Backup commit

My backspace key started ghosting. Nothing works atm.

src/foreign/error.rs

@@ -0,0 +1,68 @@
+use std::error::Error;
+use std::fmt::{Debug, Display};
+use std::sync::Arc;
+
+use dyn_clone::DynClone;
+
+use crate::location::CodeLocation;
+
+/// Errors produced by external code
+pub trait ExternError: Display + Send + Sync + DynClone {
+  /// Convert into trait object
+  #[must_use]
+  fn rc(self) -> Arc<dyn ExternError>
+  where Self: 'static + Sized {
+    Arc::new(self)
+  }
+}
+
+impl Debug for dyn ExternError {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "ExternError({self})")
+  }
+}
+
+impl Error for dyn ExternError {}
+
+/// An error produced by Rust code called form Orchid. The error is type-erased.
+pub type ExternResult<T> = Result<T, Arc<dyn ExternError>>;
+
+/// Some expectation (usually about the argument types of a function) did not
+/// hold.
+#[derive(Clone)]
+pub struct AssertionError {
+  location: CodeLocation,
+  message: &'static str,
+  details: String,
+}
+
+impl AssertionError {
+  /// Construct, upcast and wrap in a Result that never succeeds for easy
+  /// short-circuiting
+  pub fn fail<T>(
+    location: CodeLocation,
+    message: &'static str,
+    details: String,
+  ) -> ExternResult<T> {
+    Err(Self::ext(location, message, details))
+  }
+
+  /// Construct and upcast to [ExternError]
+  pub fn ext(
+    location: CodeLocation,
+    message: &'static str,
+    details: String,
+  ) -> Arc<dyn ExternError> {
+    Self { location, message, details }.rc()
+  }
+}
+
+impl Display for AssertionError {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "Error: expected {}", self.message)?;
+    write!(f, " at {}", self.location)?;
+    write!(f, " details: {}", self.details)
+  }
+}
+
+impl ExternError for AssertionError {}