Flutsch

🚧🚧🚧 Under construction 🚧🚧🚧

This tool is not production ready yet.

A recursive nix value introspection tool.

Flutsch is a dynamic and efficient tool designed to traverse any generic Nix expression (attribute sets) easily.

It introspects nested attributes and functions, presenting dynamic value information in a JSON format (position, value type, etc.). This output can be used for further static analysis tasks, including but not limited to inspection of documentation comments.

Try it out:

nix run github:hsjobeki/flutsch <path/to/file.nix>

This will create a file values.json in your current directory.

Flutsch was designed as generic expression treewalker with the boobytraps and footguns of nixpkgs in mind.

since it leverages the native C++ Nix evaluator. It catches all kinds of evaluation errors; and more importantly, it can provide introspection without adding more builtins / changing the nix language itself.

Demo

Example

rec {
  a = {
    # The id function
    inherit a;
  };
}

Which essentially contains three entries:

The root attrset rec {...}
The binding for a = ...
The recursive binding inherit a

Theoretically there would also be a value a.a.a and so on. But flutsch terminates here since it has already introspected all the values.

The result looks then like this:

[
    {
        "binding": {
            "is_root": false,
            "name": "a",
            "pos": {
                "column": 3,
                "file": "test.nix",
                "line": 2
            }
        },
        "value": {
            "children": [
                {
                    "is_root": false,
                    "name": "a",
                    "pos": {
                        "column": 7,
                        "file": "test.nix",
                        "line": 2
                    }
                }
            ],
            "error": false,
            "error_description": null,
            "path": [
                "<root>",
                "a"
            ],
            "pos": {
                "column": 7,
                "file": "test.nix",
                "line": 2
            },
            "type": "attrset"
        }
    },
    {
        "binding": {
            "is_root": true,
            "name": "<root>",
            "pos": {
                "column": 5,
                "file": "test.nix",
                "line": 1
            }
        },
        "value": {
            "children": [
                {
                    "is_root": false,
                    "name": "a",
                    "pos": {
                        "column": 5,
                        "file": "test.nix",
                        "line": 1
                    }
                }
            ],
            "error": false,
            "error_description": null,
            "path": [
                "<root>"
            ],
            "pos": {
                "column": 5,
                "file": "test.nix",
                "line": 1
            },
            "type": "attrset"
        }
    }
]

Which can be used (e.g. via it json representation) for further static analysis, visualization tasks, or generating documentation.

Key Features

Deep Traversal: Effortlessly explores any Nix attribute set without much configuration.
Error Handling: With its native error handling in the C++ Nix evaluator, Flutsch cannot fail.
Introspection Output: The native c++ bindings allow to retrieve information that is internal to the evaluation.
Static Analysis Readiness: Flutsch's output serves as a prime candidate for static analysis, especially for scrutinizing documentation comments and understanding the structure and relations within Nix expressions.

Usage

flutsch ./default.nix

Flutsch can be granularly configured via a json config file:

Simply pass --config <file_path.json> to the invocation.

Contributing

TODO

hsjobeki / flutsch