chore: deprecate void crate (libp2p#5676)

## Description

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The `void` crate provides a `Void` type that is conceptually equivalent
to the [`never`
type(!)](https://doc.rust-lang.org/std/primitive.never.html). This PR
tries to remove `void` crate from the dependency tree by replacing
`void::Void` with
[`std::convert::Infallible`](https://doc.rust-lang.org/std/convert/enum.Infallible.html)
that will eventually become an alias of the `never` type(!)

> This enum has the same role as [the ! “never”
type](https://doc.rust-lang.org/std/primitive.never.html), which is
unstable in this version of Rust. When ! is stabilized, we plan to make
Infallible a type alias to it:

## Notes & open questions

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## Change checklist

<!-- Please add a Changelog entry in the appropriate crates and bump the
crate versions if needed. See
<https://github.com/libp2p/rust-libp2p/blob/master/docs/release.md#development-between-releases>-->

- [x] I have performed a self-review of my own code
- [ ] I have made corresponding changes to the documentation
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] A changelog entry has been made in the appropriate crates

core/Cargo.toml

@@ -31,7 +31,6 @@ smallvec = "1.13.2"
 thiserror = "1.0"
 tracing = { workspace = true }
 unsigned-varint = { workspace = true }
-void = "1"
 
 [dev-dependencies]
 async-std = { version = "1.6.2", features = ["attributes"] }

core/src/lib.rs

@@ -66,3 +66,13 @@ pub use upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
 #[derive(Debug, thiserror::Error)]
 #[error(transparent)]
 pub struct DecodeError(quick_protobuf::Error);
+
+pub mod util {
+    use std::convert::Infallible;
+
+    /// A safe version of [`std::intrinsics::unreachable`].
+    #[inline(always)]
+    pub fn unreachable(x: Infallible) -> ! {
+        match x {}
+    }
+}

core/src/upgrade/denied.rs

@@ -20,8 +20,8 @@
 
 use crate::upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
 use futures::future;
+use std::convert::Infallible;
 use std::iter;
-use void::Void;
 
 /// Dummy implementation of `UpgradeInfo`/`InboundUpgrade`/`OutboundUpgrade` that doesn't support
 /// any protocol.
@@ -38,8 +38,8 @@ impl UpgradeInfo for DeniedUpgrade {
 }
 
 impl<C> InboundUpgrade<C> for DeniedUpgrade {
-    type Output = Void;
-    type Error = Void;
+    type Output = Infallible;
+    type Error = Infallible;
     type Future = future::Pending<Result<Self::Output, Self::Error>>;
 
     fn upgrade_inbound(self, _: C, _: Self::Info) -> Self::Future {
@@ -48,8 +48,8 @@ impl<C> InboundUpgrade<C> for DeniedUpgrade {
 }
 
 impl<C> OutboundUpgrade<C> for DeniedUpgrade {
-    type Output = Void;
-    type Error = Void;
+    type Output = Infallible;
+    type Error = Infallible;
     type Future = future::Pending<Result<Self::Output, Self::Error>>;
 
     fn upgrade_outbound(self, _: C, _: Self::Info) -> Self::Future {

core/src/upgrade/pending.rs

@@ -21,8 +21,8 @@
 
 use crate::upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
 use futures::future;
+use std::convert::Infallible;
 use std::iter;
-use void::Void;
 
 /// Implementation of [`UpgradeInfo`], [`InboundUpgrade`] and [`OutboundUpgrade`] that always
 /// returns a pending upgrade.
@@ -53,8 +53,8 @@ impl<C, P> InboundUpgrade<C> for PendingUpgrade<P>
 where
     P: AsRef<str> + Clone,
 {
-    type Output = Void;
-    type Error = Void;
+    type Output = Infallible;
+    type Error = Infallible;
     type Future = future::Pending<Result<Self::Output, Self::Error>>;
 
     fn upgrade_inbound(self, _: C, _: Self::Info) -> Self::Future {
@@ -66,8 +66,8 @@ impl<C, P> OutboundUpgrade<C> for PendingUpgrade<P>
 where
     P: AsRef<str> + Clone,
 {
-    type Output = Void;
-    type Error = Void;
+    type Output = Infallible;
+    type Error = Infallible;
     type Future = future::Pending<Result<Self::Output, Self::Error>>;
 
     fn upgrade_outbound(self, _: C, _: Self::Info) -> Self::Future {

core/src/upgrade/ready.rs

@@ -21,8 +21,8 @@
 
 use crate::upgrade::{InboundUpgrade, OutboundUpgrade, UpgradeInfo};
 use futures::future;
+use std::convert::Infallible;
 use std::iter;
-use void::Void;
 
