Frequent Errors

The main errors happen during development of runtime pallet are followings.

error: duplicate lang item in crate
error: the wasm32-unknown-unknown target is not supported by default, you may need to enable the "js" feature
error[E0603]: module "group" is private
error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
error[E0432]: unresolved import sp_core::to_substrate_wasm_fn_return_value
error: failed to parse manifest at failed to parse the version requirement '0.11 ' for dependency 'parking_lot'
error: could not compile 'node-template' Caused by: process didn't exit successfully:
error[E0432]: unresolved import 'rand_core::OsRng'
error[E0433]: failed to resolve: use of undeclared crate or module imp

Explaining causes and remedies.

error: duplicate lang item in crate

This error happens when we use different version crate but same crate on one crate. The error says the dependencies duplication so we can query the crate name as following.

$ cargo tree -e features -i {crate}

If we find the duplication of crate that we use same crate different version multiple times, we should align the version.

error: the wasm32-unknown-unknown target is not supported by default, you may need to enable the "js" feature

This error happens getrandom crate dependency on std.
We need to disable std feature of getrandom.

Firstly, checking which libraries depend on getrandom depending on std to execute following command.

$ cargo tree -e features

cargo tree command displays the dependencies tree.
The libraries with (*) doesn't depend on std but if there is getrandom not marked as (*), it would cause error.

Secondly, independing from std library by followings.

Add default-features = false to crate in Cargo.toml which is not marked as (*)
Add #![cfg_attr(not(feature = "std"), no_std)] if imported crate is made by self.

And run cargo tree and check whether getrandom is marked as (*)

You can also use cargo nono check to check dependency on std.

$ cargo nono check

error[E0603]: module "group" is private

This error happens syn crate because its interface was change. We need to indicate exact version of syn as using expected behavior.

$ cargo update -p syn --precise 1.0.96

error[E0512]: cannot transmute between types of different sizes, or dependently-sized types

This error happens on runtime-interface and both macro available when #[cfg(all(not(feature = "std"), not(feature = "disable_target_static_assertions")))] so we need to specify std as following.

[features]
default = ["std"]
std = [
    "crate/std"
]

error[E0432]: unresolved import sp_core::to_substrate_wasm_fn_return_value

This error happens the crate which has sp_api dependency. And to clarify every crate which imported as default-features = false is described as crate/std in [features].

[features]
default = ["std"]
std = [
    "crate/std"
]

error: failed to parse manifest at failed to parse the version requirement '0.11 ' for dependency 'parking_lot'

This error happens the crate parity-db fails to find parking_lot version.

$ cargo update -p parity-db

error: could not compile 'node-template' Caused by: process didn't exit successfully:

This error happens because of nightly tool chain version difference. You need to select correct nightly tool chain version with following Polkadot release. https://github.com/paritytech/polkadot/releases

error[E0432]: unresolved import 'rand_core::OsRng'

This error happens because there is no OsRng in rand_core root.

[dev-dependencies]
rand_core = { version="0.6.4", features = ["getrandom"] }

error[E0433]: failed to resolve: use of undeclared crate or module `imp`

This error happens when some crates depend on getrandom. We don't have exact answer for this error.