flake-edit 0.3.6

use crate::error::Error;
use crate::follows::{AttrPath, Segment};
use serde::{Deserialize, Deserializer};
use std::collections::HashMap;
use std::fs::File;
use std::io::Read;
use std::path::{Path, PathBuf};

/// Errors that arise from parsing or walking `flake.lock`.
///
/// Each variant pinpoints a distinct shape failure: a missing field, a
/// follows cycle, or a node that the resolver cannot find. The variants
/// carry the smallest contextual data (segment path, node key) that lets
/// the caller reconstruct the failure without reparsing the message.
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum LockError {
    /// `flake.lock` did not parse as JSON.
    #[error("failed to parse flake.lock as json")]
    Parse(#[from] serde_json::Error),
    /// The lockfile has no `root` node referenced by `nodes`.
    #[error("flake.lock is missing the root node")]
    MissingRoot,
    /// The root node carries no `inputs`, so a path cannot be walked.
    #[error("flake.lock root has no inputs")]
    RootHasNoInputs,
    /// An intermediate input on the path has no sub-inputs.
    #[error("input '{path}' has no sub-inputs in flake.lock")]
    InputHasNoSubInputs { path: String },
    /// A path segment does not resolve to a declared input.
    #[error("input '{path}' not found in flake.lock")]
    InputNotFound { path: String },
    /// A `follows` declaration with an empty target was encountered while
    /// walking. Surfaced as a hard failure when the path needs a target.
    #[error("input '{path}' has no follows target")]
    FollowsTargetMissing { path: String },
    /// The node referenced by a path segment is absent from the `nodes` map.
    #[error("could not find lockfile node '{node}' referenced by input '{path}'")]
    NodeMissingForPath { node: String, path: String },
    /// The node looked up directly by name is absent.
    #[error("could not find lockfile node '{node}'")]
    NodeMissing { node: String },
    /// Recursion budget exhausted while resolving a follows path.
    #[error("cycle while resolving follows path")]
    FollowsCycle,
    /// A node has no `locked` block (so no `rev` can be retrieved).
    #[error("lockfile node has no locked information")]
    NodeNotLocked,
    /// A locked block has no `rev`.
    #[error("locked node has no rev")]
    LockedHasNoRev,
}

/// A nested input discovered in `flake.lock` with its existing follows
/// target, if any.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct NestedInput {
    /// Dotted path to the nested input (e.g. `crane.nixpkgs`).
    pub path: AttrPath,
    /// Existing follows target, if the input is redirected.
    pub follows: Option<AttrPath>,
    /// Original flake URL for `Direct` references (e.g.
    /// `github:nixos/nixpkgs/nixos-unstable`). `None` for follows-only
    /// references.
    pub url: Option<String>,
}

impl NestedInput {
    /// Render as `path\tfollows_target` (or just `path` when the input has no
    /// follows target). The tab separator lets the UI style each side
    /// independently.
    pub fn to_display_string(&self) -> String {
        match &self.follows {
            Some(target) => format!("{}\t{}", self.path, target),
            None => self.path.to_string(),
        }
    }
}

/// Parsed `flake.lock`. Loaded with [`Self::from_default_path`],
/// [`Self::from_file`], or [`Self::read_from_str`].
#[derive(Debug, Deserialize)]
pub struct FlakeLock {
    nodes: HashMap<String, Node>,
    root: String,
}

/// A single entry in the lockfile's `nodes` map.
#[derive(Debug, Deserialize)]
pub(crate) struct Node {
    inputs: Option<HashMap<String, Input>>,
    locked: Option<Locked>,
    original: Option<Original>,
}

impl Node {
    fn rev(&self) -> Result<String, LockError> {
        self.locked.as_ref().ok_or(LockError::NodeNotLocked)?.rev()
    }
}

/// Reference from a node's `inputs` map.
///
/// Lockfile shape:
/// - `"name"` is a direct reference to another node, parsed as
///   [`Self::Direct`].
/// - `["a", "b", ...]` is a follows path with a target, parsed as
///   `Indirect(Some(path))`.
/// - `[]` is a follows declaration with no target (Nix emits this when an
///   upstream chain has overridden the input to nothing, e.g. a lockfile
///   whose source `flake.nix` carries
///   `nix.inputs.flake-compat.follows = "";`), parsed as `Indirect(None)`.
#[derive(Debug, Clone)]
pub enum Input {
    Direct(String),
    Indirect(Option<AttrPath>),
}

impl<'de> Deserialize<'de> for Input {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        use serde::de::{Error, SeqAccess, Visitor};
        use std::fmt;

        struct InputVisitor;

        impl<'de> Visitor<'de> for InputVisitor {
            type Value = Input;

            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
                f.write_str(
                    "a node name string, an empty array, or an array of \
                     non-empty segment names",
                )
            }

            fn visit_str<E: Error>(self, v: &str) -> Result<Self::Value, E> {
                Ok(Input::Direct(v.to_string()))
            }

            fn visit_string<E: Error>(self, v: String) -> Result<Self::Value, E> {
                Ok(Input::Direct(v))
            }

