Merge rust-bitcoin#5105: Fix clippy lints with no-default-features

a4be941 Feature gate unused const (Jamil Lambert, PhD)
5e2eeb8 Fix clippy error: struct is never constructed (Jamil Lambert, PhD)
fdce327 Fix explicit lifetime clippy lints (Jamil Lambert, PhD)
f38221c Fix lint error: passing a unit value to a function (Jamil Lambert, PhD)

Pull request description:

  In preparation for adding crate specific clippy runs in CI with no-default-features, fix all the current lint errors when running it locally in each crate.
  
  There is one clippy error locally in primitives from an unused import (only used with alloc), but it is fixed in rust-bitcoin#4998.


ACKs for top commit:
  apoelstra:
    ACK a4be941; successfully ran local tests
  tcharding:
    ACK a4be941


Tree-SHA512: e5f601213782e7ccceecfbdd022020f830dc321d6e31d522a1b93cf56c15735bccb72f3987d8fc6f633dba7ec8b88369aa65429992d97a3c15883c4622c5fd90

Author: apoelstra

benches/chacha20_poly1305/chacha20poly1305.rs

@@ -46,7 +46,8 @@ fn bench_chacha20poly1305(c: &mut Criterion) {
                 let mut buf = ct.clone();
                 let cipher = ChaCha20Poly1305::new(key, nonce);
                 let res = cipher.decrypt(black_box(&mut buf), tag, Some(aad));
-                black_box(res.unwrap());
+                res.unwrap();
+                black_box(());
             });
         });
     }

bitcoin/src/psbt/mod.rs

@@ -753,7 +753,7 @@ impl<'de> serde::Deserialize<'de> for Psbt {
     {
         struct Visitor;
 
-        impl<'de> serde::de::Visitor<'de> for Visitor {
+        impl serde::de::Visitor<'_> for Visitor {
             type Value = Psbt;
 
             fn expecting(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {

consensus_encoding/src/encode/encoders.rs

@@ -260,7 +260,7 @@ mod tests {
 
     struct TestBytes<'a>(&'a [u8]);
 
-    impl<'a> Encodable for TestBytes<'a> {
+    impl Encodable for TestBytes<'_> {
         type Encoder<'s>
             = BytesEncoder<'s>
         where

consensus_encoding/tests/encode.rs

@@ -8,8 +8,10 @@ use std::io::{Cursor, Write};
 use consensus_encoding::{ArrayEncoder, BytesEncoder, Encodable, Encoder};
 
 // Simple test type that implements Encodable.
+#[cfg(feature = "alloc")]
 struct TestData(u32);
 
+#[cfg(feature = "alloc")]
 impl Encodable for TestData {
     type Encoder<'s>
         = ArrayEncoder<4>
@@ -22,8 +24,10 @@ impl Encodable for TestData {
 }
 
 // Test with a type that creates an empty encoder.
+#[cfg(feature = "alloc")]
 struct EmptyData;
 
+#[cfg(feature = "alloc")]
 impl Encodable for EmptyData {
     type Encoder<'s>
         = ArrayEncoder<0>

hashes/src/sha256/tests.rs

@@ -178,6 +178,7 @@ fn hash_unoptimized() {
 }
 
 // The midstate of an empty hash engine tagged with "TapLeaf".
+#[cfg(feature = "alloc")]
 const TAP_LEAF_MIDSTATE: Midstate = Midstate::new(
     [
         156, 224, 228, 230, 124, 17, 108, 57, 56, 179, 202, 242, 195, 15, 80, 137, 211, 243, 147,

hashes/src/sha256t/mod.rs

@@ -192,7 +192,9 @@ macro_rules! sha256t_tag_constructor {
 
 #[cfg(test)]
 mod tests {
-    use crate::{sha256, sha256t};
+    use crate::sha256t;
+    #[cfg(feature = "alloc")]
+    use crate::sha256;
 
     const TEST_MIDSTATE: [u8; 32] = [
         156, 224, 228, 230, 124, 17, 108, 57, 56, 179, 202, 242, 195, 15, 80, 137, 211, 243, 147,
@@ -211,8 +213,10 @@ mod tests {
         "ed1382037800c9dd938dd8854f1a8863bcdeb6705069b4b56a66ec22519d5829";
 
     #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default, Hash)]
+    #[cfg(feature = "alloc")]
     pub struct TestHashTag;
 
+    #[cfg(feature = "alloc")]
     impl sha256t::Tag for TestHashTag {
         const MIDSTATE: sha256::Midstate = sha256::Midstate::new(TEST_MIDSTATE, 64);
     }

primitives/src/transaction.rs

@@ -431,7 +431,7 @@ impl<'e> WitnessesEncoder<'e> {
 }
 
 #[cfg(feature = "alloc")]
-impl<'e> Encoder for WitnessesEncoder<'e> {
+impl Encoder for WitnessesEncoder<'_> {
     #[inline]
     fn current_chunk(&self) -> Option<&[u8]> {
         // `advance` sets `cur_enc` to `None` once the slice encoder is completely exhausted.
@@ -628,7 +628,7 @@ impl<'de> Deserialize<'de> for OutPoint {
         if deserializer.is_human_readable() {
             struct StringVisitor;
 
-            impl<'de> de::Visitor<'de> for StringVisitor {
+            impl de::Visitor<'_> for StringVisitor {
                 type Value = OutPoint;
 
                 fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {

primitives/src/witness.rs

@@ -279,7 +279,7 @@ impl Encodable for Witness {
     }
 }
 
-impl<'a> Encoder for WitnessEncoder<'a> {
+impl Encoder for WitnessEncoder<'_> {
     #[inline]
     fn current_chunk(&self) -> Option<&[u8]> { self.0.current_chunk() }