Zig Java Migration

Java to Zig Migration

Treat migration as preservation of observable contracts, not translation of syntax or production-file counts. Java remains the compatibility oracle until the complete agreed denominator is proven in Zig.

Compose with the Zig skill pack

This skill owns migration governance. Load the target-language skills needed by the repository instead of embedding a second Zig manual here:

• use $zig-0.16 for Zig 0.16 projects and $zig-0.15 only when the pinned toolchain requires it;
• use $zig-project-structure and $zig-build-system for modules, build.zig, package paths, targets, and cross-compilation;
• use $zig-testing and $zig-java-migration-testing for test implementation and completion evidence;
• use $zig-concurrency, $zig-json, $zig-http, or $zig-crypto only when those contracts are in scope;
• finish with $zig-code-review and $zig-tiger-style where compatible with source parity.

The source-side migration contract is shared with rust-java-migration and future kotlin-java-migration and swift-java-migration skills. Only the target-language profile changes. Read Cross-language migration profile before changing denominators, dispositions, document schemas, or completion claims.

Non-negotiable outcome

A completed migration has all of the following:

1. Every in-scope Java object, member, overload, parameter, exception, comment, test case, fixture, script, example, and externally observable behavior has a traceable Zig disposition.
2. Every required disposition has real Zig logic; declarations, imports, generated API lists, empty bodies, unreachable, placeholder errors, and compile-only facades do not count.
3. The complete Java test suite and the complete Zig lossless-port suite pass.
4. Every concrete source case has a Java/Zig golden or live differential result of MATCH; no mismatch, harness failure, skip, or not-run case remains.
5. Zig-specific allocator, ownership, error-set, defer/errdefer, target, ABI, concurrency, and build-graph risks have additional tests.
6. Real-host, load, security, rollout, and rollback claims remain separate from functional parity and require their own evidence.

Coverage is a diagnostic signal. It is never the migration denominator or proof that Java and Zig produce the same result.

Establish baselines and scope

Record before editing:

• immutable Java SHA/tag and Zig SHA;
• JDK/build-tool versions, Zig version, target triple, optimization mode, and build options;
• source and target roots;
• public API, serialization, protocol, error, lifecycle, concurrency, and side effect contracts;
• source test roots and every non-standard fixture/resource/script/data root;
• generated sources, platform-only behavior, approved exclusions, and blockers;
• exact commands for Java, Zig, differential, host, and non-functional gates.

If .codegraph/ exists, use CodeGraph before text search to trace public entry points, dynamic registries, callbacks, lifecycle edges, and test-to-production paths. Otherwise use deterministic source inventories and compiler/build data.

Maintain four current migration documents

Keep one current set per source module:

1. 迁移路线图.md
2. 对象级对照表.md
3. 语义迁移对照表.md
4. 对象名称一致性检查.md

All four documents must carry the same Java baseline, Zig baseline, audit date, scope, and completion state. Historical design material belongs after an explicit historical marker; it cannot override current generated facts.

Use these states precisely:

Map Java structure to Zig

Default structural rule:

• one Java class/interface/enum/record/annotation maps to one primary .zig file;
• nested types and builders may remain with their owning type;
• package directories become snake_case directories using the documented repository path algorithm;
• root.zig files define module imports and public re-exports, not a warehouse of migrated objects;
• type names use TitleCase; functions and local values use Zig camelCase; preserve Java member names separately in registries, serializers, protocols, or compatibility metadata when observable;
• do not use one compat.zig, generated registry, or re-export facade to inflate object completion.

Preserve Java method parameters in order and meaning. Zig API naming may be idiomatic, but the object and semantic ledgers must record the exact Java symbol to Zig symbol mapping. Read Java-to-Zig semantic mappings before implementing ownership, exceptions, async behavior, generics, reflection, annotations, serialization, or service discovery.

