Allow `tryEval` to catch `import` parse errors

## Is your feature request related to a problem? I want to use nixd to get options completion for modules I'm working on. Some of the files that are being edited might be incomplete and cause parsing errors. But I want nixd to still use valid modules to provide option completion. I've tried writing this code to skip modules that cannot be parsed: ```nix lib.evalModules { modules = if ignore-parse-errors then allModules |> builtins.concatMap ( modPath: let res = builtins.tryEval (import modPath); mod = lib.setDefaultModuleLocation modPath res.value; in if res.success then [ mod ] else [ ] ) else allModules; }; ``` and found out that `builtins.tryEval` cannot catch parsing errors from `import`. ## Proposed solution Allow `tryEval` to catch `import` parse errors. ## Alternative solutions nixd uses nix's libexpr. Alternative solution would be to let nixd somehow hook `EvalState::parse` to recover from parsing errors. ## Additional context Similar issue asking for ability to catch parsing errors in toml and json files: https://github.com/NixOS/nix/issues/8810 ## Checklist <!-- make sure this issue is not redundant or obsolete --> - [x] checked [latest Nix manual] \([source]) - [x] checked [open feature issues and pull requests] for possible duplicates - [x] reviewed the [contributing guide] [latest Nix manual]: https://nix.dev/manual/nix/development/ [source]: https://github.com/NixOS/nix/tree/master/doc/manual/source [open feature issues and pull requests]: https://github.com/NixOS/nix/labels/feature [contributing guide]: https://github.com/NixOS/nix/blob/master/CONTRIBUTING.md --- Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).