# Migrate a deprecated API across every callsite in WebAssembly with Atlas in 2026 > Atlas helps WebAssembly developers migrate deprecated APIs by enumerating all callsites, applying context-anchored patches, and verifying changes with wasm-pack test. Atlas enables WebAssembly developers to systematically migrate deprecated APIs across every callsite, ensuring no caller is missed. It integrates directly with your existing toolchain, including wasm-pack test, cargo (wasm-bindgen), and rustfmt, to provide a verified, step-by-step migration process in 2026. ## Key takeaways - Atlas uses `lsp` and `grep` to find all WebAssembly API calls, including those in `#[wasm_bindgen]` exports and generated JS glue. - Context-anchored `apply_patch` ensures safe, precise migrations in WebAssembly code, preventing accidental changes to drifted files. - Automated `wasm-pack test --node` verification after each change guarantees functional WebAssembly migrations and prevents regressions. - Atlas's read-only plan agent and unified diffs provide transparent review and explicit approval for all WebAssembly code modifications. - Atlas integrates directly with `cargo (wasm-bindgen)`, `wasm-pack build --target web`, and `rustfmt` for a native WebAssembly development experience. ## How Atlas finds all deprecated WebAssembly API calls Atlas ensures 100% coverage when migrating deprecated WebAssembly APIs by combining two powerful search methods. In 2026, it uses the lsp tool's findReferences for AST-based calls and cross-checks with grep for dynamic or string-based usages, including those within the JavaScript glue generated by wasm-bindgen. To move an entire WebAssembly codebase off a deprecated function or module onto its replacement, Atlas first needs a complete list of every callsite. It achieves this by leveraging the lsp tool's findReferences operation on the deprecated symbol, which provides a robust, language-server-driven enumeration of all direct, AST-declared callers. This is crucial for Rust code compiled to WebAssembly. However, WebAssembly often involves a boundary with JavaScript, where calls might be dynamic or string-based, especially within the JS glue generated by wasm-bindgen. To catch these, Atlas performs a secondary, permission-gated grep search across the codebase. This dual approach guarantees that no callsite, whether explicit in Rust source or implicit in generated JavaScript, is missed, providing a comprehensive enumeration for the migration task. ## Migrating WebAssembly callsites with context-aware patching Migrating deprecated WebAssembly API calls requires precision to avoid introducing new bugs. Atlas ensures this by creating one todowrite entry per callsite, making partial progress visible, and then using apply_patch. This tool seeks the hunk's context and old_lines, failing rather than misapplying to a drifted file, ensuring 100% accuracy. Once all deprecated WebAssembly API calls are identified, Atlas systematically migrates each one. The todowrite tool is used to create a distinct entry for every callsite, transforming the enumeration into a trackable worklist. This ensures that partial progress is visible and no callsite is silently skipped. For the actual migration, Atlas employs the apply_patch tool. This tool is designed for safety and reliability: it doesn't guess. Instead, apply_patch explicitly seeks the hunk's context and the exact old_lines it expects to find. If the file has drifted and these expected lines are not present, apply_patch throws a 'Failed to find expected lines' error. This prevents misapplication of patches to an incorrect or changed location, which is especially important when dealing with the intricate bindings and memory management often found in wasm32-wasip2 target configurations. ## Verifying WebAssembly API migrations with automated tests After each WebAssembly file modification, Atlas immediately verifies the changes to ensure functional correctness. It runs the affected tests using the real wasm-pack test --node command behind a permission prompt, marking the todo entry complete only once tests pass. This iterative verification process is a core safety feature in 2026. A critical step in any API migration, especially in WebAssembly where host interactions and bindings are sensitive, is immediate verification. Atlas integrates directly with your WebAssembly testing workflow. After each individual file is migrated using apply_patch, Atlas executes the affected tests. It does this by calling the bash tool to run the actual WebAssembly test runner command: wasm-pack test --node. This command is run behind a permission prompt, giving you control. Only once these tests pass successfully is the corresponding todowrite entry marked as completed. This ensures that each migration step is functionally sound before proceeding, preventing a cascade of errors and maintaining the integrity of your WebAssembly module. Furthermore, Atlas