`wasm-snip` replaces a WebAssembly function's body with an `unreachable`
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tests Add a flag to automatically remove all panicking infrastructure Apr 24, 2018
Cargo.toml Update parity-wasm requirement from 0.34.0 to 0.35.0 Oct 17, 2018



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wasm-snip replaces a WebAssembly function's body with an unreachable.

Maybe you know that some function will never be called at runtime, but the compiler can't prove that at compile time? Snip it! Then run wasm-gc again and all the functions it transitively called (which could also never be called at runtime) will get removed too.

Very helpful when shrinking the size of WebAssembly binaries!

This functionality relies on the "name" section being present in the .wasm file, so build with debug symbols:

debug = true


To install the wasm-snip executable, run

$ cargo install wasm-snip

You can use wasm-snip to remove the annoying_space_waster function from input.wasm and put the new binary in output.wasm like this:

$ wasm-snip input.wasm -o output.wasm annoying_space_waster

For information on using the wasm-snip executable, run

$ wasm-snip --help
Replace a wasm function with an `unreachable`.

wasm-snip [FLAGS] [OPTIONS] <input> [--] [function]...

-h, --help                        Prints help information
--snip-rust-fmt-code          Snip Rust's `std::fmt` and `core::fmt` code.
--snip-rust-panicking-code    Snip Rust's `std::panicking` and `core::panicking` code.
-V, --version                     Prints version information

-o, --output <output>         The path to write the output wasm file to. Defaults to stdout.
-p, --pattern <pattern>...    Snip any function that matches the given regular expression.

<input>          The input wasm file containing the function(s) to snip.
<function>...    The specific function(s) to snip. These must match exactly. Use the -p flag for fuzzy matching.


To use wasm-snip as a library, add this to your Cargo.toml:

# Do not build the executable.
default-features = false

See docs.rs/wasm-snip for API documentation.


Licensed under either of

at your option.


See CONTRIBUTING.md for hacking.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.