In 2026, Atlas helps WebAssembly developers debug a single failing test by running `wasm-pack test` in isolation, analyzing the code with `lsp`, and proposing precise fixes to the underlying Rust source, not the assertion. This process leverages Atlas's deep understanding of your `Cargo.toml` configuration and `#[wasm_bindgen]` exports to address issues at the crucial WebAssembly boundary.
How does Atlas debug a single WebAssembly test?
Atlas debugs a single WebAssembly test by first executing `wasm-pack test` with a specific filter flag, ensuring only the relevant test runs. This focused approach reduces output noise by over 90%, allowing Atlas to quickly identify the failure point and begin its analysis in 2026.
Atlas initiates the debugging process by invoking its `bash` tool to run `wasm-pack test --node --test <test_name>` within your WebAssembly crate. This command, familiar to any Rustacean working with WebAssembly, isolates the failing test. Atlas then uses its `read` tool to examine the test's assertion and the Rust module it exercises. Leveraging its `lsp` tool, which understands your `#[wasm_bindgen]` exports and the generated JS glue, Atlas walks the call graph from the test through your Rust code, paying close attention to memory management and data transfer across the WebAssembly boundary. This deep understanding, built from indexing your code by AST declarations using tree-sitter, allows Atlas to form a precise hypothesis about the root cause of the failure, often related to how host data is handled or how a hot loop crosses the boundary.
What WebAssembly commands and files does Atlas use for debugging?
Atlas uses concrete WebAssembly commands like `wasm-pack test` and `rustfmt`, along with critical files such as `Cargo.toml` and Rust source files containing `#[wasm_bindgen]` attributes, to debug issues. It specifically targets the `wasm32-wasip2` configuration and understands the JS glue generated for your exports, providing a 360-degree view of your project.
For debugging WebAssembly, Atlas directly interacts with your project using the standard Rust and WebAssembly toolchain. It runs `wasm-pack test --node` to execute tests, specifically filtering to run a single test. When proposing fixes, Atlas understands the implications for your `Cargo.toml` file, especially `crate-type cdylib` and `wasm-bindgen` dependencies. It reads your Rust source files, recognizing `#[wasm_bindgen]` macros that define the WebAssembly boundary. After making code changes, Atlas can invoke `rustfmt` to ensure code style consistency, just as a developer would. Atlas also considers the `wasm32-wasip2` target configuration and the `.d.ts` files emitted by `wasm-pack build --target web`, ensuring that any proposed code changes align with the expected JavaScript call sites and the host environment's capabilities.
How does Atlas ensure safe and reviewable WebAssembly code fixes?
Atlas ensures safe and reviewable WebAssembly code fixes by drafting a plan in a read-only agent, asking for permission before executing any tool, and presenting a unified diff for every file edit. This multi-stage approval process, involving at least 2 distinct review points, guarantees transparency and developer control over changes to your Rust and WebAssembly codebase.
Atlas prioritizes safety and developer oversight throughout the debugging and fixing process. Before making any changes, Atlas drafts a detailed plan in a read-only plan agent, outlining its proposed steps to fix the WebAssembly code. This plan is presented to you for approval. Every Atlas tool call, including `edit` or `apply_patch` to modify Rust source files or `bash` to re-run `wasm-pack test`, is permission-gated against allow, ask, and deny rules. When Atlas proposes an `edit`, it computes a unified diff for the file change and surfaces it for your explicit approval before writing. For larger, multi-hunk changes, Atlas can use `apply_patch`, which also generates a clear diff for review. Furthermore, Atlas snapshots file changes as git patches, allowing edits to be easily diffed, rolled back, or staged and committed on your behalf, providing robust version control integration for your WebAssembly project.
Step by step
- 01Run the failing WebAssembly test in isolation: Use Atlas's `bash` tool to execute `wasm-pack test --node --test <your_failing_test_name>` to isolate the specific test causing issues in your WebAssembly project.
- 02Analyze the test and walk the call graph: Employ Atlas's `read` tool to examine the failing test's assertion and the Rust module it exercises. Then, use the `lsp` tool's `goToDefinition` and `findReferences` operations to trace the call path through your `#[wasm_bindgen]` exports and into the core WebAssembly logic.
- 03Form a hypothesis and verify with temporary logging: Based on the call graph analysis, form a hypothesis about the bug. Use Atlas's `edit` tool to insert temporary `log::debug!` statements into your Rust code, or re-run `wasm-pack test` with a verbose flag via `bash` to gather more information about the WebAssembly runtime behavior.
- 04Fix the production WebAssembly code: Once the root cause is identified, use Atlas's `edit` tool to apply precise fixes to the Rust source code. If the change spans multiple hunks or is complex, instruct Atlas to use `apply_patch` for a more robust and reviewable modification to your WebAssembly module.
- 05Re-run tests and clean up: After fixing the code, use `bash` to re-run the single failing `wasm-pack test` to confirm the fix. Then, run the full `wasm-pack test` suite to ensure no regressions. Finally, use Atlas's `edit` tool to remove any temporary logging or debugging flags added in the previous step.
- 06Format the code: Have Atlas run `rustfmt` on the modified files via `bash` to ensure all changes adhere to your project's code style guidelines for your WebAssembly crate.
Frequently asked questions
- How does Atlas handle WebAssembly memory and bindings issues?
- Atlas is specifically designed to understand the WebAssembly boundary. It reads your `#[wasm_bindgen]` exports and the generated JavaScript glue, allowing it to identify and help fix issues related to memory management, data transfer, and host interactions within your Rust code.
- Can Atlas debug a specific `wasm-pack test` in a large WebAssembly project?
- Yes, Atlas uses the `bash` tool to execute `wasm-pack test --node --test <test_name>`, allowing it to run only the specified failing test. This significantly reduces the output and focuses the debugging effort on the relevant WebAssembly code.
- What if my WebAssembly test failure is due to a complex interaction with JavaScript?
- Atlas understands the `.d.ts` files emitted by `wasm-pack build --target web` and the JS glue. It can analyze how your Rust functions are called from JavaScript and vice-versa, helping to pinpoint issues at the WebAssembly binding layer.
- How does Atlas ensure my WebAssembly code changes are formatted correctly?
- After making code edits, Atlas can invoke `rustfmt` via its `bash` tool. This ensures that any modifications to your Rust source files, including those with `#[wasm_bindgen]` attributes, adhere to your project's established formatting standards.
- Does Atlas support debugging WebAssembly on different targets like `wasm32-wasip2`?
- Yes, Atlas is aware of your `wasm32-wasip2` target configuration. It considers this context when analyzing your code and proposing fixes, ensuring compatibility with your specific WebAssembly environment.
- How does Atlas prevent me from accidentally accepting a bad fix for my WebAssembly code?
- Atlas employs a multi-stage safety mechanism. It first drafts a plan in a read-only agent, then asks for permission before running any tool. Crucially, every code edit is presented as a unified diff for your explicit approval before it's written to your WebAssembly project files.
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