Decide how to handle unreachable resolve cases

crates/frontend/src/resolve.rs

@@ -169,7 +169,7 @@ pub fn expr<'db>(
     use ir::ExprKind::*;
     let kind = match &expr.kind {
         // directly translate existing value definitions
-        // TODO: symbols are unresolved, handle unreachability better?
+        // symbols are unreachable, so we can ignore them
         Value(value) => Value(value.clone()),
 
         // recursively descend into unary operations
@@ -212,14 +212,8 @@ pub fn expr<'db>(
             ast::ExprExtra::Aggregate(agg) => todo!(),
         },
 
-        // TODO: handle unreachability better?
-        Variable(idx) => Variable(*idx),
-
-        // TODO: handle unreachability better?
-        Load { relation, query } => Load {
-            relation: *relation,
-            query: query.clone(),
-        },
+        // other variants should be unreachable
+        other => unreachable!("unreachable AST expression kind: {other:#?}"),
     };
 
     // construct converted expression
@@ -230,7 +224,6 @@ pub fn expr<'db>(
 }
 
 /// Resolve a reference to a relation by name.
-// TODO: track incrementally?
 pub fn relation_name<'db>(db: &'db dyn Database, name: ast::Name) -> RelationLabel<'db> {
     todo!()
 }