End-to-end testing of the compile path.

src/backend/error.rs

@@ -18,6 +18,8 @@ pub enum BackendError {
     SetError(#[from] SetError),
     #[error(transparent)]
     LookupError(#[from] LookupError),
+    #[error(transparent)]
+    Write(#[from] cranelift_object::object::write::Error),
 }
 
 impl From<BackendError> for Diagnostic<usize> {
@@ -41,6 +43,41 @@ impl From<BackendError> for Diagnostic<usize> {
             BackendError::LookupError(me) => {
                 Diagnostic::error().with_message(format!("Internal error: {}", me))
             }
+            BackendError::Write(me) => {
+                Diagnostic::error().with_message(format!("Cranelift object write error: {}", me))
+            }
+        }
+    }
+}
+
+impl PartialEq for BackendError {
+    fn eq(&self, other: &Self) -> bool {
+        match self {
+            BackendError::BuiltinError(a) => match other {
+                BackendError::BuiltinError(b) => a == b,
+                _ => false,
+            },
+
+            BackendError::CodegenError(_) => matches!(other, BackendError::CodegenError(_)),
+
+            BackendError::Cranelift(_) => matches!(other, BackendError::Cranelift(_)),
+
+            BackendError::LookupError(a) => match other {
+                BackendError::LookupError(b) => a == b,
+                _ => false,
+            },
+
+            BackendError::SetError(a) => match other {
+                BackendError::SetError(b) => a == b,
+                _ => false,
+            },
+
+            BackendError::VariableLookupFailure => other == &BackendError::VariableLookupFailure,
+
+            BackendError::Write(a) => match other {
+                BackendError::Write(b) => a == b,
+                _ => false,
+            },
         }
     }
 }