message: Make FileLoader robust to the addition of dupe on &T
  Summary: We really should have Dupe for &T. We can't, because it breaks a linter, but when we fix the linter we'll prefer Starlark not to break.
diff: @@ -37,7 +37,7 @@ pub struct ReturnFileLoader<'a> {
  impl<'a> FileLoader for ReturnFileLoader<'a> {
  fn load(&mut self, path: &str) -> anyhow::Result<FrozenModule> {
  match self.modules.get(path) {
  - Some(v) => Ok(v.dupe()),
  + Some(v) => Ok((*v).dupe()),
  None => Err(anyhow!(
  "ReturnFileLoader does not know the module `{}`",
  path
  