[ci] Add `-D warnings` for `cargo-check-each-crate` job to fail on warnings (#2670)

## Summary

This PR turns on `-D warnings` for `cargo-check-each-crate job` job to
fail on warnings e.g. like this:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673130

Before this PR, there was a warning and `cargo-check-each-crate` job did
not fail:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4641444
```
warning: unused import: `ToTokens`
  --> substrate/primitives/api/proc-macro/src/utils.rs:22:34
   |
22 | use quote::{format_ident, quote, ToTokens};
   |                                  ^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default
warning: `sp-api-proc-macro` (lib) generated 1 warning (run `cargo fix --lib -p sp-api-proc-macro` to apply 1 suggestion)
```

Fixes on the way:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4641444
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673265
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673410
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673681
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673836
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4673941
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4674256
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4679328



## Questions
- [ ] why does this check triggers only `cargo check --locked`?
`--all-features` or `--all-targets` are not needed? Or aren't they
avoided intentionally?

---------

Co-authored-by: command-bot <>

.gitlab/pipeline/test.yml

@@ -438,6 +438,7 @@ cargo-check-each-crate:
     - .run-immediately
     # - .collect-artifacts
   variables:
+    RUSTFLAGS: "-D warnings"
     # $CI_JOB_NAME is set manually so that cache could be shared for all jobs
     # "cargo-check-each-crate I/N" jobs
     CI_JOB_NAME: cargo-check-each-crate

substrate/client/network/src/behaviour.rs

@@ -39,7 +39,7 @@ use parking_lot::Mutex;
 use sp_runtime::traits::Block as BlockT;
 use std::{collections::HashSet, sync::Arc, time::Duration};
 
-pub use crate::request_responses::{InboundFailure, OutboundFailure, RequestId, ResponseFailure};
+pub use crate::request_responses::{InboundFailure, OutboundFailure, ResponseFailure};
 
 /// General behaviour of the network. Combines all protocols together.
 #[derive(NetworkBehaviour)]

substrate/client/network/src/protocol/message.rs

@@ -19,10 +19,6 @@
 //! Network packet message types. These get serialized and put into the lower level protocol
 //! payload.
 
-pub use self::generic::{
-	RemoteCallRequest, RemoteChangesRequest, RemoteChangesResponse, RemoteHeaderRequest,
-	RemoteHeaderResponse, RemoteReadChildRequest, RemoteReadRequest,
-};
 use codec::{Decode, Encode};
 use sc_client_api::StorageProof;
 use sc_network_common::message::RequestId;

substrate/client/network/src/protocol/notifications/upgrade.rs

@@ -16,12 +16,14 @@
 // You should have received a copy of the GNU General Public License
 // along with this program. If not, see <https://www.gnu.org/licenses/>.
 
+#[cfg(test)]
+pub(crate) use self::notifications::{
+	NotificationsInOpen, NotificationsInSubstreamHandshake, NotificationsOutOpen,
+};
 pub use self::{
 	collec::UpgradeCollec,
 	notifications::{
-		NotificationsHandshakeError, NotificationsIn, NotificationsInOpen,
-		NotificationsInSubstream, NotificationsInSubstreamHandshake, NotificationsOut,
-		NotificationsOutError, NotificationsOutOpen, NotificationsOutSubstream,
+		NotificationsIn, NotificationsInSubstream, NotificationsOut, NotificationsOutSubstream,
 	},
 };
 

substrate/client/offchain/src/api.rs

@@ -30,7 +30,6 @@ use sp_core::{
 	},
 	OpaquePeerId,
 };
-pub use sp_offchain::STORAGE_PREFIX;
 
 mod http;
 

substrate/client/transaction-pool/src/graph/mod.rs

@@ -39,9 +39,6 @@ pub mod watcher;
 
 pub use self::{
 	base_pool::Transaction,
-	pool::{
-		BlockHash, ChainApi, EventStream, ExtrinsicFor, ExtrinsicHash, NumberFor, Options, Pool,
-		TransactionFor,
-	},
+	pool::{BlockHash, ChainApi, ExtrinsicFor, ExtrinsicHash, NumberFor, Options, Pool},
 };
 pub use validated_pool::{IsValidator, ValidatedTransaction};

substrate/frame/contracts/proc-macro/src/lib.rs

@@ -74,7 +74,7 @@ fn derive_debug(input: TokenStream, fmt: impl Fn(&Ident) -> TokenStream2) -> Tok
 	#[cfg(not(feature = "full"))]
 	let fields = {
 		drop(fmt);
-		drop(data);
+		let _ = data;
 		TokenStream2::new()
 	};
 

substrate/primitives/api/proc-macro/src/utils.rs

@@ -19,7 +19,7 @@ use crate::common::API_VERSION_ATTRIBUTE;
 use inflector::Inflector;
 use proc_macro2::{Span, TokenStream};
 use proc_macro_crate::{crate_name, FoundCrate};
-use quote::{format_ident, quote, ToTokens};
+use quote::{format_ident, quote};
 use syn::{
 	parse_quote, spanned::Spanned, token::And, Attribute, Error, FnArg, GenericArgument, Ident,
 	ImplItem, ItemImpl, Pat, Path, PathArguments, Result, ReturnType, Signature, Type, TypePath,
@@ -261,6 +261,7 @@ pub fn versioned_trait_name(trait_ident: &Ident, version: u64) -> Ident {
 /// Extract the documentation from the provided attributes.
 #[cfg(feature = "frame-metadata")]
 pub fn get_doc_literals(attrs: &[syn::Attribute]) -> Vec<syn::Lit> {
+	use quote::ToTokens;
 	attrs
 		.iter()
 		.filter_map(|attr| {

substrate/primitives/state-machine/src/lib.rs

@@ -142,7 +142,6 @@ pub use crate::{
 mod std_reexport {
 	pub use crate::{
 		basic::BasicExternalities,
-		error::{Error, ExecutionError},
 		in_memory_backend::new_in_mem,
 		read_only::{InspectState, ReadOnlyExternalities},
 		testing::TestExternalities,