Atlas helps WebAssembly developers in 2026 restructure legacy modules without breaking callers by mapping public surfaces with LSP, pinning behavior with `wasm-pack test`, and applying changes with `apply_patch` while tracking progress with `todowrite`.
How Atlas Maps WebAssembly Module Public Surfaces
To refactor a WebAssembly module without breaking its callers, Atlas first maps the module's public surface using its `lsp` tool. This process identifies all `#[wasm_bindgen]` exports and their corresponding JavaScript glue, ensuring no public API is overlooked during the 2026 refactoring effort.
Atlas begins a WebAssembly refactor by leveraging its `lsp` tool to perform a `documentSymbol` operation on your Rust source files. This identifies all public functions and structures, specifically targeting those annotated with `#[wasm_bindgen]` that define the module's interface to JavaScript. Once these symbols are mapped, Atlas then uses `findReferences` on each exported symbol. This crucial step enumerates every callsite, both within the Rust crate and, importantly, in the generated JavaScript glue code. By understanding how the WebAssembly module is consumed, Atlas ensures that any structural changes made during the refactor will not silently break existing integrations. This comprehensive mapping prevents unexpected runtime errors in your host environment.
Pinning WebAssembly Module Behavior with `wasm-pack test`
Before any code changes, Atlas establishes a green baseline for your WebAssembly module's behavior. It executes your existing tests using `wasm-pack test --node` via its `bash` tool, recording the initial state. This ensures that the refactor, which begins in 2026, maintains the module's original functionality without introducing regressions.
A critical first step in any safe refactor is pinning the existing behavior. For WebAssembly modules, Atlas achieves this by running your test suite. It uses its `bash` tool to execute `wasm-pack test --node`, targeting the `wasm32-wasip2` environment if configured, or the standard `web` target. This command runs your Rust tests compiled to WebAssembly within a Node.js environment, providing a robust verification of the module's current functionality. Atlas records the output, establishing a 'green baseline.' This baseline serves as the immutable reference point throughout the refactoring process. Any subsequent change must pass these same tests, guaranteeing that the module's external behavior remains identical, even as its internal structure evolves.
Applying Structural Changes to WebAssembly with `apply_patch`
Atlas applies structural changes to your WebAssembly module using its `apply_patch` tool, which anchors on context lines to ensure precise modifications. This method prevents accidental changes to drifted files, a common risk in 2026 development. Each hunk is applied individually, maintaining control and safety.
Once the public surface is mapped and behavior is pinned, Atlas proceeds with the actual restructuring. It uses its `apply_patch` tool to make structural changes. This tool is designed for safety: it seeks each hunk's context and `old_lines` within the target file. If the file has drifted or changed unexpectedly since the patch was generated, `apply_patch` will fail with a 'Failed to find context' error, preventing a potentially destructive modification. This ensures that Atlas only applies changes to the exact code it expects. For WebAssembly projects, this means safely refactoring Rust source files within your `crate-type cdylib` project, ensuring that the underlying WebAssembly output remains consistent with the intended behavior.
Iterative Testing and Formatting for WebAssembly Refactors
Atlas re-runs `wasm-pack test --node` after each `apply_patch` hunk lands, not just once at the end. This iterative approach provides immediate feedback on behavior, catching regressions early. Additionally, Atlas uses `rustfmt` to ensure code consistency, even for complex refactors in 2026.
To maintain a high level of confidence during a WebAssembly refactor, Atlas adopts an iterative testing strategy. After each individual hunk is applied by `apply_patch`, Atlas immediately re-runs the tests using `bash` to execute `wasm-pack test --node`. This frequent validation ensures that any introduced regression is caught as soon as it occurs, making debugging significantly easier. Furthermore, Atlas integrates with `rustfmt` to automatically format the code changes. After applying a patch and re-running tests, Atlas can prompt to run `rustfmt` on the modified files, ensuring that the refactored code adheres to your project's style guidelines and maintains a clean, readable diff for approval. This combination of continuous testing and automated formatting streamlines the refactoring workflow for WebAssembly projects.
Tracking WebAssembly Call Sites with `todowrite`
Atlas uses its `todowrite` tool to track remaining call sites that need migration after a partial WebAssembly module refactor. This ensures that no callers are forgotten, preventing silent breakage. The list provides a clear, actionable plan for completing the refactor in 2026.
Refactoring a large WebAssembly module often involves migrating callers incrementally. Atlas addresses this challenge with its `todowrite` tool. After identifying all call sites using `lsp findReferences`, Atlas can generate a `todowrite` list for any remaining callers that still need to be updated to the new module interface. This list acts as a persistent, actionable checklist, ensuring that a partially migrated module cannot be mistaken for a finished one. It provides a clear overview of the outstanding work, allowing developers to systematically address each call site, whether it's in the JavaScript host environment or other Rust modules consuming the WebAssembly output. This prevents silent breakage and ensures a complete, verified refactor.
Step by step
- 01Run Atlas in your WebAssembly crate, ensuring `Cargo.toml` sets `crate-type cdylib` and depends on `wasm-bindgen`.
- 02Ask Atlas to map the module's public surface using `lsp documentSymbol` on `#[wasm_bindgen]` exports, then `findReferences` on each exported symbol to enumerate all JS glue and Rust callsites.
- 03Pin behavior by having Atlas run `bash wasm-pack test --node` to record a green baseline of your existing WebAssembly tests.
- 04Instruct Atlas to restructure the module using `apply_patch`, which anchors on context lines and refuses to apply against a drifted file.
- 05After each `apply_patch` hunk lands, have Atlas re-run `bash wasm-pack test --node` to verify behavior immediately.
- 06Ask Atlas to run `rustfmt` on the modified files to ensure consistent formatting and a clean diff.
- 07Track any remaining callsites that need migration in a `todowrite` list, ensuring a complete refactor of your WebAssembly module.
Frequently asked questions
- How does Atlas ensure my WebAssembly module's behavior doesn't change?
- Atlas pins your WebAssembly module's behavior by running `wasm-pack test --node` via its `bash` tool before any refactoring. It records this 'green baseline' and re-runs the tests after each change, ensuring no regressions are introduced.
- Can Atlas refactor `#[wasm_bindgen]` exports and their JavaScript glue?
- Yes, Atlas uses its `lsp` tool to identify `#[wasm_bindgen]` exports and then `findReferences` to enumerate all their call sites, including the generated JavaScript glue. This ensures all dependencies are considered during the refactor.
- What if my WebAssembly source file changes while Atlas is working?
- Atlas uses `apply_patch` for structural changes. This tool anchors on context lines and `old_lines`. If the target file has drifted or changed unexpectedly, `apply_patch` will fail with 'Failed to find context', preventing unintended modifications.
- Does Atlas support `wasm-pack build --target web` and `.d.ts` checks?
- Yes, Atlas can be instructed to build your WebAssembly module with `wasm-pack build --target web` and can help check the emitted `.d.ts` files against your JavaScript call sites to ensure type compatibility after refactoring.
- How does Atlas help manage a large WebAssembly refactor with many callers?
- Atlas uses its `todowrite` tool to track remaining call sites that need migration. After identifying all references with `lsp findReferences`, it can generate a list of outstanding tasks, ensuring no callers are forgotten during a phased refactor.
- Can Atlas format my Rust code after refactoring a WebAssembly module?
- Absolutely. Atlas can run `rustfmt` on the modified Rust source files after applying patches. This ensures that your refactored WebAssembly module's code adheres to your project's formatting standards and maintains readability.
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