primitives: Make hex optional

Make the `hex` dependency optional. This means not implementing
`Display` for some types if `hex` is not enabled and only implementing
`Debug`.

Also without `hex` enabled:

- We loose the ability to parse an `OutPoint` from string because we
  can no longer parse `Txid`.

- We loose the hex formatting of witness elements.

Note also that `primitives` builds with the `serde` feature even if
`hex?/serde` is excluded from the `serde` feature. I found this
surprising.

Cargo-minimal.lock

@@ -213,6 +213,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4afe881d0527571892c4034822e59bb10c6c991cce6abe8199b6f5cf10766f55"
 dependencies = [
  "arrayvec",
+ "serde",
 ]
 
 [[package]]

Cargo-recent.lock

@@ -215,6 +215,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4afe881d0527571892c4034822e59bb10c6c991cce6abe8199b6f5cf10766f55"
 dependencies = [
  "arrayvec",
+ "serde",
 ]
 
 [[package]]

bitcoin/Cargo.toml

@@ -31,7 +31,7 @@ hashes = { package = "bitcoin_hashes", path = "../hashes", default-features = fa
 hex = { package = "hex-conservative", version = "0.3.0", default-features = false, features = ["alloc"] }
 internals = { package = "bitcoin-internals", path = "../internals", features = ["alloc", "hex"] }
 io = { package = "bitcoin-io", path = "../io", default-features = false, features = ["alloc", "hashes"] }
-primitives = { package = "bitcoin-primitives", path = "../primitives", default-features = false, features = ["alloc"] }
+primitives = { package = "bitcoin-primitives", path = "../primitives", default-features = false, features = ["alloc", "hex"] }
 secp256k1 = { version = "0.30.0", default-features = false, features = ["hashes", "alloc", "rand"] }
 units = { package = "bitcoin-units", path = "../units", default-features = false, features = ["alloc"] }
 

primitives/Cargo.toml

@@ -15,19 +15,20 @@ rust-version = "1.63.0"
 exclude = ["tests", "contrib"]
 
 [features]
-default = ["std"]
-std = ["alloc", "hashes/std", "hex/std", "internals/std", "units/std"]
-alloc = ["hashes/alloc", "hex/alloc", "internals/alloc", "units/alloc"]
-serde = ["dep:serde", "hashes/serde", "internals/serde", "units/serde", "alloc"]
+default = ["std", "hex"]
+std = ["alloc", "hashes/std", "hex?/std", "internals/std", "units/std"]
+alloc = ["hashes/alloc", "hex?/alloc", "internals/alloc", "units/alloc"]
+serde = ["dep:serde", "hashes/serde", "hex?/serde", "internals/serde", "units/serde", "alloc", "hex"]
 arbitrary = ["dep:arbitrary", "units/arbitrary"]
+hex = ["dep:hex", "hashes/hex", "internals/hex"]
 
 [dependencies]
-hashes = { package = "bitcoin_hashes", path = "../hashes", default-features = false, features = ["hex"] }
-hex = { package = "hex-conservative", version = "0.3.0", default-features = false }
-internals = { package = "bitcoin-internals", path = "../internals", features = ["hex"] }
+hashes = { package = "bitcoin_hashes", path = "../hashes", default-features = false }
+internals = { package = "bitcoin-internals", path = "../internals" }
 units = { package = "bitcoin-units", path = "../units", default-features = false }
 
 arbitrary = { version = "1.4", optional = true }
+hex = { package = "hex-conservative", version = "0.3.0", default-features = false, optional = true }
 serde = { version = "1.0.103", default-features = false, features = ["derive", "alloc"], optional = true }
 
 [dev-dependencies]

primitives/src/block.rs

@@ -310,7 +310,10 @@ hashes::hash_newtype! {
     pub struct WitnessCommitment(sha256d::Hash);
 }
 
+#[cfg(feature = "hex")]
 hashes::impl_hex_for_newtype!(BlockHash, WitnessCommitment);
+#[cfg(not(feature = "hex"))]
+hashes::impl_debug_only_for_newtype!(BlockHash, WitnessCommitment);
 #[cfg(feature = "serde")]
 hashes::impl_serde_for_newtype!(BlockHash, WitnessCommitment);
 

primitives/src/merkle_tree.rs

@@ -11,6 +11,9 @@ hashes::hash_newtype! {
     pub struct WitnessMerkleNode(sha256d::Hash);
 }
 
