose a public move/value operator= that a public-assign check alone would miss) or as lacking a public assignment operator (catches a plainly deleted copy assignment). The member writer skips such members when they would be bound read-write; const members are read-only (no setter) and are unaffected. Mirror the skip in the package_info dependency walk, and note it in reference.md. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

kwabenantim and others added 5 commits August 5, 2026 11:16

#116 Document struct wrapping and public data members

fe33927

Note that a plain struct is wrapped as a normal class, that public data members are exposed with def_readwrite/def_readonly, and that excluded_variables suppresses a field. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

kwabenantim requested a balanced review from Copilot August 10, 2026 10:20

kwabenantim marked this pull request as ready for review August 10, 2026 10:20

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kwabenantim mentioned this pull request Aug 10, 2026

Improve python wrapper config Chaste/Chaste#576

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kwabenantim requested a balanced review from Copilot August 10, 2026 11:48

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kwabenantim merged commit 4f3929d into develop Aug 10, 2026
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kwabenantim deleted the 116-wrap-structs branch August 10, 2026 12:55

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Wrap structs - #117

Wrap structs#117
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