Error adding Custom RPCs for custom pallet Substrate

Question

I've been working with parity's contracts node (latest version) and the substrate template node (tag polkadot-v0.9.18), both present the same issue when compiling.

I have a very simple pallet that stores certain items. The main structure is the following:

#[pallet::storage]
#[pallet::getter(fn items)]
/// 'Mapping' Item ID -> Item Data
pub(crate) type Items<T: Config> = StorageMap<_, Twox64Concat, T::Hash, Item<T>>;

I was trying to add a simple RPC method following this guides https://core.tetcoin.org/recipes/custom-rpc.html#rpc-to-call-a-runtime-api and https://core.tetcoin.org/recipes/runtime-api.html

I also checked some projects that already have custom RPC calls implementations, like de subsocial node and I have pretty much the same structure and dependencies.

My rpc method does nothing but return a number 2 just to make sure it works, but it doesn't. This is what the pallets directory looks like: pallets directory

When I try to compile, the following error shows

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

I don't even use that module, but I've read that it is used somewhere as an indirect dependency. I'm compiling my project with the following command

cargo build --release

Checking the documentation regarding the 'getrandom' crate issue, I added the following dependency in the Cargo.toml (I tried adding it in every Cargo.toml within the project, individually, by pairs, ...)

getrandom = { version = "0.2", features = ["js"] }

Then another error shows up:

error: failed to run custom build command for secp256k1-sys v0.4.1

Which again, doesn't make any sense to me. The project itself has nothing but the node template base and a new pallet that implements a create and transfer function. Without the RPC implementation, it works perfectly using the Polkadot App, but as soon as I include the custom rpc, it just doesn't compile.

This is my rust configuration (rustup show)

 installed toolchains
 --------------------

 stable-x86_64-apple-darwin (default)
 nightly-2021-11-04-x86_64-apple-darwin
 nightly-x86_64-apple-darwin

 active toolchain
 ----------------

 stable-x86_64-apple-darwin (default)
 rustc 1.59.0 (9d1b2106e 2022-02-23)

I haven't found anyone who is dealing with this kind of issue, and I don't know where the problem might be.

This is the first issue logs:

  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
     --> /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.5/src/lib.rs:229:9
      |
  229 | /         compile_error!("the wasm32-unknown-unknown target is not supported by \
  230 | |                         default, you may need to enable the \"js\" feature. \
  231 | |                         For more information see: \
  232 | |                         https://docs.rs/getrandom/#webassembly-support");
      | |________________________________________________________________________^

  error[E0433]: failed to resolve: use of undeclared crate or module `imp`
     --> /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.5/src/lib.rs:256:5
      |
  256 |     imp::getrandom_inner(dest)
      |     ^^^ use of undeclared crate or module `imp`

  For more information about this error, try `rustc --explain E0433`.
  error: could not compile `getrandom` due to 2 previous errors
  warning: build failed, waiting for other jobs to finish...
  error: build failed

Current status (to reproduce error): https://github.com/andresvsm/substrate-pallet-rpc/tree/items-branch

Answer 1

Sometimes, you can get this error from a deep dependency of another dependency, e.g. when you really build for a wasm32-unknown-unknown target, and getrandom is linked but even not used. It can be fixed (worked around) with the following trick:

In Cargo.toml, add this line:

[dependencies]
getrandom = {version = "0.2", default-features = false, features = ["custom"]}

It tells the compiler to use a dummy implementation inside of getrandom.