feat: add rust-script

external/rust-script/src/error.rs

@@ -0,0 +1,61 @@
+/*!
+Definition of the program's main error type.
+*/
+
+use std::borrow::Cow;
+use std::error::Error;
+use std::fmt;
+use std::io;
+use std::result::Result;
+
+/// Shorthand for the program's common result type.
+pub type MainResult<T> = Result<T, MainError>;
+
+/// An error in the program.
+#[derive(Debug)]
+pub enum MainError {
+    Io(io::Error),
+    Tag(Cow<'static, str>, Box<MainError>),
+    Other(Box<dyn Error>),
+    OtherOwned(String),
+    OtherBorrowed(&'static str),
+}
+
+impl fmt::Display for MainError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        use self::MainError::*;
+        use std::fmt::Display;
+        match *self {
+            Io(ref err) => Display::fmt(err, fmt),
+            Tag(ref msg, ref err) => write!(fmt, "{}: {}", msg, err),
+            Other(ref err) => Display::fmt(err, fmt),
+            OtherOwned(ref err) => Display::fmt(err, fmt),
+            OtherBorrowed(err) => Display::fmt(err, fmt),
+        }
+    }
+}
+
+impl Error for MainError {}
+
+macro_rules! from_impl {
+    ($src_ty:ty => $dst_ty:ty, $src:ident -> $e:expr) => {
+        impl From<$src_ty> for $dst_ty {
+            fn from($src: $src_ty) -> $dst_ty {
+                $e
+            }
+        }
+    };
+}
+
+from_impl! { io::Error => MainError, v -> MainError::Io(v) }
+from_impl! { String => MainError, v -> MainError::OtherOwned(v) }
+from_impl! { &'static str => MainError, v -> MainError::OtherBorrowed(v) }
+
+impl<T> From<Box<T>> for MainError
+where
+    T: 'static + Error,
+{
+    fn from(src: Box<T>) -> Self {
+        MainError::Other(src)
+    }
+}