Try using thiserror to remove some boilerplate.

src/errors.rs

@@ -1,162 +1,91 @@
-use std::fmt;
 use std::io;
 use std::num::ParseIntError;
+use thiserror::Error;
 
-macro_rules! convert_error {
-    ($type: ty, $super_type: ident, $pattern: ident) => {
-        impl From<$type> for $super_type {
-            fn from(x: $type) -> $super_type {
-                $super_type::$pattern(x)
-            }
-        }
-    };
-}
-
+#[derive(Error, Debug)]
 pub enum TopLevelError {
-    IOError(io::Error),
+    #[error("IO error encountered ({source})")]
+    IOError {
+        #[from]
+        source: io::Error,
+    },
+    #[error("No input found")]
     NoInputFound,
+    #[error("No solution found")]
     NoSolutionFound,
+    #[error("Unknown error occurred")]
     UnknownError,
-    PassportParseError(PassportParseError),
-    SeatParseError(SeatParseError),
-    BaggageParseError(BaggageRuleParseError),
+    #[error("Failed to parse passport: {source}")]
+    PassportParseErrorPassport {
+        #[from]
+        source: PassportParseError,
+    },
+    #[error("Failed to parse seat: {source}")]
+    SeatParseError {
+        #[from]
+        source: SeatParseError,
+    },
+    #[error("Failed to parse baggage rule: {source}")]
+    BaggageParseError {
+        #[from]
+        source: BaggageRuleParseError,
+    },
 }
 
-impl fmt::Display for TopLevelError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            TopLevelError::IOError(e) => write!(f, "IO error: {}", e),
-            TopLevelError::NoInputFound => write!(f, "No valid inputs found"),
-            TopLevelError::NoSolutionFound => write!(f, "No solution found."),
-            TopLevelError::PassportParseError(p) => write!(f, "Error parsing passport: {}", p),
-            TopLevelError::SeatParseError(s) => write!(f, "Error parsing seat: {}", s),
-            TopLevelError::BaggageParseError(e) => write!(f, "Error parsing baggage rule: {}", e),
-            TopLevelError::UnknownError => {
-                write!(f, "Unknown error occurred; this shouldn't be possible.")
-            }
-        }
-    }
-}
-
-convert_error!(io::Error, TopLevelError, IOError);
-
+#[derive(Error, Debug)]
 pub enum PasswordParseError {
-    StringToIntError(ParseIntError),
-    NomError(nom::Err<()>),
+    #[error("Failed to convert string to integer: {source}")]
+    StringToIntError {
+        #[from]
+        source: ParseIntError,
+    },
+    #[error("Error nomnomnoming: {source}")]
+    NomError {
+        #[from]
+        source: nom::Err<()>,
+    },
 }
 
-impl fmt::Display for PasswordParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            PasswordParseError::NomError(e) => write!(f, "Parse error: {}", e),
-            PasswordParseError::StringToIntError(e) => {
-                write!(f, "Error converting string to integer: {}", e)
-            }
-        }
-    }
-}
-
-convert_error!(ParseIntError, PasswordParseError, StringToIntError);
-convert_error!(nom::Err<()>, PasswordParseError, NomError);
-
+#[derive(Error, Debug)]
 pub enum MapParseError {
+    #[error("Unexpected character: {0}")]
     UnexpectedCharacter(char),
+    #[error("Uneven width at line {0}")]
     UnevenLines(usize),
 }
 
-impl fmt::Display for MapParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            MapParseError::UnevenLines(l) => write!(f, "Map has uneven width at line {}", l),
-            MapParseError::UnexpectedCharacter(c) => {
-                write!(f, "Unexpected character parsing map: {}", c)
-            }
-        }
-    }
-}
-
+#[derive(Error, Debug)]
 pub enum PassportParseError {
+    #[error("Invalid chunk in passport line: {0}")]
     InvalidChunk(String),
+    #[error("Invalid field in passport: {0}")]
     InvalidField(String),
 }
 
-impl fmt::Display for PassportParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            PassportParseError::InvalidChunk(s) => {
-                write!(f, "Invalid chunk in passport line: {}", s)
-            }
-            PassportParseError::InvalidField(s) => write!(f, "Invalid field in passport: {}", s),
-        }
-    }
-}
-
-convert_error!(PassportParseError, TopLevelError, PassportParseError);
-
-#[derive(Debug, PartialEq)]
+#[derive(Error, Debug, PartialEq)]
 pub enum SeatParseError {
+    #[error("Invalid seat identifier: {0}")]
     InvalidSeatIdentifier(String),
+    #[error("Bad row section size {0}")]
     BadSeatRowSectionSize(usize),
+    #[error("Bad column section size {0}")]
     BadSeatColumnSectionSize(usize),
+    #[error("Unexpected row character '{0}'")]
     UnexpectedRowCharacter(char),
+    #[error("Unexpected column character '{0}'")]
     UnexpectedColumnCharacter(char),
+    #[error("Wasn't able to resolve column for '{0}'")]
     DidNotResolveColumn(String),
+    #[error("Wasn't able to resolve row for '{0}'")]
     DidNotResolveRow(String),
 }
 
-impl fmt::Display for SeatParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            SeatParseError::InvalidSeatIdentifier(s) => {
-                write!(f, "Invalid seat identifier: {:?}", s)
-            }
-            SeatParseError::BadSeatRowSectionSize(x) => write!(
-                f,
-                "Bad identifiers for rows; expected 7 characters, got {}",
-                x
-            ),
-            SeatParseError::BadSeatColumnSectionSize(x) => write!(
-                f,
-                "Bad identifiers for columns; expected 3 characters, got {}",
-                x
-            ),
-            SeatParseError::UnexpectedRowCharacter(c) => {
-                write!(f, "Unexpected character when parsing rows: {:?}", c)
-            }
-            SeatParseError::UnexpectedColumnCharacter(c) => {
-                write!(f, "Unexpected character when parsing columns: {:?}", c)
-            }
-            SeatParseError::DidNotResolveRow(s) => {
-                write!(f, "Could not resolve row with {:?}", s)
-            }
-            SeatParseError::DidNotResolveColumn(s) => {
-                write!(f, "Could not resolve row with {:?}", s)
-            }
-        }
-    }
-}
-
-convert_error!(SeatParseError, TopLevelError, SeatParseError);
-
+#[derive(Error, Debug)]
 pub enum BaggageRuleParseError {
+    #[error("Error parsing rule: {0}")]
     NomError(String),
-    NumericConversionError(ParseIntError),
 }
 
-impl fmt::Display for BaggageRuleParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            BaggageRuleParseError::NomError(e) => write!(f, "General parsing error: {}", e),
-            BaggageRuleParseError::NumericConversionError(e) => {
-                write!(f, "Error converting number to value: {}", e)
-            }
-        }
-    }
-}
-
-convert_error!(BaggageRuleParseError, TopLevelError, BaggageParseError);
-convert_error!(ParseIntError, BaggageRuleParseError, NumericConversionError);
-
 impl<'a> From<nom::Err<nom::error::Error<&'a str>>> for BaggageRuleParseError {
     fn from(x: nom::Err<nom::error::Error<&'a str>>) -> BaggageRuleParseError {
         match x {