Rust 1.96: WebAssembly reports missing symbols earlier

Move an error into the build

Our retrospective May review highlights Rust 1.96, released on May 28, 2026. WebAssembly targets no longer add --allow-undefined to the linker: undefined symbols now produce a link error. Rust announcement.

Describe the contract with the host

A module targeting a browser or another execution environment sometimes depends on functions supplied by that host. For developers, a build failure offers a checkpoint before delivery: is this function expected, correctly named and actually available? The goal is documenting the exchange between both sides rather than discovering a forgotten dependency when the module loads.

Examine errors before changing options

During an upgrade, every newly missing symbol therefore deserves identification. It may represent an intentional contract or an error in how the project is assembled. The response should follow that distinction. Building the module remains only one step: a trial in the intended host must still check imports, startup and a representative workflow, particularly for a web application or game export.