feat: Ensure packages always have modules at the root

hugr-core/src/package.rs

@@ -219,7 +219,7 @@ fn to_module_hugr(mut hugr: Hugr) -> Result<Hugr, PackageError> {
 }
 
 /// Error raised while loading a package.
-#[derive(Debug, Display, Error)]
+#[derive(Debug, Display, Error, PartialEq)]
 #[non_exhaustive]
 pub enum PackageError {
  /// A hugr in the package does not have an [OpType::Module] root.
@@ -262,10 +262,12 @@ pub enum PackageValidationError {
 
 #[cfg(test)]
 mod test {
+ use cool_asserts::assert_matches;
+
  use crate::builder::test::{
  simple_cfg_hugr, simple_dfg_hugr, simple_funcdef_hugr, simple_module_hugr,
  };
- use crate::extension::ExtensionId;
+ use crate::extension::{ExtensionId, EMPTY_REG};
  use crate::ops::dataflow::IOTrait;
  use crate::ops::Input;
 
@@ -310,7 +312,7 @@ mod test {
  #[case::cfg(simple_cfg_hugr(), false)]
  #[case::unsupported_input(simple_input_node(), true)]
  fn hugr_to_package(#[case] hugr: Hugr, #[case] errors: bool) {
- match (Package::from_hugr(hugr), errors) {
+ match (&Package::from_hugr(hugr.clone()), errors) {
  (Ok(package), false) => {
  assert_eq!(package.modules.len(), 1);
  let root_op = package.modules[0].get_optype(package.modules[0].root());
@@ -320,4 +322,24 @@ mod test {
  (p, _) => panic!("Unexpected result {:?}", p),
  }
  }
+
+ #[rstest]
+ fn package_properties() {
+ let module = simple_module_hugr();
+ let dfg = simple_dfg_hugr();
+
+ assert_matches!(
+ Package::new([module.clone(), dfg.clone()], []),
+ Err(PackageError::NonModuleHugr {
+ module_index: 1,
+ root_op: OpType::DFG(_),
+ })
+ );
+
+ let mut pkg = Package::from_hugrs([module, dfg], []).unwrap();
+ let mut reg = EMPTY_REG.clone();
+ pkg.validate(&mut reg).unwrap();
+
+ assert_eq!(pkg.modules.len(), 2);
+ }
 }