[fine] Multi-module compilation

It's a little bit complicated, loading a module is a two-step dance
but here's how it's done. Probably some surface-area refactoring needs
to happen so that we do the right thing.

fine/src/semantics.rs

@@ -116,6 +116,12 @@ impl From<u64> for ModuleId {
     }
 }
 
+impl fmt::Display for ModuleId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "#{}", self.0)
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct ImportRecord {
     pub name: String,
@@ -762,6 +768,12 @@ impl Semantics {
         self.import_map.set(imports).expect("imports already set");
     }
 
+    pub fn import_ids(&self) -> Vec<ModuleId> {
+        // TODO: Pull from by_name when we go global
+        let import_map = self.import_map.get().unwrap();
+        import_map.by_id.keys().map(|id| *id).collect()
+    }
+
     pub fn import_by_id(&self, mid: ModuleId) -> Option<Rc<Semantics>> {
         // TODO: ACTUALLY THIS IS WRONG, WE NEED THE GLOBAL MAP HERE, NOT THE LOCAL ONE.
         let import_map = self.import_map.get()?;
@@ -815,6 +827,10 @@ impl Semantics {
         }
     }
 
+    pub fn mid(&self) -> ModuleId {
+        self.mid
+    }
+
     fn report_error_span<T>(&self, start_pos: usize, end_pos: usize, error: T) -> Rc<Error>
     where
         T: ToString,