            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
            where
                A: SeqAccess<'de>,
            {
                // Empty `[]` is a real lockfile shape: `inputs.X = []`
                // marks an input whose follows chain has been overridden
                // away. Surface it as `Indirect(None)` instead of an
                // error.
                let Some(first) = seq.next_element::<String>()? else {
                    return Ok(Input::Indirect(None));
                };
                let first_seg = Segment::from_unquoted(first).map_err(A::Error::custom)?;
                let mut path = AttrPath::new(first_seg);
                while let Some(raw) = seq.next_element::<String>()? {
                    let seg = Segment::from_unquoted(raw).map_err(A::Error::custom)?;
                    path.push(seg);
                }
                Ok(Input::Indirect(Some(path)))
            }
        }

        deserializer.deserialize_any(InputVisitor)
    }
}

/// Locked metadata for a node. Only [`Self::rev`] is consumed by the
/// crate; the other JSON coordinates (`owner`, `repo`, `type`, `narHash`,
/// ...) are ignored on parse.
#[derive(Debug, Deserialize, Clone)]
pub(crate) struct Locked {
    rev: Option<String>,
}

impl Locked {
    fn rev(&self) -> Result<String, LockError> {
        self.rev.clone().ok_or(LockError::LockedHasNoRev)
    }
}

/// Original (pre-lock) reference for a node, as written in the source
/// flake. One variant per flakeref shape Nix produces in `flake.lock`.
#[derive(Debug)]
pub(crate) enum Original {
    Github {
        owner: String,
        repo: String,
        ref_field: Option<String>,
    },
    Gitlab {
        owner: String,
        repo: String,
        ref_field: Option<String>,
    },
    Sourcehut {
        owner: String,
        repo: String,
        ref_field: Option<String>,
    },
    Git {
        url: String,
        ref_field: Option<String>,
    },
    Hg {
        url: String,
        ref_field: Option<String>,
    },
    Tarball {
        url: String,
    },
    File {
        url: String,
    },
    Path {
        path: String,
    },
    Indirect {
        id: String,
        ref_field: Option<String>,
    },
    /// Flakeref `type` not recognized by this crate. Tolerated because
    /// Nix adds new schemes occasionally; lockfiles that mention one
    /// should still parse so the rest of the inputs stay usable.
    /// Malformed payloads of recognized types surface as `D::Error`,
    /// not here.
    Unknown {
        node_type: String,
    },
}

impl<'de> Deserialize<'de> for Original {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        use serde::de::Error;

        #[derive(Deserialize)]
        struct ForgePayload {
            owner: String,
            repo: String,
            #[serde(rename = "ref")]
            ref_field: Option<String>,
        }
        #[derive(Deserialize)]
        struct VcsPayload {
            url: String,
            #[serde(rename = "ref")]
            ref_field: Option<String>,
        }
        #[derive(Deserialize)]
        struct UrlPayload {
            url: String,
        }
        #[derive(Deserialize)]
        struct PathPayload {
            path: String,
        }
        #[derive(Deserialize)]
        struct IndirectPayload {
            id: String,
            #[serde(rename = "ref")]
            ref_field: Option<String>,
        }

        let value = serde_json::Value::deserialize(deserializer)?;
        let node_type = value
            .get("type")
            .and_then(serde_json::Value::as_str)
            .ok_or_else(|| D::Error::missing_field("type"))?
            .to_string();

        fn payload<T: for<'a> Deserialize<'a>, E: Error>(value: serde_json::Value) -> Result<T, E> {
            serde_json::from_value(value).map_err(E::custom)
        }

        Ok(match node_type.as_str() {
            "github" => {
                let ForgePayload {
                    owner,
                    repo,
                    ref_field,
                } = payload(value)?;
                Original::Github {
                    owner,
                    repo,
                    ref_field,
                }
            }
            "gitlab" => {
                let ForgePayload {
                    owner,
                    repo,
                    ref_field,
                } = payload(value)?;
                Original::Gitlab {
                    owner,
                    repo,
                    ref_field,
                }
            }
            "sourcehut" => {
                let ForgePayload {
                    owner,
                    repo,
                    ref_field,
                } = payload(value)?;
                Original::Sourcehut {
                    owner,
                    repo,
                    ref_field,
                }
            }
            "git" => {
                let VcsPayload { url, ref_field } = payload(value)?;
                Original::Git { url, ref_field }
            }
            "hg" => {
                let VcsPayload { url, ref_field } = payload(value)?;
                Original::Hg { url, ref_field }
            }
            "tarball" => {
                let UrlPayload { url } = payload(value)?;
                Original::Tarball { url }
            }
            "file" => {
                let UrlPayload { url } = payload(value)?;
                Original::File { url }
            }
            "path" => {
                let PathPayload { path } = payload(value)?;
                Original::Path { path }
            }
            "indirect" => {
                let IndirectPayload { id, ref_field } = payload(value)?;
                Original::Indirect { id, ref_field }
            }
            _ => Original::Unknown { node_type },
        })
    }
}

impl Original {
    /// Reconstruct a flake URL from the original reference. Returns
    /// `None` for [`Original::Unknown`], which also logs a
    /// `tracing::warn!` naming the unrecognized type.
    fn to_flake_url(&self) -> Option<String> {
        match self {
            Original::Github {
                owner,
                repo,
                ref_field,
            } => Some(forge_flake_url("github", owner, repo, ref_field.as_deref())),
            Original::Gitlab {
                owner,
                repo,
                ref_field,
            } => Some(forge_flake_url("gitlab", owner, repo, ref_field.as_deref())),
            Original::Sourcehut {
                owner,
                repo,
                ref_field,
            } => Some(forge_flake_url(
                "sourcehut",
                owner,
                repo,
                ref_field.as_deref(),
            )),
            Original::Git { url, ref_field } => {
                Some(prefixed_vcs_url("git+", url, ref_field.as_deref()))
            }
            Original::Hg { url, ref_field } => {
                Some(prefixed_vcs_url("hg+", url, ref_field.as_deref()))
            }
            Original::Tarball { url } | Original::File { url } => Some(url.clone()),
            Original::Path { path } => Some(format!("path:{path}")),
            Original::Indirect { id, ref_field } => {
                Some(indirect_flake_url(id, ref_field.as_deref()))
            }
            Original::Unknown { node_type } => {
                tracing::warn!(
                    "Unknown flake.lock node type '{node_type}'; cannot reconstruct flake URL"
                );
                None
            }
        }
    }
}

