Recover Erroneous in type

crates/compiler/solve/src/solve.rs

@@ -3040,7 +3040,6 @@ fn type_to_variable<'a>(
                     alias_variable,
                     AliasKind::Structural,
                 );
-                // let result = register(subs, rank, pools, content);
                 let result = register_with_known_var(subs, destination, rank, pools, content);
 
                 // We only want to unify the actual_var with the alias once
@@ -3054,7 +3053,11 @@ fn type_to_variable<'a>(
                 result
             }
             Erroneous => {
-                let content = Content::Error;
+                // TODO: remove `Erroneous`, `Error` can always be used, and type problems known at
+                // this point can be reported during canonicalization.
+                let problem_index =
+                    SubsIndex::push_new(&mut subs.problems, types.get_problem(&typ).clone());
+                let content = Content::Structure(FlatType::Erroneous(problem_index));
 
                 register_with_known_var(subs, destination, rank, pools, content)
             }

crates/compiler/types/src/types.rs

@@ -417,6 +417,7 @@ pub enum TypeTag {
     Variable(Variable),
     RangedNumber(NumericRange),
     /// A type error, which will code gen to a runtime error
+    /// The problem is at the index of the type tag
     Erroneous,
 
     // TypeExtension is implicit in the type slice
@@ -507,6 +508,11 @@ impl Types {
             .expect("typ is not a single tag union")
     }
 
+    #[track_caller]
+    pub fn get_problem(&self, typ: &Index<TypeTag>) -> &Problem {
+        self.problems.get(typ).expect("typ is not an error")
+    }
+
     pub fn record_fields_slices(
         &self,
         fields: RecordFields,