Remove usage of impl_from_infallible in crates

Rust macros, while at times useful, are a maintenance nightmare. And
we have been bitten by calling macros from other crates multiple times
in the past.

In a push to just use less macros remove the usage of the
`impl_from_infallible` macro in the bitcoin, units, and internals crates
and just write the code.

base58/src/error.rs

@@ -3,6 +3,7 @@
 //! Error code for the `base58` crate.
 
 use core::fmt;
+use core::convert::Infallible;
 
 use internals::write_err;
 
@@ -20,8 +21,13 @@ pub(super) enum ErrorInner {
     TooShort(TooShortError),
 }
 
-internals::impl_from_infallible!(Error);
-internals::impl_from_infallible!(ErrorInner);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
+
+impl From<Infallible> for ErrorInner {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl Error {
     /// Returns the invalid base58 ssscharacter, if encountered.
@@ -95,7 +101,9 @@ pub(super) struct IncorrectChecksumError {
     pub(super) expected: u32,
 }
 
-internals::impl_from_infallible!(IncorrectChecksumError);
+impl From<Infallible> for IncorrectChecksumError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for IncorrectChecksumError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -116,8 +124,9 @@ pub(super) struct TooShortError {
     /// The length of the decoded data.
     pub(super) length: usize,
 }
-
-internals::impl_from_infallible!(TooShortError);
+impl From<Infallible> for TooShortError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for TooShortError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -141,8 +150,13 @@ pub(super) struct InvalidCharacterErrorInner {
     pub(super) invalid: u8,
 }
 
-internals::impl_from_infallible!(InvalidCharacterError);
-internals::impl_from_infallible!(InvalidCharacterErrorInner);
+impl From<Infallible> for InvalidCharacterError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
+
+impl From<Infallible> for InvalidCharacterErrorInner {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl InvalidCharacterError {
     pub(super) fn new(invalid: u8) -> Self { Self(InvalidCharacterErrorInner { invalid }) }

bitcoin/src/address/error.rs

@@ -1,6 +1,7 @@
 //! Error code for the address module.
 
 use core::fmt;
+use core::convert::Infallible;
 
 use internals::write_err;
 
@@ -21,7 +22,9 @@ pub enum FromScriptError {
     WitnessVersion(witness_version::TryFromError),
 }
 
-internals::impl_from_infallible!(FromScriptError);
+impl From<Infallible> for FromScriptError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for FromScriptError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -84,7 +87,9 @@ pub enum ParseError {
     NetworkValidation(NetworkValidationError),
 }
 
-internals::impl_from_infallible!(ParseError);
+impl From<Infallible> for ParseError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for ParseError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -175,7 +180,9 @@ pub enum Bech32Error {
     UnknownHrp(UnknownHrpError),
 }
 
-internals::impl_from_infallible!(Bech32Error);
+impl From<Infallible> for Bech32Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Bech32Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -221,7 +228,9 @@ impl From<UnknownHrpError> for Bech32Error {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ParseBech32Error(pub(crate) bech32::segwit::DecodeError);
 
-internals::impl_from_infallible!(ParseBech32Error);
+impl From<Infallible> for ParseBech32Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for ParseBech32Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -248,7 +257,9 @@ pub enum Base58Error {
     InvalidLegacyPrefix(InvalidLegacyPrefixError),
 }
 
-internals::impl_from_infallible!(Base58Error);
+impl From<Infallible> for Base58Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Base58Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/bip152.rs

@@ -5,6 +5,7 @@
 //! Implementation of compact blocks data structure and algorithms.
 
 use core::{convert, fmt, mem};
+use core::convert::Infallible;
 #[cfg(feature = "std")]
 use std::error;
 
@@ -30,7 +31,9 @@ pub enum Error {
     InvalidPrefill,
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/bip158.rs

@@ -39,6 +39,7 @@
 
 use core::cmp::{self, Ordering};
 use core::fmt;
+use core::convert::Infallible;
 
 use hashes::{sha256d, siphash24, HashEngine as _};
 use internals::{write_err, ToU64 as _};
@@ -79,7 +80,9 @@ pub enum Error {
     Io(io::Error),
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {

bitcoin/src/bip32.rs

@@ -8,6 +8,7 @@
 use core::ops::Index;
 use core::str::FromStr;
 use core::{fmt, slice};
+use core::convert::Infallible;
 
 use hashes::{hash160, hash_newtype, sha512, GeneralHash, HashEngine, Hmac, HmacEngine};
 use internals::write_err;
@@ -519,7 +520,9 @@ pub enum Error {
     InvalidBase58PayloadLength(InvalidBase58PayloadLengthError),
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/blockdata/block.rs

@@ -8,6 +8,7 @@
 //! these blocks and the blockchain.
 