/// Build a `<scheme>:<owner>/<repo>[/<ref>]` URL, the shape shared by
/// `github`, `gitlab`, and `sourcehut` flakerefs.
fn forge_flake_url(scheme: &str, owner: &str, repo: &str, ref_field: Option<&str>) -> String {
    let mut url = format!("{scheme}:{owner}/{repo}");
    if let Some(r) = ref_field {
        url.push('/');
        url.push_str(r);
    }
    url
}

/// Prepend `git+` / `hg+` to a VCS transport URL and append `?ref=<r>`.
///
/// Nix keeps unrecognized query parameters (e.g. `?dir=subdir`) inside
/// the lockfile's `url` field, so the input may already carry a `?`.
/// Append with `&` in that case to avoid producing a flakeref with two
/// `?`, which Nix's URL parser rejects.
fn prefixed_vcs_url(scheme_prefix: &str, url: &str, ref_field: Option<&str>) -> String {
    let Some(r) = ref_field else {
        return format!("{scheme_prefix}{url}");
    };
    let separator = if url.contains('?') { '&' } else { '?' };
    format!("{scheme_prefix}{url}{separator}ref={r}")
}

/// Indirect refs encode `ref` as a path component (`flake:<id>/<ref>`),
/// not a query parameter. Other VCS schemes use `?ref=`; the indirect
/// scheme is the odd one out and easy to get wrong.
fn indirect_flake_url(id: &str, ref_field: Option<&str>) -> String {
    match ref_field {
        Some(r) => format!("flake:{id}/{r}"),
        None => format!("flake:{id}"),
    }
}

// Per-thread `nested_inputs` call counter. A `follow` invocation must walk
// the immutable lockfile once and thread the result through every consumer;
// tests reset this and assert the walk count. Thread-local so parallel test
// threads do not contend.
#[cfg(test)]
thread_local! {
    pub(crate) static NESTED_INPUTS_CALLS: std::cell::Cell<usize> =
        const { std::cell::Cell::new(0) };
}

impl FlakeLock {
    const LOCK: &'static str = "flake.lock";

    /// Load `flake.lock` from the current directory.
    pub fn from_default_path() -> Result<Self, Error> {
        let path = PathBuf::from(Self::LOCK);
        Self::from_file(path)
    }

    /// Load and parse a lockfile from `path`.
    pub fn from_file<P: AsRef<Path>>(path: P) -> Result<Self, Error> {
        let path = path.as_ref();
        let mut file = File::open(path).map_err(|source| Error::Read {
            path: path.to_path_buf(),
            source,
        })?;
        let mut contents = String::new();
        file.read_to_string(&mut contents)
            .map_err(|source| Error::Read {
                path: path.to_path_buf(),
                source,
            })?;
        Self::read_from_str(&contents)
    }

    /// Parse lockfile JSON from `str`.
    pub fn read_from_str(str: &str) -> Result<Self, Error> {
        serde_json::from_str(str).map_err(|e| Error::Lock(LockError::Parse(e)))
    }

    /// Name of the root node.
    pub fn root(&self) -> &str {
        &self.root
    }

    /// Resolve an [`AttrPath`] to the node key it ultimately points at,
    /// walking the lock tree from `root`.
    ///
    /// [`Input::Indirect`] entries are `follows` paths of input *names*
    /// rooted at the lock root, not node keys, so encountering one restarts
    /// the walk from root with that path plus any remaining segments.
    fn resolve_input_path(&self, path: &AttrPath) -> Result<String, LockError> {
        // Bound recursion: a valid lock file has no follows cycles, but we
        // still guard against malformed input.
        const MAX_HOPS: usize = 64;
        self.resolve_input_path_inner(path.segments(), MAX_HOPS)
    }

    /// `segments` is non-empty by construction: callers either forward an
    /// [`AttrPath`]'s segments or prepend an [`Input::Indirect`] follows
    /// path, both of which are non-empty.
    fn resolve_input_path_inner(
        &self,
        segments: &[Segment],
        budget: usize,
    ) -> Result<String, LockError> {
        if budget == 0 {
            return Err(LockError::FollowsCycle);
        }

        let mut current_key = self.root.clone();
        let mut current_node = self.nodes.get(self.root()).ok_or(LockError::MissingRoot)?;

        for (i, segment) in segments.iter().enumerate() {
            let inputs = current_node.inputs.as_ref().ok_or_else(|| {
                if i == 0 {
                    LockError::RootHasNoInputs
                } else {
                    let prefix: Vec<_> = segments[..i].iter().map(|s| s.as_str()).collect();
                    LockError::InputHasNoSubInputs {
                        path: prefix.join("."),
                    }
                }
            })?;

            let resolved = inputs.get(segment.as_str()).ok_or_else(|| {
                let prefix: Vec<_> = segments[..=i].iter().map(|s| s.as_str()).collect();
                LockError::InputNotFound {
                    path: prefix.join("."),
                }
            })?;

