Duplicate Lang Error When Adding Custom RPC

Question

I am trying to add a custom rpc in Substrate, but I ran into a problem.

I have done all steps in this article:

Add custom RPC to the node

and my code is here:

https://github.com/dortajkianoush/substrate_rpc

but it shows me this error:

error: duplicate lang item in crate `sp_io` (which `sp_application_crypto` depends on): `panic_impl`.
    |
    = note: the lang item is first defined in crate `sp_io` (which `frame_support` depends on)
    = note: first definition in `sp_io` loaded from /home/kianoush/projects/substrate_rpc/target/debug/wbuild/node-template-runtime/target/wasm32-unknown-unknown/release/deps/libsp_io-ff5bbb618e892e0d.rmeta
    = note: second definition in `sp_io` loaded from /home/kianoush/projects/substrate_rpc/target/debug/wbuild/node-template-runtime/target/wasm32-unknown-unknown/release/deps/libsp_io-c5af71db43952901.rmeta

  error: duplicate lang item in crate `sp_io` (which `sp_application_crypto` depends on): `oom`.
    |
    = note: the lang item is first defined in crate `sp_io` (which `frame_support` depends on)
    = note: first definition in `sp_io` loaded from /home/kianoush/projects/substrate_rpc/target/debug/wbuild/node-template-runtime/target/wasm32-unknown-unknown/release/deps/libsp_io-ff5bbb618e892e0d.rmeta
    = note: second definition in `sp_io` loaded from /home/kianoush/projects/substrate_rpc/target/debug/wbuild/node-template-runtime/target/wasm32-unknown-unknown/release/deps/libsp_io-c5af71db43952901.rmeta

  error[E0277]: the trait bound `sp_runtime::generic::Block<sp_runtime::generic::Header<u32, sp_runtime::traits::BlakeTwo256>, sp_runtime::generic::UncheckedExtrinsic<MultiAddress<AccountId32, ()>, RuntimeCall, MultiSignature, (CheckNonZeroSender<Runtime>, CheckSpecVersion<Runtime>, CheckTxVersion<Runtime>, CheckGenesis<Runtime>, CheckEra<Runtime>, CheckNonce<Runtime>, CheckWeight<Runtime>, ChargeTransactionPayment<Runtime>)>>: sp_runtime::traits::Block` is not satisfied
     --> /home/kianoush/projects/substrate_rpc/runtime/src/lib.rs:403:7
      |
  403 |     impl pallet_template_runtime_api::TemplateApi<Block> for Runtime {
      |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `sp_runtime::traits::Block` is not implemented for `sp_runtime::generic::Block<sp_runtime::generic::Header<u32, sp_runtime::traits::BlakeTwo256>, sp_runtime::generic::UncheckedExtrinsic<MultiAddress<AccountId32, ()>, RuntimeCall, MultiSignature, (CheckNonZeroSender<Runtime>, CheckSpecVersion<Runtime>, CheckTxVersion<Runtime>, CheckGenesis<Runtime>, CheckEra<Runtime>, CheckNonce<Runtime>, CheckWeight<Runtime>, ChargeTransactionPayment<Runtime>)>>`
      |
      = help: the trait `sp_runtime::traits::Block` is implemented for `sp_runtime::generic::block::Block<Header, Extrinsic>`
  note: required by a bound in `TemplateApi`
     --> /home/kianoush/projects/substrate_rpc/pallets/template/rpc/runtime-api/src/lib.rs:5:1
      |
  5   | / sp_api::decl_runtime_apis! {
  6   | |     pub trait TemplateApi {
  7   | |         fn get_value() -> u32;
  8   | |     }
  9   | | }
      | |_^ required by this bound in `TemplateApi`
      = note: this error originates in the macro `sp_api::decl_runtime_apis` (in Nightly builds, run with -Z macro-backtrace for more info)

  For more information about this error, try `rustc --explain E0277`.
  error: could not compile `node-template-runtime` due to 3 previous errors

Answer 1

This error appears when you mismatch the version of Substrate you are using across your project.

See previous answers on this forum like: How to resolve duplicate lang item error?

For example, in your project, you see that everything is using branch = "polkadot-v0.9.35", but the tutorial says to copy branch = "polkadot-v0.9.28", so you should make sure when you are copying from the tutorial, to change the branch to match the rest of your project.