the wasm32-unknown-unknown target is not supported by default

Question

I am attempting to implement a custom pallet, but I keep running into this compile error:

error: the wasm32-unknown-unknown target is not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
     --> /Users/jackson/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.7/src/lib.rs:235:9
      |
  235 | /         compile_error!("the wasm32-unknown-unknown target is not supported by \
  236 | |                         default, you may need to enable the \"js\" feature. \
  237 | |                         For more information see: \
  238 | |                         https://docs.rs/getrandom/#webassembly-support");
      | |________________________________________________________________________^

  error[E0433]: failed to resolve: use of undeclared crate or module `imp`
     --> /Users/jackson/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.7/src/lib.rs:262:5
      |
  262 |     imp::getrandom_inner(dest)
      |     ^^^ use of undeclared crate or module `imp`

I have found a few other posts related to this but I haven't found an answer with a connection to the pallets. If I omit the custom pallet, then everything builds fine. Has anyone seen this issue before?

Answer 1

Pallets compile to WASM which means that all dependencies need to work in a no-std environment.
In your case it looks like one of your dependencies tries to generate rangom numbers.
This does not work in WASM and the dependency therefore prints that it cannot build.
There are a few cases where this can easily be fixed:

• Add the dependency as dev dependency if you only need it in tests.
• Use the proper way to generate randomness on-chain.
• Use cargo tree to find out how the randomness dependency ends up in your pallet if you dont intend to use it.
• Analyze the offending dependency and see if it even supports no-std.

In any way; it always helps if you share the code. But hopefully this gives you a hint!

Answer 2

Make sure your newly added substrate dependency have default-features = false

Answer 3

I've just solved the same issue. In my case it was an extra dependency in a custom pallet. After removing frame-benchmarking = { version = "4.0.0-dev", path = "../../frame/benchmarking" } from Cargo.toml it compiled.

Answer 4

If you are sure that your std configuration is correct.

Take a look at https://github.com/paritytech/substrate/pull/10837. You may need to cherry-pick this one.

Answer 5

Removing Cargo.lock file and changing optional = true to false in Cargo.toml frame-benchmarking's entry worked for me.