            match resolved {
                Input::Direct(node_key) => {
                    current_key = node_key.clone();
                }
                Input::Indirect(Some(follows_path)) => {
                    let mut new_path: Vec<Segment> = follows_path.segments().to_vec();
                    new_path.extend(segments[i + 1..].iter().cloned());
                    return self.resolve_input_path_inner(&new_path, budget - 1);
                }
                Input::Indirect(None) => {
                    let prefix: Vec<_> = segments[..=i].iter().map(|s| s.as_str()).collect();
                    return Err(LockError::FollowsTargetMissing {
                        path: prefix.join("."),
                    });
                }
            }

            if i + 1 < segments.len() {
                current_node = self.nodes.get(&current_key).ok_or_else(|| {
                    let prefix: Vec<_> = segments[..=i].iter().map(|s| s.as_str()).collect();
                    LockError::NodeMissingForPath {
                        node: current_key.clone(),
                        path: prefix.join("."),
                    }
                })?;
            }
        }

        Ok(current_key)
    }

    /// Resolve `path` to its locked revision.
    ///
    /// # Errors
    ///
    /// Returns a [`Error::Lock`] wrapping the underlying
    /// [`LockError`] if any segment is missing in the lock graph, the
    /// resolved node is not present, or it carries no `rev`.
    pub fn rev_for(&self, path: &AttrPath) -> Result<String, Error> {
        let node_name = self.resolve_input_path(path)?;
        let node = self
            .nodes
            .get(&node_name)
            .ok_or_else(|| LockError::NodeMissing {
                node: node_name.clone(),
            })?;
        Ok(node.rev()?)
    }

    /// All nested inputs reachable from the root, with their existing
    /// follows targets.
    ///
    /// Walks `flake.lock` recursively from the root, emitting one entry per
    /// `inputs.X` on any descendant node and building the path
    /// segment-by-segment. Capped at [`NESTED_INPUTS_MAX_DEPTH`]. Cycles in
    /// the node graph are broken by a visited set keyed on node name.
    ///
    /// Output is sorted by path for stable emission order.
    pub fn nested_inputs(&self) -> Vec<NestedInput> {
        #[cfg(test)]
        NESTED_INPUTS_CALLS.with(|c| c.set(c.get() + 1));

        let mut inputs = Vec::new();
        let Some(root_node) = self.nodes.get(&self.root) else {
            return inputs;
        };
        let Some(root_inputs) = &root_node.inputs else {
            return inputs;
        };

        for (top_level_name, top_level_ref) in root_inputs {
            let node_name = match top_level_ref {
                Input::Direct(name) => name.clone(),
                // Indirect top-level inputs have no sub-inputs to descend
                // into. Their follows edges still appear via the recursive
                // walker on the `Direct` siblings that own them.
                Input::Indirect(_) => continue,
            };
            let Ok(parent_seg) = Segment::from_unquoted(top_level_name.clone()) else {
                continue;
            };
            let path = AttrPath::new(parent_seg);
            let mut visited: HashMap<String, ()> = HashMap::new();
            visited.insert(node_name.clone(), ());
            self.collect_nested_inputs_recursive(&node_name, &path, 1, &mut visited, &mut inputs);
        }

        inputs.sort_by(|a, b| a.path.cmp(&b.path));
        inputs
    }

    /// Descend through `node_name`, emitting one [`NestedInput`] per declared
    /// sub-input up to [`NESTED_INPUTS_MAX_DEPTH`].
    fn collect_nested_inputs_recursive(
        &self,
        node_name: &str,
        parent_path: &AttrPath,
        depth: usize,
        visited: &mut HashMap<String, ()>,
        out: &mut Vec<NestedInput>,
    ) {
        if depth >= NESTED_INPUTS_MAX_DEPTH {
            return;
        }
        let Some(node) = self.nodes.get(node_name) else {
            return;
        };
        let Some(node_inputs) = &node.inputs else {
            return;
        };

        // Iterate sub-inputs in lex order so emission is deterministic.
        let mut keys: Vec<&String> = node_inputs.keys().collect();
        keys.sort();
        for nested_name in keys {
            let nested_ref = node_inputs.get(nested_name).unwrap();
            let Ok(nested_seg) = Segment::from_unquoted(nested_name.clone()) else {
                continue;
            };
            let mut path = parent_path.clone();
            path.push(nested_seg);

            let (follows, url, descend_into) = match nested_ref {
                Input::Indirect(Some(target)) => (Some(target.clone()), None, None),
                // Empty `[]` declarations have no follows target. Emit
                // the input with `follows: None` so the path is still
                // visible to the UI.
                Input::Indirect(None) => (None, None, None),
                Input::Direct(child_node_name) => {
                    let url = self
                        .nodes
                        .get(child_node_name.as_str())
                        .and_then(|n| n.original.as_ref())
                        .and_then(|o| o.to_flake_url());
                    (None, url, Some(child_node_name.clone()))
                }
            };

            out.push(NestedInput {
                path: path.clone(),
                follows,
                url,
            });

            if let Some(child) = descend_into {
                if visited.contains_key(&child) {
                    continue;
                }
                visited.insert(child.clone(), ());
                self.collect_nested_inputs_recursive(&child, &path, depth + 1, visited, out);
                visited.remove(&child);
            }
        }
    }
}

