record, tag, alias errors

- duplicate fields and tags are reported
- circular aliases are reported

compiler/problem/src/can.rs

@@ -1,6 +1,6 @@
 use inlinable_string::InlinableString;
 use roc_collections::all::MutSet;
-use roc_module::ident::Ident;
+use roc_module::ident::{Ident, Lowercase, TagName};
 use roc_module::symbol::{ModuleId, Symbol};
 use roc_parse::operator::BinOp;
 use roc_parse::pattern::PatternType;
@@ -21,6 +21,27 @@ pub enum Problem {
         original_region: Region,
         shadow: Located<Ident>,
     },
+    CyclicAlias(Symbol, Region, Vec<Symbol>),
+    PhantomTypeArgument {
+        alias: Symbol,
+        variable_region: Region,
+        variable_name: Lowercase,
+    },
+    DuplicateRecordFieldValue {
+        field_name: Lowercase,
+        record_region: Region,
+        field_region: Region,
+    },
+    DuplicateRecordFieldType {
+        field_name: Lowercase,
+        record_region: Region,
+        field_region: Region,
+    },
+    DuplicateTag {
+        tag_name: TagName,
+        tag_union_region: Region,
+        tag_region: Region,
+    },
     RuntimeError(RuntimeError),
 }