alias referenced by another alias is not unused!

compiler/can/src/def.rs

@@ -184,17 +184,11 @@ pub fn canonicalize_defs<'a>(
                 let mut can_ann =
                     canonicalize_annotation(env, &mut scope, &ann.value, ann.region, var_store);
 
-                // all referenced symbols in an alias must be symbols
+                // Record all the annotation's references in output.references.lookups
-                output
+                for symbol in can_ann.references {
-                    .references
+                    output.references.lookups.insert(symbol);
-                    .referenced_aliases
+                    output.references.referenced_aliases.insert(symbol);
-                    .extend(can_ann.aliases.keys().copied());
+                }
-
-                // if an alias definition uses an alias, the used alias is referenced
-                output
-                    .references
-                    .lookups
-                    .extend(can_ann.aliases.keys().copied());
 
                 let mut can_vars: Vec<Located<(Lowercase, Variable)>> =
                     Vec::with_capacity(vars.len());

compiler/reporting/tests/test_reporting.rs

@@ -3880,4 +3880,26 @@ mod test_reporting {
             ),
         )
     }
+
+    #[test]
+    fn alias_using_alias() {
+        report_problem_as(
+            indoc!(
+                r#"
+                # The color of a node. Leaves are considered Black.
+                NodeColor : [ Red, Black ]
+
+                Dict k v : [ Node NodeColor k v (Dict k v) (Dict k v), Empty ]
+
+                # Create an empty dictionary.
+                empty : Dict k v
+                empty =
+                    Empty
+
+                empty
+                "#
+            ),
+            "",
+        )
+    }
 }