/// Maximum recursion depth for [`FlakeLock::nested_inputs`]. Backstops
/// pathological cycles in malformed lockfiles.
pub const NESTED_INPUTS_MAX_DEPTH: usize = 64;
#[cfg(test)]
mod tests {
    use super::*;

    fn minimal_lock() -> &'static str {
        r#"
    {
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1718714799,
        "narHash": "sha256-FUZpz9rg3gL8NVPKbqU8ei1VkPLsTIfAJ2fdAf5qjak=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "c00d587b1a1afbf200b1d8f0b0e4ba9deb1c7f0e",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs"
      }
    }
  },
  "root": "root",
  "version": 7
}
    "#
    }
    fn minimal_independent_lock_no_overrides() -> &'static str {
        r#"
    {
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1721138476,
        "narHash": "sha256-+W5eZOhhemLQxelojLxETfbFbc19NWawsXBlapYpqIA=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "ad0b5eed1b6031efaed382844806550c3dcb4206",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1719690277,
        "narHash": "sha256-0xSej1g7eP2kaUF+JQp8jdyNmpmCJKRpO12mKl/36Kc=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "2741b4b489b55df32afac57bc4bfd220e8bf617e",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs",
        "treefmt-nix": "treefmt-nix"
      }
    },
    "treefmt-nix": {
      "inputs": {
        "nixpkgs": "nixpkgs_2"
      },
      "locked": {
        "lastModified": 1721382922,
        "narHash": "sha256-GYpibTC0YYKRpFR9aftym9jjRdUk67ejw1IWiaQkaiU=",
        "owner": "numtide",
        "repo": "treefmt-nix",
        "rev": "50104496fb55c9140501ea80d183f3223d13ff65",
        "type": "github"
      },
      "original": {
        "owner": "numtide",
        "repo": "treefmt-nix",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}
    "#
    }

    fn minimal_independent_lock_nixpkgs_overridden() -> &'static str {
        r#"
    {
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1721138476,
        "narHash": "sha256-+W5eZOhhemLQxelojLxETfbFbc19NWawsXBlapYpqIA=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "ad0b5eed1b6031efaed382844806550c3dcb4206",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixos-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs",
        "treefmt-nix": "treefmt-nix"
      }
    },
    "treefmt-nix": {
      "inputs": {
        "nixpkgs": [
          "nixpkgs"
        ]
      },
      "locked": {
        "lastModified": 1721382922,
        "narHash": "sha256-GYpibTC0YYKRpFR9aftym9jjRdUk67ejw1IWiaQkaiU=",
        "owner": "numtide",
        "repo": "treefmt-nix",
        "rev": "50104496fb55c9140501ea80d183f3223d13ff65",
        "type": "github"
      },
      "original": {
        "owner": "numtide",
        "repo": "treefmt-nix",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}
    "#
    }

    #[test]
    fn parse_minimal() {
        let minimal_lock = minimal_lock();
        FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
    }
    /// The lockfile's top-level `"version"` field is not validated. A
    /// wildly unsupported version (e.g. `99`) must still parse cleanly
    /// so this crate can read whatever shape Nix produces.
    #[test]
    fn parse_ignores_unknown_version() {
        let lock = r#"{
  "nodes": { "root": { "inputs": {} } },
  "root": "root",
  "version": 99
}"#;
        FlakeLock::read_from_str(lock).expect("unknown version must still parse");
    }
    #[test]
    fn parse_minimal_root() {
        let minimal_lock = minimal_lock();
        let parsed_lock =
            FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
        assert_eq!("root", parsed_lock.root);
    }
    #[test]
    fn minimal_ref() {
        let minimal_lock = minimal_lock();
        let parsed_lock =
            FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
        assert_eq!(
            "c00d587b1a1afbf200b1d8f0b0e4ba9deb1c7f0e",
            parsed_lock
                .rev_for(&"nixpkgs".parse().unwrap())
                .expect("Id: nixpkgs is in the lockfile.")
        );
    }
    #[test]
    fn parse_minimal_independent_lock_no_overrides() {
        let minimal_lock = minimal_independent_lock_no_overrides();
        FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
    }
    #[test]
    fn minimal_independent_lock_no_overrides_ref() {
        let minimal_lock = minimal_independent_lock_no_overrides();
        let parsed_lock =
            FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
        assert_eq!(
            "ad0b5eed1b6031efaed382844806550c3dcb4206",
            parsed_lock
                .rev_for(&"nixpkgs".parse().unwrap())
                .expect("Id: nixpkgs is in the lockfile.")
        );
    }
    #[test]
    fn parse_minimal_independent_lock_nixpkgs_overridden() {
        let minimal_lock = minimal_independent_lock_nixpkgs_overridden();
        FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
    }

    #[test]
    fn rev_for_sub_input_path_missing_parent_returns_error() {
        let minimal_lock = minimal_lock();
        let parsed_lock =
            FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
        assert!(
            parsed_lock
                .rev_for(&"browseros.nixpkgs".parse().unwrap())
                .is_err()
        );
    }

    #[test]
    fn rev_for_sub_input_path_resolves() {
        let lock = minimal_independent_lock_no_overrides();
        let parsed = FlakeLock::read_from_str(lock).expect("Should be parsed correctly.");
        assert_eq!(
            "2741b4b489b55df32afac57bc4bfd220e8bf617e",
            parsed
                .rev_for(&"treefmt-nix.nixpkgs".parse().unwrap())
                .expect("Should resolve sub-input path")
        );
    }

    #[test]
    fn rev_for_sub_input_follows_resolves() {
        let lock = minimal_independent_lock_nixpkgs_overridden();
        let parsed = FlakeLock::read_from_str(lock).expect("Should be parsed correctly.");
        assert_eq!(
            parsed.rev_for(&"nixpkgs".parse().unwrap()).unwrap(),
            parsed
                .rev_for(&"treefmt-nix.nixpkgs".parse().unwrap())
                .expect("Should resolve followed sub-input")
        );
    }

    #[test]
    fn rev_for_quoted_id() {
        // Quoted attribute names like `"nixpkgs-24.11"` from `list --format simple`
        // should be stripped before lock lookup.
        let minimal_lock = minimal_lock();
        let parsed_lock =
            FlakeLock::read_from_str(minimal_lock).expect("Should be parsed correctly.");
        assert_eq!(
            parsed_lock.rev_for(&"nixpkgs".parse().unwrap()).unwrap(),
            parsed_lock
                .rev_for(&"\"nixpkgs\"".parse().unwrap())
                .unwrap(),
        );
    }

    #[test]
    fn rev_for_node_without_locked_returns_error() {
        let lock = r#"{
  "nodes": {
    "root": {
      "inputs": { "bare": "bare" }
    },
    "bare": {
      "original": { "owner": "o", "repo": "r", "type": "github" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        assert!(parsed.rev_for(&"bare".parse().unwrap()).is_err());
    }

    #[test]
    fn rev_for_node_without_rev_returns_error() {
        // `path` is set only so the `original` block deserializes; this
        // test is about missing `locked.rev`.
        let lock = r#"{
  "nodes": {
    "root": {
      "inputs": { "norev": "norev" }
    },
    "norev": {
      "locked": { "lastModified": 1, "narHash": "", "type": "path" },
      "original": { "type": "path", "path": "/tmp/norev" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        assert!(parsed.rev_for(&"norev".parse().unwrap()).is_err());
    }

    #[test]
    fn nested_input_path_quotes_dots() {
        let lock = r#"{
  "nodes": {
    "hls-1.10": {
      "inputs": { "nixpkgs": "nixpkgs_2" },
      "flake": false,
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "abc", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "abc", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs_2": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "def", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": {
      "inputs": { "hls-1.10": "hls-1.10", "nixpkgs": "nixpkgs" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        let nested = parsed.nested_inputs();
        assert_eq!(nested.len(), 1);
        assert_eq!(nested[0].path.to_string(), "\"hls-1.10\".nixpkgs");
    }

    #[test]
    fn nested_inputs_recurses_to_grandchild() {
        // The walker descends through `Direct` children, so a depth-2
        // nested input (root → neovim → nixvim → flake-parts) must be
        // emitted with a 3-segment path. This exercises the recursive
        // path-stack code in `collect_nested_inputs_recursive`.
        let lock = r#"{
  "nodes": {
    "flake-parts": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "a", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "flake-parts_2": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "b", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "neovim": {
      "inputs": { "nixvim": "nixvim" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "c", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixvim": {
      "inputs": { "flake-parts": "flake-parts_2" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "d", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": {
      "inputs": { "flake-parts": "flake-parts", "neovim": "neovim" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        let nested = parsed.nested_inputs();
        let paths: Vec<String> = nested.iter().map(|n| n.path.to_string()).collect();
        assert!(
            paths.contains(&"neovim.nixvim".to_string()),
            "depth-1 path missing, got: {paths:?}"
        );
        assert!(
            paths.contains(&"neovim.nixvim.flake-parts".to_string()),
            "depth-2 path missing, got: {paths:?}"
        );
    }

    #[test]
    fn nested_inputs_terminates_on_cyclic_lockfile() {
        // A pathological lock graph where node A's input recurses back
        // into A itself must not loop forever. The visited-set in
        // `collect_nested_inputs_recursive` short-circuits the cycle.
        let lock = r#"{
  "nodes": {
    "a": {
      "inputs": { "b": "b" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "a", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "b": {
      "inputs": { "a": "a" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "b", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": { "inputs": { "a": "a" } }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        let nested = parsed.nested_inputs();
        assert!(!nested.is_empty());
        assert!(
            nested
                .iter()
                .all(|n| n.path.len() <= NESTED_INPUTS_MAX_DEPTH)
        );
    }

    #[test]
    fn rev_for_quoted_sub_input_path() {
        let lock = r#"{
  "nodes": {
    "hls-1.10": {
      "inputs": { "nixpkgs": "nixpkgs_2" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "abc", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "abc", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs_2": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "def", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": {
      "inputs": { "hls-1.10": "hls-1.10", "nixpkgs": "nixpkgs" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        assert_eq!(
            "def",
            parsed
                .rev_for(&"\"hls-1.10\".nixpkgs".parse().unwrap())
                .expect("Should resolve quoted sub-input path")
        );
    }

    /// An `Indirect` follows path names *inputs* from the lock root, not node
    /// keys. Resolution must go through `root.inputs`, which may map e.g.
    /// `nixpkgs` to a node keyed `nixpkgs_2`.
    #[test]
    fn rev_for_indirect_resolves_via_root_inputs() {
        let lock = r#"{
  "nodes": {
    "nixpkgs_2": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "treefmt-nix": {
      "inputs": { "nixpkgs": ["nixpkgs"] },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": {
      "inputs": { "nixpkgs": "nixpkgs_2", "treefmt-nix": "treefmt-nix" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        // treefmt-nix.nixpkgs follows ["nixpkgs"], i.e. root.inputs.nixpkgs,
        // which is node "nixpkgs_2". There is no node literally named "nixpkgs".
        assert_eq!(
            "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
            parsed
                .rev_for(&"treefmt-nix.nixpkgs".parse().unwrap())
                .expect("indirect follows must resolve through root.inputs, not by node name")
        );
    }