+#[cfg(feature = "hex")]
 hashes::impl_hex_for_newtype!(TxMerkleNode, WitnessMerkleNode);
+#[cfg(not(feature = "hex"))]
+hashes::impl_debug_only_for_newtype!(TxMerkleNode, WitnessMerkleNode);
 #[cfg(feature = "serde")]
 hashes::impl_serde_for_newtype!(TxMerkleNode, WitnessMerkleNode);

primitives/src/script/mod.rs

@@ -10,6 +10,7 @@ use core::convert::Infallible;
 use core::fmt;
 
 use hashes::{hash160, sha256};
+#[cfg(feature = "hex")]
 use hex::DisplayHex;
 use internals::script::{self, PushDataLenLen};
 
@@ -49,7 +50,10 @@ hashes::hash_newtype! {
     pub struct WScriptHash(sha256::Hash);
 }
 
+#[cfg(feature = "hex")]
 hashes::impl_hex_for_newtype!(ScriptHash, WScriptHash);
+#[cfg(not(feature = "hex"))]
+hashes::impl_debug_only_for_newtype!(ScriptHash, WScriptHash);
 #[cfg(feature = "serde")]
 hashes::impl_serde_for_newtype!(ScriptHash, WScriptHash);
 
@@ -425,6 +429,7 @@ impl fmt::Display for ScriptBuf {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Display::fmt(self.as_script(), f) }
 }
 
+#[cfg(feature = "hex")]
 impl fmt::LowerHex for Script {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -432,15 +437,19 @@ impl fmt::LowerHex for Script {
     }
 }
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 internals::impl_to_hex_from_lower_hex!(Script, |script: &Self| script.len() * 2);
 
+#[cfg(feature = "hex")]
 impl fmt::LowerHex for ScriptBuf {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::LowerHex::fmt(self.as_script(), f) }
 }
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 internals::impl_to_hex_from_lower_hex!(ScriptBuf, |script_buf: &Self| script_buf.len() * 2);
 
+#[cfg(feature = "hex")]
 impl fmt::UpperHex for Script {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -448,6 +457,7 @@ impl fmt::UpperHex for Script {
     }
 }
 
+#[cfg(feature = "hex")]
 impl fmt::UpperHex for ScriptBuf {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::UpperHex::fmt(self.as_script(), f) }
@@ -720,16 +730,24 @@ mod tests {
     fn script_display() {
         let script = Script::from_bytes(&[0xa1, 0xb2, 0xc3]);
         assert_eq!(format!("{}", script), "OP_LESSTHANOREQUAL OP_CSV OP_RETURN_195");
-        assert_eq!(format!("{:x}", script), "a1b2c3");
-        assert_eq!(format!("{:X}", script), "A1B2C3");
+
+        #[cfg(feature = "hex")]
+        {
+            assert_eq!(format!("{:x}", script), "a1b2c3");
+            assert_eq!(format!("{:X}", script), "A1B2C3");
+        }
     }
 
     #[test]
     fn scriptbuf_display() {
         let script_buf = ScriptBuf::from(vec![0xa1, 0xb2, 0xc3]);
         assert_eq!(format!("{}", script_buf), "OP_LESSTHANOREQUAL OP_CSV OP_RETURN_195");
-        assert_eq!(format!("{:x}", script_buf), "a1b2c3");
-        assert_eq!(format!("{:X}", script_buf), "A1B2C3");
+
+        #[cfg(feature = "hex")]
+        {
+            assert_eq!(format!("{:x}", script_buf), "a1b2c3");
+            assert_eq!(format!("{:X}", script_buf), "A1B2C3");
+        }
     }
 
     #[test]

primitives/src/transaction.rs

@@ -13,6 +13,7 @@
 #[cfg(feature = "alloc")]
 use core::cmp;
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 use core::convert::Infallible;
 use core::fmt;
 
@@ -20,9 +21,13 @@ use core::fmt;
 use arbitrary::{Arbitrary, Unstructured};
 use hashes::sha256d;
 #[cfg(feature = "alloc")]
-use internals::{compact_size, write_err};
+use internals::compact_size;
+#[cfg(feature = "hex")]
+use internals::write_err;
+#[cfg(feature = "hex")]
+use units::parse;
 #[cfg(feature = "alloc")]
-use units::{parse, Amount, Weight};
+use units::{Amount, Weight};
 
