Refactor type errors back into macro annotations

Far less verbose than defining classes by hand, plus, it allows to have everything about a single error be co-located. And finally, it allows to use 'related', 'label' and so on more easily.

crates/aiken-lang/src/tipo/fields.rs

@@ -27,12 +27,14 @@ impl FieldMap {
                 if self.is_function {
                     Err(Error::DuplicateArgument {
                         label,
-                        locations: vec![*location, location_other],
+                        location: *location,
+                        duplicate_location: location_other,
                     })
                 } else {
                     Err(Error::DuplicateField {
                         label,
-                        locations: vec![*location, location_other],
+                        location: *location,
+                        duplicate_location: location_other,
                     })
                 }
             }
@@ -102,7 +104,7 @@ impl FieldMap {
                 }
             };
 
-            let (position, other_location) = match self.fields.get(label) {
+            let (position, duplicate_location) = match self.fields.get(label) {
                 None => {
                     unknown_labels.push((label.clone(), location));
 
@@ -122,7 +124,8 @@ impl FieldMap {
             } else {
                 if seen_labels.contains(label) {
                     return Err(Error::DuplicateArgument {
-                        locations: vec![location, other_location],
+                        location,
+                        duplicate_location,
                         label: label.to_string(),
                     });
                 }

crates/aiken-project/src/error.rs

@@ -404,6 +404,28 @@ impl Diagnostic for Error {
             Error::UnknownPackageVersion { .. } => None,
         }
     }
+
+    fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn Diagnostic> + 'a>> {
+        match self {
+            Error::DuplicateModule { .. } => None,
+            Error::FileIo { .. } => None,
+            Error::ImportCycle { .. } => None,
+            Error::List { .. } => None,
+            Error::Parse { .. } => None,
+            Error::Type { error, .. } => error.related(),
+            Error::StandardIo(_) => None,
+            Error::MissingManifest { .. } => None,
+            Error::TomlLoading { .. } => None,
+            Error::Format { .. } => None,
+            Error::ValidatorMustReturnBool { .. } => None,
+            Error::WrongValidatorArity { .. } => None,
+            Error::TestFailure { .. } => None,
+            Error::Http { .. } => None,
+            Error::ZipExtract { .. } => None,
+            Error::JoinError { .. } => None,
+            Error::UnknownPackageVersion { .. } => None,
+        }
+    }
 }
 
 #[derive(thiserror::Error)]