    /// A multi-segment follows path like `["crane", "nixpkgs"]` must be walked
    /// segment-by-segment from root, since each hop can map to a renamed node key.
    #[test]
    fn rev_for_indirect_multi_segment_path() {
        let lock = r#"{
  "nodes": {
    "nixpkgs": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "1111111111111111111111111111111111111111", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs_2": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "2222222222222222222222222222222222222222", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "crane": {
      "inputs": { "nixpkgs": "nixpkgs_2" },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "cccccccccccccccccccccccccccccccccccccccc", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "devshell": {
      "inputs": { "nixpkgs": ["crane", "nixpkgs"] },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "dddddddddddddddddddddddddddddddddddddddd", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": {
      "inputs": { "nixpkgs": "nixpkgs", "crane": "crane", "devshell": "devshell" }
    }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).unwrap();
        // devshell.nixpkgs follows ["crane","nixpkgs"] -> node "nixpkgs_2" (rev 222...),
        // NOT root's "nixpkgs" node (rev 111...).
        assert_eq!(
            "2222222222222222222222222222222222222222",
            parsed
                .rev_for(&"devshell.nixpkgs".parse().unwrap())
                .expect("multi-segment indirect follows must be walked from root")
        );
    }

    /// Walk every `inputs` map and collect each `Indirect` follows target as
    /// a vector of segment strings. Used by the fixture parse tests below.
    fn collect_indirect_targets(lock: &FlakeLock) -> Vec<(String, String, Vec<String>)> {
        let mut out: Vec<(String, String, Vec<String>)> = Vec::new();
        for (node_name, node) in &lock.nodes {
            let Some(inputs) = node.inputs.as_ref() else {
                continue;
            };
            for (input_name, input_ref) in inputs {
                if let Input::Indirect(Some(path)) = input_ref {
                    let segs: Vec<String> = path
                        .segments()
                        .iter()
                        .map(|s| s.as_str().to_string())
                        .collect();
                    out.push((node_name.clone(), input_name.clone(), segs));
                }
            }
        }
        out.sort();
        out
    }

    /// `depth_upstream_redundant_depth3.flake.lock` has three `Indirect`
    /// entries forming the upstream-propagation chain: `omnibus.nixpkgs`
    /// follows `["nixpkgs"]`, the depth-2 follows `["omnibus", "nixpkgs"]`,
    /// and the depth-3 follows `["omnibus", "flops", "nixpkgs"]`.
    #[test]
    fn fixture_depth_upstream_redundant_depth3_parses_indirects() {
        let lock_text =
            std::fs::read_to_string("tests/fixtures/depth_upstream_redundant_depth3.flake.lock")
                .expect("fixture present");
        let lock = FlakeLock::read_from_str(&lock_text).expect("fixture parses");
        let mut segs_only: Vec<Vec<String>> = collect_indirect_targets(&lock)
            .into_iter()
            .map(|(_, _, segs)| segs)
            .collect();
        segs_only.sort();
        assert_eq!(
            segs_only,
            vec![
                vec!["nixpkgs".to_string()],
                vec![
                    "omnibus".to_string(),
                    "flops".to_string(),
                    "nixpkgs".to_string()
                ],
                vec!["omnibus".to_string(), "nixpkgs".to_string()],
            ],
            "Indirect entries must be decoded with their full structural depth",
        );
    }

    /// `depth_upstream_partial.flake.lock` covers a deeper mix of Indirect
    /// shapes; verify each one is decoded into a non-empty `AttrPath` whose
    /// segments are valid Nix names (no embedded quotes / control chars).
    #[test]
    fn fixture_depth_upstream_partial_parses_indirects() {
        let lock_text = std::fs::read_to_string("tests/fixtures/depth_upstream_partial.flake.lock")
            .expect("fixture present");
        let lock = FlakeLock::read_from_str(&lock_text).expect("fixture parses");
        let entries = collect_indirect_targets(&lock);
        assert!(
            entries.len() >= 3,
            "fixture has at least three Indirect arrays, got {}",
            entries.len()
        );
        for (node, input, segs) in &entries {
            assert!(
                !segs.is_empty(),
                "{node}.{input}: Indirect path must be non-empty",
            );
            for seg in segs {
                assert!(
                    !seg.is_empty() && !seg.contains('"'),
                    "{node}.{input}: segment `{seg}` must be a valid Nix name",
                );
            }
        }
    }

    /// `dot_ancestor_cycle.flake.lock` exercises the dotted-segment case:
    /// the lockfile node `hls-1.10` is reachable through the typed
    /// `AttrPath`, even though a literal dot in the segment forces source-
    /// form quoting at the `flake.nix` boundary.
    #[test]
    fn fixture_dot_ancestor_cycle_parses_indirects_with_dotted_node() {
        let lock_text = std::fs::read_to_string("tests/fixtures/dot_ancestor_cycle.flake.lock")
            .expect("fixture present");
        let lock = FlakeLock::read_from_str(&lock_text).expect("fixture parses");
        // Direct walk: the dotted node `hls-1.10` exists and its
        // `Indirect` `["helper"]` entry is decoded as a one-segment path.
        let hls = lock.nodes.get("hls-1.10").expect("hls-1.10 node");
        let inputs = hls.inputs.as_ref().expect("hls-1.10 has inputs");
        match inputs.get("helper").expect("helper input present") {
            Input::Indirect(Some(path)) => {
                let segs: Vec<&str> = path.segments().iter().map(|s| s.as_str()).collect();
                assert_eq!(segs, vec!["helper"]);
            }
            Input::Indirect(None) => panic!("expected Indirect(Some), got Indirect(None)"),
            Input::Direct(name) => panic!("expected Indirect, got Direct({name})"),
        }
    }