 use core::fmt;
+use core::convert::Infallible;
 
 use hashes::{sha256d, HashEngine};
 use internals::{compact_size, ToU64};
@@ -383,7 +384,9 @@ pub enum InvalidBlockError {
     InvalidWitnessCommitment,
 }
 
-internals::impl_from_infallible!(InvalidBlockError);
+impl From<Infallible> for InvalidBlockError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for InvalidBlockError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -413,7 +416,9 @@ pub enum Bip34Error {
     NegativeHeight,
 }
 
-internals::impl_from_infallible!(Bip34Error);
+impl From<Infallible> for Bip34Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Bip34Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -457,7 +462,9 @@ pub enum ValidationError {
     BadTarget,
 }
 
-internals::impl_from_infallible!(ValidationError);
+impl From<Infallible> for ValidationError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for ValidationError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/blockdata/script/mod.rs

@@ -58,6 +58,7 @@ pub mod witness_program;
 pub mod witness_version;
 
 use core::fmt;
+use core::convert::Infallible;
 
 use io::{BufRead, Write};
 use primitives::opcodes::all::*;
@@ -234,7 +235,9 @@ pub enum Error {
     Serialization,
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/blockdata/script/witness_program.rs

@@ -8,6 +8,7 @@
 //! [BIP141]: <https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki>
 
 use core::fmt;
+use core::convert::Infallible;
 
 use internals::array_vec::ArrayVec;
 use secp256k1::{Secp256k1, Verification};
@@ -139,7 +140,9 @@ pub enum Error {
     InvalidSegwitV0Length(usize),
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/blockdata/script/witness_version.rs

@@ -9,6 +9,7 @@
 
 use core::fmt;
 use core::str::FromStr;
+use core::convert::Infallible;
 
 use internals::write_err;
 use units::parse::{self, ParseIntError};
@@ -159,7 +160,9 @@ pub enum FromStrError {
     Invalid(TryFromError),
 }
 
-internals::impl_from_infallible!(FromStrError);
+impl From<Infallible> for FromStrError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for FromStrError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -202,7 +205,9 @@ pub enum TryFromInstructionError {
     DataPush,
 }
 
-internals::impl_from_infallible!(TryFromInstructionError);
+impl From<Infallible> for TryFromInstructionError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for TryFromInstructionError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/consensus/error.rs

@@ -3,6 +3,7 @@
 //! Consensus encoding errors.
 
 use core::fmt;
+use core::convert::Infallible;
 
 use hex::error::{InvalidCharError, OddLengthStringError};
 use hex::DisplayHex as _;
@@ -21,7 +22,9 @@ pub enum DeserializeError {
     Unconsumed,
 }
 
-internals::impl_from_infallible!(DeserializeError);
+impl From<Infallible> for DeserializeError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for DeserializeError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -64,7 +67,9 @@ pub enum DecodeError<E> {
     Other(E), // Yielded by the inner iterator.
 }
 
-internals::impl_from_infallible!(DecodeError<E>);
+impl<E> From<Infallible> for DecodeError<E> {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl<E: fmt::Debug> fmt::Display for DecodeError<E> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -101,7 +106,9 @@ pub enum Error {
     Parse(ParseError),
 }
 
-internals::impl_from_infallible!(Error);
+impl From<Infallible> for Error {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -169,7 +176,9 @@ pub enum ParseError {
     UnsupportedSegwitFlag(u8),
 }
 
-internals::impl_from_infallible!(ParseError);
+impl From<Infallible> for ParseError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for ParseError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/consensus_validation.rs

@@ -5,6 +5,7 @@
 //! Relies on the `bitcoinconsensus` crate that uses Bitcoin Core libconsensus to perform validation.
 
 use core::fmt;
+use core::convert::Infallible;
 
 use internals::write_err;
 
@@ -237,7 +238,9 @@ pub enum TxVerifyError {
     UnknownSpentOutput(OutPoint),
 }
 
-internals::impl_from_infallible!(TxVerifyError);
+impl From<Infallible> for TxVerifyError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for TxVerifyError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

bitcoin/src/crypto/ecdsa.rs

@@ -6,6 +6,7 @@
 
 use core::str::FromStr;
 use core::{fmt, iter};
+use core::convert::Infallible;
 
 #[cfg(feature = "arbitrary")]
 use arbitrary::{Arbitrary, Unstructured};
@@ -213,7 +214,9 @@ pub enum DecodeError {
     Secp256k1(secp256k1::Error),
 }
 
-internals::impl_from_infallible!(DecodeError);
+impl From<Infallible> for DecodeError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for DecodeError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -258,7 +261,9 @@ pub enum ParseSignatureError {
     Decode(DecodeError),
 }
 
-internals::impl_from_infallible!(ParseSignatureError);
+impl From<Infallible> for ParseSignatureError {
+    fn from(never: Infallible) -> Self { match never {} }
+}
 
 impl fmt::Display for ParseSignatureError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {