The pipeline is finally reasonably clean

src/error/conflicting_roles.rs

@@ -0,0 +1,31 @@
+use itertools::Itertools;
+
+use super::{ErrorPosition, ProjectError};
+use crate::utils::BoxedIter;
+use crate::{Location, VName};
+
+/// Error raised if the same name ends up assigned to more than one thing.
+/// A name in Orchid has exactly one meaning, either a value or a module.
+pub struct ConflictingRoles {
+  /// Name assigned to multiple things
+  pub name: VName,
+  /// Location of at least two occurrences
+  pub locations: Vec<Location>,
+}
+impl ProjectError for ConflictingRoles {
+  fn description(&self) -> &str {
+    "The same name is assigned multiple times to conflicting items"
+  }
+  fn message(&self) -> String {
+    format!(
+      "{} has multiple conflicting meanings",
+      self.name.iter().map(|t| t.as_str()).join("::")
+    )
+  }
+  fn positions(&self) -> BoxedIter<ErrorPosition> {
+    Box::new(
+      (self.locations.iter())
+        .map(|l| ErrorPosition { location: l.clone(), message: None }),
+    )
+  }
+}