Implement in dependency batches

1. Freeze the complete object, method, test, and asset denominator.
2. Resolve architecture-wide decisions: allocator ownership, error model, cancellation, serialization, registry/SPI, synchronization, and ABI.
3. Implement the full dependency-ordered batch without alternating migration and final acceptance object by object.
4. Recompute the full inventory from current Java and Zig sources.
5. Reconcile all four documents in one pass.
6. Run the unified engineering and semantic verification pipeline.

Avoid permanent compatibility layers that merely preserve Java class shapes. Use Zig-native structs, tagged unions, error unions, comptime, explicit allocators, and modules where they preserve the same contract. Keep adapters at real Java compatibility boundaries such as serialized names, plugin IDs, protocol fields, or host APIs.

Dependency replacement

Do not select a Zig package because its name resembles a Java library. Record:

• exact Java responsibility and observable contract;
• candidate package URL, version/commit, license, Zig compatibility, target support, maintenance and security evidence;
• exact upstream symbol and local call point;
• adapter behavior for errors, lifecycle, cancellation, threading, ordering, allocation, and serialization;
• focused spike, shared conformance test, and real-host result;
• rollback or replacement strategy.

DEPENDENCY_REUSED is valid only after the exact declared dependency path is executed through local integration tests.

Whole-project acceptance module

Every repository/product-level completion claim requires a dedicated, non-production <project>-test/ module. Register an explicit zig build migration-test step in build.zig; keep the module out of published package paths and production artifacts. It owns:

• complete source-suite and immutable source-asset replay;
• public cross-module and binding/adapter workflows;
• Java/Zig golden or live differential execution;
• aggregate machine-readable evidence.

Local test blocks inside production modules prove focused implementation behavior only. They do not replace <project>-test. The whole-project gate is all source cases MATCH with zero failed, skipped, ignored, or not-run cases.

Unified verification

Run after the batch is frozen:

1. formatting and repository-specific lint/style checks;
2. zig build, zig build test, explicit target/optimization matrices, and cross-compilation checks;
3. complete mirrored source tests in <project>-test;
4. complete pinned Java and Zig suites plus every-case differential comparison;
5. real script/example replay;
6. allocator/leak, lifecycle, concurrency, cancellation, and deterministic scheduling tests;
7. malformed input, fuzz/property, load/soak, and security tests;
8. real host/binding/ABI integration;
9. gray rollout and rollback rehearsal when production replacement is claimed.

Read Verification and acceptance for evidence levels and completion reporting.

Red lines

• Do not simplify Java semantics to make Zig implementation easier.
• Do not omit overloads, parameter variants, exception behavior, side effects, lifecycle rules, tests, resources, or comments from the denominator.
• Do not count file existence, imports, exports, build success, or API manifests as implementation.
• Do not use unreachable, placeholder errors, empty tests, or ignored errors as migrated logic.
• Do not treat allocator leaks, borrowed-slice lifetime changes, error-set collapse, target omissions, or ABI changes as internal details.
• Do not modify copied source fixtures in place; preserve byte-identical copies and generate target-specific derivatives separately.
• Do not accept two independently green suites as parity.
• Do not use sampled differential cases, pass thresholds, coverage percentages, or “representative” scripts for a completion claim.
• Do not hide MISSING, PARTIAL, STUB, MISPLACED, or UNVERIFIED rows in historical appendices or alternate documents.

Completion criteria

• The current object denominator contains no incomplete state.
• Every Java object/member/test/case/asset is traceable and losslessly handled.
• Every copied source asset has matching SHA-256.
• Java and Zig complete suites pass from pinned baselines.
• Full per-case differential output is 100% MATCH with zero harness failure or not-run case.
• <project>-test owns the complete command and aggregate artifact.
• Zig-specific allocator, error, target, ABI, concurrency, and build obligations pass.
• Real-host and production-readiness claims have separate evidence.
• Final reporting distinguishes structural, implementation, behavioral, integration, and production-readiness completion.

Resources

• Cross-language migration profile
• Java-to-Zig semantic mappings
• Verification and acceptance
• Migration roadmap template
• Object mapping template
• Semantic mapping template
• Name consistency template