[Roadmap] Mutative v2

[unadlib]

Goal

Mutative v2 will focus on correctness, performance, smaller package output, and a better developer experience.

Correct by default. Faster when safe. Smaller and easier to adopt.

Plan

Core semantics

• Improve shared-reference handling in nested create() calls.
• Align with Immer where appropriate and document intentional differences.
• Ensure enabling patches never changes the final state.
• Verify that patches reproduce the result and inverse patches restore the original state.
• Add coverage for shared references, nested drafts, sparse arrays, and complex array mutations.

Array performance

• Use the conservative array implementation when patches are enabled.
• Enable specialized array fast paths when patches are disabled.
• Optimize high-impact operations such as shift(), unshift(), splice(), and reverse().
• Ensure optimized and conservative paths always produce identical results.
• Prevent performance regressions in sequential reads and full-array traversal.

Benchmarks

• Build reproducible benchmarks for Mutative v1, Mutative v2, and a pinned Immer version.
• Measure patch-enabled and patch-disabled modes separately.
• Cover mutation-heavy, read-heavy, small-state, and large-state workloads.
• Track execution time, memory usage, and common array operations.
• Add performance regression budgets to CI.

Build system and bundle size

• Migrate the build system from Rollup to tsdown.
• Preserve existing ESM, CommonJS, UMD, development, and production outputs.
• Preserve package exports and TypeScript declaration compatibility.
• Configure the build target and platform explicitly.
• Validate package output with publint and attw.
• Reduce bundle size and add size regression checks.
• Verify the final packed npm artifact before release.

Tooling

• Upgrade pnpm and regenerate the lockfile.
• Migrate the test suite from Jest to Vitest.
• Preserve test behavior, coverage, mocks, snapshots, and timer semantics.
• Update CI and the build environment for tsdown.
• Keep tooling migrations separate from runtime changes.

Website and documentation

• Refactor the website.
• Add first-class Chinese language support.
• Publish v2 benchmarks and methodology.
• Add a v1-to-v2 migration guide.
• Document patch behavior and important differences from Immer.
• Keep the website refactor independent from the core runtime release.

Real-world validation

• Test v2 in representative applications before the stable release.
• Verify ESM, CommonJS, TypeScript, bundler, and supported Node.js compatibility.
• Collect beta feedback and resolve correctness or compatibility blockers.
• Define a maintenance window for Mutative v1.