 /// Implementation of [`UpgradeInfo`], [`InboundUpgrade`] and [`OutboundUpgrade`] that directly yields the substream.
 #[derive(Debug, Copy, Clone)]
@@ -53,7 +53,7 @@ where
     P: AsRef<str> + Clone,
 {
     type Output = C;
-    type Error = Void;
+    type Error = Infallible;
     type Future = future::Ready<Result<Self::Output, Self::Error>>;
 
     fn upgrade_inbound(self, stream: C, _: Self::Info) -> Self::Future {
@@ -66,7 +66,7 @@ where
     P: AsRef<str> + Clone,
 {
     type Output = C;
-    type Error = Void;
+    type Error = Infallible;
     type Future = future::Ready<Result<Self::Output, Self::Error>>;
 
     fn upgrade_outbound(self, stream: C, _: Self::Info) -> Self::Future {

examples/file-sharing/Cargo.toml

@@ -16,7 +16,6 @@ futures = { workspace = true }
 libp2p = { path = "../../libp2p", features = [ "tokio", "cbor", "dns", "kad", "noise", "macros", "request-response", "tcp", "websocket", "yamux"] }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true, features = ["env-filter"] }
-void = "1.0.2"
 
 [lints]
 workspace = true

identity/Cargo.toml

@@ -26,15 +26,14 @@ sec1 = { version = "0.7", default-features = false, optional = true }
 serde = { version = "1", optional = true, features = ["derive"] }
 sha2 = { version = "0.10.8", optional = true }
 thiserror = { version = "1.0", optional = true }
-void = { version = "1.0", optional = true }
 zeroize = { version = "1.8", optional = true }
 
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 ring = { workspace = true, features = ["alloc", "std"], optional = true }
 
 [features]
 secp256k1 = ["dep:libsecp256k1", "dep:asn1_der", "dep:sha2", "dep:hkdf", "dep:zeroize"]
-ecdsa = ["dep:p256", "dep:void", "dep:zeroize", "dep:sec1", "dep:sha2", "dep:hkdf"]
+ecdsa = ["dep:p256", "dep:zeroize", "dep:sec1", "dep:sha2", "dep:hkdf"]
 rsa = ["dep:ring", "dep:asn1_der", "dep:rand", "dep:zeroize"]
 ed25519 = ["dep:ed25519-dalek", "dep:zeroize", "dep:sha2", "dep:hkdf"]
 peerid = ["dep:multihash", "dep:bs58", "dep:thiserror", "dep:sha2", "dep:hkdf"]

identity/src/ecdsa.rs

@@ -32,7 +32,7 @@ use p256::{
     EncodedPoint,
 };
 use sec1::{DecodeEcPrivateKey, EncodeEcPrivateKey};
-use void::Void;
+use std::convert::Infallible;
 use zeroize::Zeroize;
 
 /// An ECDSA keypair generated using `secp256r1` curve.
@@ -182,7 +182,10 @@ impl PublicKey {
     /// Try to decode a public key from a DER encoded byte buffer as defined by SEC1 standard.
     pub fn try_decode_der(k: &[u8]) -> Result<PublicKey, DecodingError> {
         let buf = Self::del_asn1_header(k).ok_or_else(|| {
-            DecodingError::failed_to_parse::<Void, _>("ASN.1-encoded ecdsa p256 public key", None)
+            DecodingError::failed_to_parse::<Infallible, _>(
+                "ASN.1-encoded ecdsa p256 public key",
+                None,
+            )
         })?;
         Self::try_from_bytes(buf)
     }

misc/allow-block-list/Cargo.toml

@@ -13,7 +13,6 @@ categories = ["network-programming", "asynchronous"]
 libp2p-core = { workspace = true }
 libp2p-swarm = { workspace = true }
 libp2p-identity = { workspace = true, features = ["peerid"] }
-void = "1"
 
 [dev-dependencies]
 async-std = { version = "1.12.0", features = ["attributes"] }

misc/allow-block-list/src/lib.rs

@@ -69,9 +69,9 @@ use libp2p_swarm::{
     THandlerInEvent, THandlerOutEvent, ToSwarm,
 };
 use std::collections::{HashSet, VecDeque};
+use std::convert::Infallible;
 use std::fmt;
 use std::task::{Context, Poll, Waker};
-use void::Void;
 
 /// A [`NetworkBehaviour`] that can act as an allow or block list.
 #[derive(Default, Debug)]
@@ -222,7 +222,7 @@ where
     S: Enforce,
 {
     type ConnectionHandler = dummy::ConnectionHandler;
-    type ToSwarm = Void;
+    type ToSwarm = Infallible;
 
     fn handle_established_inbound_connection(
         &mut self,
@@ -273,7 +273,7 @@ where
     ) {
         // TODO: remove when Rust 1.82 is MSRV
         #[allow(unreachable_patterns)]
-        void::unreachable(event)
+        libp2p_core::util::unreachable(event)
     }
 
     fn poll(

misc/connection-limits/Cargo.toml

@@ -13,7 +13,6 @@ categories = ["network-programming", "asynchronous"]
 libp2p-core = { workspace = true }
 libp2p-swarm = { workspace = true }
 libp2p-identity = { workspace = true, features = ["peerid"] }
-void = "1"
 
 [dev-dependencies]
 async-std = { version = "1.12.0", features = ["attributes"] }