 #[cfg(feature = "alloc")]
 use crate::locktime::absolute;
@@ -389,6 +394,7 @@ impl OutPoint {
     pub const COINBASE_PREVOUT: Self = Self { txid: Txid::COINBASE_PREVOUT, vout: u32::MAX };
 }
 
+#[cfg(feature = "hex")]
 impl fmt::Display for OutPoint {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -397,6 +403,7 @@ impl fmt::Display for OutPoint {
 }
 
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 impl core::str::FromStr for OutPoint {
     type Err = ParseOutPointError;
 
@@ -424,6 +431,7 @@ impl core::str::FromStr for OutPoint {
 ///
 /// Does not permit leading zeroes or non-digit characters.
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 fn parse_vout(s: &str) -> Result<u32, ParseOutPointError> {
     if s.len() > 1 {
         let first = s.chars().next().unwrap();
@@ -438,6 +446,7 @@ fn parse_vout(s: &str) -> Result<u32, ParseOutPointError> {
 #[derive(Debug, Clone, PartialEq, Eq)]
 #[non_exhaustive]
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 pub enum ParseOutPointError {
     /// Error in TXID part.
     Txid(hex::HexToArrayError),
@@ -452,12 +461,14 @@ pub enum ParseOutPointError {
 }
 
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 impl From<Infallible> for ParseOutPointError {
     #[inline]
     fn from(never: Infallible) -> Self { match never {} }
 }
 
 #[cfg(feature = "alloc")]
+#[cfg(feature = "hex")]
 impl fmt::Display for ParseOutPointError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use ParseOutPointError as E;
@@ -473,6 +484,7 @@ impl fmt::Display for ParseOutPointError {
 }
 
 #[cfg(feature = "std")]
+#[cfg(feature = "hex")]
 impl std::error::Error for ParseOutPointError {
     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
         use ParseOutPointError as E;
@@ -500,7 +512,10 @@ hashes::hash_newtype! {
     pub struct Wtxid(sha256d::Hash);
 }
 
+#[cfg(feature = "hex")]
 hashes::impl_hex_for_newtype!(Txid, Wtxid);
+#[cfg(not(feature = "hex"))]
+hashes::impl_debug_only_for_newtype!(Txid, Wtxid);
 #[cfg(feature = "serde")]
 hashes::impl_serde_for_newtype!(Txid, Wtxid);
 
@@ -699,6 +714,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "hex")]
     fn outpoint_from_str() {
         // Check format errors
         let mut outpoint_str = "0".repeat(64); // No ":"
@@ -725,6 +741,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "hex")]
     fn canonical_vout() {
         assert_eq!(parse_vout("0").unwrap(), 0);
         assert_eq!(parse_vout("1").unwrap(), 1);

primitives/src/witness.rs

@@ -9,7 +9,6 @@ use core::ops::Index;
 
 #[cfg(feature = "arbitrary")]
 use arbitrary::{Arbitrary, Unstructured};
-use hex::DisplayHex;
 use internals::compact_size;
 use internals::slice::SliceExt;
 use internals::wrap_debug::WrapDebug;
@@ -314,7 +313,7 @@ impl<T: core::borrow::Borrow<[u8]>> PartialEq<Witness> for alloc::sync::Arc<[T]>
 /// Debug implementation that displays the witness as a structured output containing:
 /// - Number of witness elements
 /// - Total bytes across all elements
-/// - List of hex-encoded witness elements
+/// - List of hex-encoded witness elements if `hex` features is enabled.
 #[allow(clippy::missing_fields_in_debug)] // We don't want to show `indices_start`.
 impl fmt::Debug for Witness {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -326,7 +325,14 @@ impl fmt::Debug for Witness {
             .field(
                 "elements",
                 &WrapDebug(|f| {
-                    f.debug_list().entries(self.iter().map(DisplayHex::as_hex)).finish()
+                    #[cfg(feature = "hex")]
+                    {
+                        f.debug_list().entries(self.iter().map(hex::DisplayHex::as_hex)).finish()
+                    }
+                    #[cfg(not(feature = "hex"))]
+                    {
+                        f.debug_list().entries(self.iter()).finish()
+                    }
                 }),
             )
             .finish()