Use InputString instead of String

Done so that we can correctly support builds without an allocator.

Add two new error types that wrap `InputString`.

units/Cargo.toml

@@ -14,8 +14,8 @@ exclude = ["tests", "contrib"]
 
 [features]
 default = ["std"]
-std = ["alloc"]
+std = ["alloc", "internals/std"]
-alloc = []
+alloc = ["internals/alloc"]
 
 [package.metadata.docs.rs]
 all-features = true

units/src/amount.rs

@@ -12,6 +12,7 @@ use core::{default, ops};
 
 #[cfg(feature = "serde")]
 use ::serde::{Deserialize, Serialize};
+use internals::error::InputString;
 use internals::write_err;
 
 #[cfg(feature = "alloc")]
@@ -129,12 +130,12 @@ impl FromStr for Denomination {
         use self::ParseDenominationError::*;
 
         if CONFUSING_FORMS.contains(&s) {
-            return Err(PossiblyConfusing(s.to_string()));
+            return Err(PossiblyConfusing(PossiblyConfusingDenominationError(s.into())));
         };
 
         let form = self::Denomination::forms(s);
 
-        form.ok_or_else(|| Unknown(s.to_string()))
+        form.ok_or_else(|| Unknown(UnknownDenominationError(s.into())))
     }
 }
 
@@ -196,9 +197,9 @@ impl From<ParseDenominationError> for ParseAmountError {
 #[non_exhaustive]
 pub enum ParseDenominationError {
     /// The denomination was unknown.
-    Unknown(String),
+    Unknown(UnknownDenominationError),
     /// The denomination has multiple possible interpretations.
-    PossiblyConfusing(String),
+    PossiblyConfusing(PossiblyConfusingDenominationError),
 }
 
 impl fmt::Display for ParseDenominationError {
@@ -206,16 +207,8 @@ impl fmt::Display for ParseDenominationError {
         use ParseDenominationError::*;
 
         match *self {
-            Unknown(ref d) => write!(f, "unknown denomination: {}", d),
+            Unknown(ref e) => write_err!(f, "denomination parse error"; e),
-            PossiblyConfusing(ref d) => {
+            PossiblyConfusing(ref e) => write_err!(f, "denomination parse error"; e),
-                let (letter, upper, lower) = match d.chars().next() {
-                    Some('M') => ('M', "Mega", "milli"),
-                    Some('P') => ('P', "Peta", "pico"),
-                    // This panic could be avoided by adding enum ConfusingDenomination { Mega, Peta } but is it worth it?
-                    _ => panic!("invalid error information"),
-                };
-                write!(f, "the '{}' at the beginning of {} should technically mean '{}' but that denomination is uncommon and maybe '{}' was intended", letter, d, upper, lower)
-            }
         }
     }
 }
@@ -231,6 +224,38 @@ impl std::error::Error for ParseDenominationError {
     }
 }
 
+/// Parsing error, unknown denomination.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub struct UnknownDenominationError(InputString);
+
+impl fmt::Display for UnknownDenominationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.0.unknown_variant("bitcoin denomination", f)
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for UnknownDenominationError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { None }
+}
+
+/// Parsing error, possibly confusing denomination.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub struct PossiblyConfusingDenominationError(InputString);
+
+impl fmt::Display for PossiblyConfusingDenominationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}: possibly confusing denomination - we intentionally do not support 'M' and 'P' so as to not confuse mega/milli and peta/pico", self.0.display_cannot_parse("bitcoin denomination"))
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for PossiblyConfusingDenominationError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { None }
+}
+
 fn is_too_precise(s: &str, precision: usize) -> bool {
     match s.find('.') {
         Some(pos) =>
@@ -1994,21 +2019,23 @@ mod tests {
     #[test]
     #[allow(clippy::inconsistent_digit_grouping)] // Group to show 100,000,000 sats per bitcoin.
     fn from_str() {
+        use ParseDenominationError::*;
+
         use super::ParseAmountError as E;
 
         assert_eq!(Amount::from_str("x BTC"), Err(E::InvalidCharacter('x')));
         assert_eq!(
             Amount::from_str("xBTC"),
-            Err(ParseDenominationError::Unknown("xBTC".into()).into())
+            Err(Unknown(UnknownDenominationError("xBTC".into())).into()),
         );
         assert_eq!(
             Amount::from_str("5 BTC BTC"),
-            Err(ParseDenominationError::Unknown("BTC BTC".into()).into())
+            Err(Unknown(UnknownDenominationError("BTC BTC".into())).into()),
         );
         assert_eq!(Amount::from_str("5BTC BTC"), Err(E::InvalidCharacter('B')));
         assert_eq!(
             Amount::from_str("5 5 BTC"),
-            Err(ParseDenominationError::Unknown("5 BTC".into()).into())
+            Err(Unknown(UnknownDenominationError("5 BTC".into())).into()),
         );
 
         #[track_caller]
@@ -2023,7 +2050,7 @@ mod tests {
             assert_eq!(SignedAmount::from_str(&s.replace(' ', "")), expected);
         }
 
-        case("5 BCH", Err(ParseDenominationError::Unknown("BCH".into()).into()));
+        case("5 BCH", Err(Unknown(UnknownDenominationError("BCH".into())).into()));
 
         case("-1 BTC", Err(E::Negative));
         case("-0.0 BTC", Err(E::Negative));
@@ -2133,7 +2160,10 @@ mod tests {
 
     #[test]
     fn to_string_with_denomination_from_str_roundtrip() {
+        use ParseDenominationError::*;
+
         use super::Denomination as D;
+
         let amt = Amount::from_sat(42);
         let denom = Amount::to_string_with_denomination;
         assert_eq!(Amount::from_str(&denom(amt, D::Bitcoin)), Ok(amt));
@@ -2147,11 +2177,11 @@ mod tests {
 
         assert_eq!(
             Amount::from_str("42 satoshi BTC"),
-            Err(ParseDenominationError::Unknown("satoshi BTC".to_owned()).into()),
+            Err(Unknown(UnknownDenominationError("satoshi BTC".into())).into()),
         );
         assert_eq!(
             SignedAmount::from_str("-42 satoshi BTC"),
-            Err(ParseDenominationError::Unknown("satoshi BTC".to_owned()).into()),
+            Err(Unknown(UnknownDenominationError("satoshi BTC".into())).into()),
         );
     }