can then run rustfmt on the diff to ensure consistent code style. ## Ensuring safety and review for WebAssembly API changes Atlas prioritizes safety and transparency throughout the WebAssembly API migration process. It drafts a plan in a read-only plan agent and asks for approval before switching to a build agent. Every Atlas tool call is permission-gated, and a unified diff is computed for every file edit, surfaced for approval before writing, ensuring 100% control in 2026. Migrating a deprecated API across an entire WebAssembly codebase is a significant undertaking, and Atlas is built with multiple layers of safety and review. Before any changes are made, Atlas drafts a comprehensive plan in a read-only plan agent, which you must approve. Every tool call, including lsp, grep, todowrite, apply_patch, and bash, is permission-gated against allow, ask, and deny rules, giving you granular control over Atlas's actions. For every proposed file edit, Atlas computes a unified diff and surfaces it for your explicit approval before writing any changes to disk. This allows you to review exactly what Atlas intends to do. Atlas also reads git branches, status, and diffs, and can stage and create commits on your behalf, ensuring that the entire migration process is transparent, auditable, and integrated into your existing version control workflow. ## Steps 1. 1: Initialize Atlas in your WebAssembly crate: Ensure your Cargo.toml sets crate-type = "cdylib" and depends on wasm-bindgen, then launch Atlas within this project directory. 2. 2: Enumerate all deprecated API calls: Use `atlas lsp findReferences` on the deprecated symbol and `atlas grep` for dynamic usages within your WebAssembly project, including generated JS glue and #[wasm_bindgen] exports. 3. 3: Track each migration task: Create a `todowrite` entry for every identified callsite so that partial progress is visible and nothing is silently skipped during the migration. 4. 4: Apply context-anchored patches: For each `todowrite` entry, use `atlas apply_patch` to migrate the callsite. Atlas will fail with 'Failed to find expected lines' if the context or old lines drift, preventing misapplication to a changed file. 5. 5: Verify changes with WebAssembly tests: After each file modification, run `atlas bash "wasm-pack test --node"` behind a permission prompt to confirm functionality. Mark the `todowrite` entry complete only upon test success. 6. 6: Final cleanup and formatting: After all migrations, `atlas grep` for the deprecated symbol to confirm zero remaining hits, delete the old implementation, and run `atlas bash "rustfmt"` to format the codebase consistently. ## FAQ ### How does Atlas find all WebAssembly API calls, even in JS glue? Atlas combines `lsp findReferences` for AST-based calls in your Rust source with `grep` to catch dynamic or string-based usages, including those within the JavaScript glue generated by `wasm-bindgen` and `#[wasm_bindgen]` exports. ### Can Atlas handle migrations involving `wasm32-wasip2` targets? Yes, Atlas is designed to operate within crates configured for `wasm32-wasip2` targets, understanding the specific bindings, memory interactions, and host boundary considerations inherent to WebAssembly. ### What if my WebAssembly code has drifted since the patch was generated? Atlas's `apply_patch` tool is context-anchored. If the expected old lines or surrounding context have changed, it will report 'Failed to find expected lines' rather than applying a potentially incorrect patch, ensuring code safety. ### How does Atlas ensure my WebAssembly tests pass after a migration? After each file is modified, Atlas can run `wasm-pack test --node` via a `bash` tool call. The migration step is only marked complete once these tests pass, ensuring functional correctness of your WebAssembly module. ### Does Atlas integrate with `rustfmt` for WebAssembly projects? Absolutely. Atlas can execute `rustfmt` via its `bash` tool to ensure all code changes adhere to your project's formatting standards, maintaining consistency across your WebAssembly codebase after migrations. ### How does Atlas prevent unintended changes to my WebAssembly project? Atlas employs a read-only plan agent, permission-gated tool calls, and presents a unified diff for every proposed file edit, requiring your explicit approval before writing any changes to your WebAssembly files. ### Can Atlas help move a hot loop across the WebAssembly boundary? Yes, Atlas can assist in refactoring hot loops to move across the WebAssembly boundary, optimizing for single calls instead of chatty per-element interactions through JavaScript, improving performance for your WebAssembly module. --- Canonical HTML: https://runatlas.sh/resources/stacks/migrate-a-deprecated-api-across-callsites-in-webassembly Source of truth: aeo_pages row `/resources/stacks/migrate-a-deprecated-api-across-callsites-in-webassembly` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.