feat: light zero copy derive add unit struct support #2144

ananas-block · 2025-12-19T00:31:09Z

Summary by CodeRabbit

New Features
- Added support for unit structs (empty structs) to the zero-copy derive macro, enabling zero-copy operations on unit struct types.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

coderabbitai · 2025-12-19T00:31:19Z

Walkthrough

Extended the zero-copy-derive macro to support unit structs (e.g., struct Foo;) by introducing an InputType::UnitStruct variant and updating code generation paths in four files to handle zero-field structs via type aliases and specialized trait implementations.

Changes

Cohort / File(s)	Summary
Input type classification `program-libs/zero-copy-derive/src/shared/utils.rs`	Added `UnitStruct` variant to public `InputType<'a>` enum; updated `process_input()` and `process_input_generic()` signatures to return `Option<&FieldsNamed>` and `InputType<'_>` respectively, enabling detection and classification of unit structs vs. named-field structs
Zero-copy reference implementation `program-libs/zero-copy-derive/src/zero_copy.rs`	Added code path for unit structs generating: public type alias `pub type <ZName<'a>> = &'a <Name>;`, and trait impl `ZeroCopyAt<'a>` that returns a reference to a static unit instance
Equality trait derivation `program-libs/zero-copy-derive/src/zero_copy_eq.rs`	Added early-return branch for unit structs (zero fields) that generates `PartialEq` impls always returning `true`, bypassing standard field-processing logic
Mutable reference implementation `program-libs/zero-copy-derive/src/zero_copy_mut.rs`	Added code path for unit structs generating: mutable type alias `{ZStructName}Mut<'a>`, config type alias `{Name}Config = ()`, and trait impls `ZeroCopyAtMut<'a>` and `ZeroCopyNew<'a>` with zero byte length and leaked `Box` instances

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Areas requiring attention:

The process_input() and process_input_generic() signature changes propagate to callers across the codebase; verify all call sites correctly handle the new Option and InputType return types
Unit-struct handling in zero_copy_eq.rs returns hardcoded true comparisons—confirm this is the intended semantics and doesn't mask actual inequality cases
Mutable reference generation via Box::leak() in zero_copy_mut.rs—verify memory safety guarantees and lifetime management for leaked allocations

Possibly related PRs

feat: zero copy macro #1851 — Parallel PR extending zero-copy-derive macros with UnitStruct support across the same derive paths and function signatures.
feat: zero copy derive enum #1909 — Related input classification extension adding Enum support alongside this PR's UnitStruct, both modifying InputType enum and process functions in shared/utils.rs.

Suggested labels

ai-review

Suggested reviewers

sergeytimoshin
SwenSchaeferjohann

Poem

🎯 A unit struct stands alone, so bare,
Now zero-copy gives it care,
With static refs and aliases lean,
The tiniest type's now part of the scene! ✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 70.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately describes the main change: adding unit struct support to the light zero-copy derive macros.

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment
Commit unit tests in branch jorrit/feat-zero-copy-unit-struct

📜 Recent review details

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 32f0acf and c810abc.

⛔ Files ignored due to path filters (3)

program-tests/zero-copy-derive-test/tests/instruction_data.rs is excluded by none and included by none
program-tests/zero-copy-derive-test/tests/ui/fail/01_empty_struct.stderr is excluded by none and included by none
program-tests/zero-copy-derive-test/tests/ui/pass/01_empty_struct.rs is excluded by none and included by none

📒 Files selected for processing (4)

program-libs/zero-copy-derive/src/shared/utils.rs (3 hunks)
program-libs/zero-copy-derive/src/zero_copy.rs (1 hunks)
program-libs/zero-copy-derive/src/zero_copy_eq.rs (1 hunks)
program-libs/zero-copy-derive/src/zero_copy_mut.rs (1 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

program-libs/zero-copy-derive/**/*.rs

📄 CodeRabbit inference engine (program-libs/zero-copy-derive/README.md)

program-libs/zero-copy-derive/**/*.rs: Apply #[derive(ZeroCopy)] macro to structs to derive ZeroCopyAt trait for zero-copy serialization
Apply #[derive(ZeroCopyMut)] macro to structs to derive ZeroCopyAtMut and ZeroCopyNew traits
Apply #[derive(ZeroCopyEq)] macro to structs to derive PartialEq comparing ZeroCopy representation with original struct
All structs and enums used with ZeroCopy macros must have #[repr(C)] attribute for memory layout safety
Use only supported primitive types: u8, u16, u32, u64, i8, i16, i32, i64, and bool in structs with ZeroCopy macros
Use Vec for collections in zero-copy structs, where T is a supported primitive type or implements ZeroCopyAt trait
Use Arrays [T; N] for fixed-size collections in zero-copy structs where T is a supported type
Use Option for optional values in zero-copy structs; Option, Option, and Option are optimized
Only structs with named fields are supported with ZeroCopy macros; tuple structs are not supported
Structs must have at least one field for zero-copy serialization; empty structs are not supported
ZeroCopyMut and ZeroCopyEq macros only support structs; enums are not supported with these macros
ZeroCopy macro supports enums with unit variants or single unnamed field variants only
Custom types in zero-copy structs must implement the ZeroCopyAt trait
Extract first consecutive fixed-size fields into a meta struct ZMeta; stop extraction at first Vec, Option, or non-Copy type
Primitive integer types are automatically converted to little-endian equivalents (u16→U16, u32→U32, u64→U64) in zero-copy structs
Boolean types are converted to u8 in zero-copy structs for alignment and serialization
Vec uses optimized slice operations in zero-copy structs; other Vec types use ZeroCopySlice
Option, Option, and Option are optimized in zero-copy structs; other Option types delegate to T's ZeroCopyAt implementation
Nested structs in zero-copy serialization must also derive...

Files:

program-libs/zero-copy-derive/src/zero_copy_eq.rs
program-libs/zero-copy-derive/src/shared/utils.rs
program-libs/zero-copy-derive/src/zero_copy_mut.rs
program-libs/zero-copy-derive/src/zero_copy.rs

program-libs/**/*.rs

📄 CodeRabbit inference engine (CLAUDE.md)

Unit tests in program-libs must not depend on light-test-utils; tests requiring light-test-utils must be located in program-tests/

Files:

program-libs/zero-copy-derive/src/zero_copy_eq.rs
program-libs/zero-copy-derive/src/shared/utils.rs
program-libs/zero-copy-derive/src/zero_copy_mut.rs
program-libs/zero-copy-derive/src/zero_copy.rs

🧠 Learnings (19)

📓 Common learnings

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/batched-merkle-tree/docs/CLAUDE.md:0-0
Timestamp: 2025-11-24T17:56:00.229Z
Learning: Applies to program-libs/batched-merkle-tree/docs/**/Cargo.toml : Depend on light-zero-copy crate for zero-copy serialization for efficient account data access

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Apply #[derive(ZeroCopy)] macro to structs to derive ZeroCopyAt trait for zero-copy serialization

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Use Vec<T> for collections in zero-copy structs, where T is a supported primitive type or implements ZeroCopyAt trait

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Apply #[derive(ZeroCopyEq)] macro to structs to derive PartialEq comparing ZeroCopy representation with original struct

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Nested structs in zero-copy serialization must also derive #[derive(ZeroCopy)]

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Structs must have at least one field for zero-copy serialization; empty structs are not supported

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Use Option<T> for optional values in zero-copy structs; Option<u16>, Option<u32>, and Option<u64> are optimized

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Apply #[derive(ZeroCopyMut)] macro to structs to derive ZeroCopyAtMut and ZeroCopyNew traits

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Primitive integer types are automatically converted to little-endian equivalents (u16→U16, u32→U32, u64→U64) in zero-copy structs

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Option<u64>, Option<u32>, and Option<u16> are optimized in zero-copy structs; other Option<T> types delegate to T's ZeroCopyAt implementation

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : ZeroCopy macro supports enums with unit variants or single unnamed field variants only

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Only structs with named fields are supported with ZeroCopy macros; tuple structs are not supported

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Extract first consecutive fixed-size fields into a meta struct Z<StructName>Meta; stop extraction at first Vec, Option, or non-Copy type

Learnt from: CR
Repo: Lightprotocol/light-protocol PR: 0
File: program-libs/zero-copy-derive/README.md:0-0
Timestamp: 2025-11-24T17:54:20.982Z
Learning: Applies to program-libs/zero-copy-derive/**/*.rs : Use only supported primitive types: u8, u16, u32, u64, i8, i16, i32, i64, and bool in structs with ZeroCopy macros