    /// Empty `[]` follows arrays mark an input whose follows chain has
    /// been overridden away (e.g. a lockfile entry `inputs.flake-compat
    /// = []`). The deserializer must accept them and store them as
    /// `Indirect(None)`.
    #[test]
    fn indirect_empty_array_is_accepted_as_none() {
        let lock = r#"{
  "nodes": {
    "child": {
      "inputs": { "disabled": [] },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "x", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": { "inputs": { "child": "child" } }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).expect("empty Indirect must parse");
        let child = parsed.nodes.get("child").expect("child node");
        let inputs = child.inputs.as_ref().expect("child has inputs");
        match inputs.get("disabled").expect("disabled input present") {
            Input::Indirect(None) => {}
            other => panic!("expected Indirect(None), got {other:?}"),
        }
    }

    /// A top-level input (`nix`) whose nested inputs map mixes
    /// [`Input::Direct`] references, non-empty
    /// [`Input::Indirect`] arrays (`["nixpkgs"]`), and empty `[]`
    /// declarations must parse cleanly. [`FlakeLock::nested_inputs`]
    /// emits one entry per declaration; entries built from `[]` carry
    /// `follows: None`.
    #[test]
    fn nested_inputs_handles_mixed_direct_indirect_and_empty() {
        let lock = r#"{
  "nodes": {
    "flake-parts": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "fp", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nix": {
      "inputs": {
        "flake-compat": [],
        "flake-parts": "flake-parts",
        "nixpkgs": ["nixpkgs"]
      },
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "n", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "nixpkgs": {
      "locked": { "lastModified": 1, "narHash": "", "owner": "o", "repo": "r", "rev": "np", "type": "github" },
      "original": { "owner": "o", "repo": "r", "type": "github" }
    },
    "root": { "inputs": { "nix": "nix", "nixpkgs": "nixpkgs" } }
  },
  "root": "root",
  "version": 7
}"#;
        let parsed = FlakeLock::read_from_str(lock).expect("mixed-shape lock parses");
        let nested = parsed.nested_inputs();
        let by_path: std::collections::HashMap<String, &NestedInput> =
            nested.iter().map(|n| (n.path.to_string(), n)).collect();

        let disabled = by_path
            .get("nix.flake-compat")
            .expect("empty Indirect emitted as nested input");
        assert!(
            disabled.follows.is_none(),
            "empty `[]` must surface as follows: None, got {:?}",
            disabled.follows
        );

        let resolved = by_path
            .get("nix.nixpkgs")
            .expect("non-empty Indirect emitted as nested input");
        assert_eq!(
            resolved.follows.as_ref().map(|p| p.to_string()),
            Some("nixpkgs".to_string()),
            "non-empty Indirect must surface its follows target",
        );
    }

    /// A bare `https://...` parses as a `tarball` flakeref, not a
    /// `git` repo, so the missing `git+` prefix is a silent corruption
    /// rather than a parse error.
    #[test]
    fn to_flake_url_git_type_prepends_scheme() {
        let o = Original::Git {
            url: "https://git.clan.lol/clan/munix".to_string(),
            ref_field: None,
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("git+https://git.clan.lol/clan/munix"),
        );
    }

    /// Loss of `ref` would unpin the reconstructed URL from the branch
    /// the lock captured.
    #[test]
    fn to_flake_url_git_with_ref_appends_query() {
        let o = Original::Git {
            url: "https://git.example.com/repo".to_string(),
            ref_field: Some("main".to_string()),
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("git+https://git.example.com/repo?ref=main"),
        );
    }

    /// The lockfile type is `"hg"` (not `"mercurial"`); the previous
    /// spelling silently matched no input and dropped every hg
    /// promotion.
    #[test]
    fn to_flake_url_hg_type_prepends_scheme() {
        let o = Original::Hg {
            url: "https://hg.example.com/repo".to_string(),
            ref_field: None,
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("hg+https://hg.example.com/repo"),
        );
    }

    /// `original.url` may already carry a `?` (Nix only strips
    /// recognized params like `ref` / `shallow`; the rest stay
    /// in-band). Appending `?ref=` would produce two `?`, which Nix
    /// rejects.
    #[test]
    fn to_flake_url_git_with_existing_query_appends_with_ampersand() {
        let o = Original::Git {
            url: "https://git.example.com/repo?dir=subdir".to_string(),
            ref_field: Some("main".to_string()),
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("git+https://git.example.com/repo?dir=subdir&ref=main"),
        );
    }

    #[test]
    fn to_flake_url_tarball_returns_url_unchanged() {
        let o = Original::Tarball {
            url: "https://channels.nixos.org/nixos-25.05/nixexprs.tar.xz".to_string(),
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("https://channels.nixos.org/nixos-25.05/nixexprs.tar.xz"),
        );
    }

    #[test]
    fn to_flake_url_path_uses_path_field() {
        let o = Original::Path {
            path: "/etc/nixos".to_string(),
        };
        assert_eq!(o.to_flake_url().as_deref(), Some("path:/etc/nixos"));
    }

    #[test]
    fn to_flake_url_indirect_uses_id_field() {
        let o = Original::Indirect {
            id: "nixpkgs".to_string(),
            ref_field: None,
        };
        assert_eq!(o.to_flake_url().as_deref(), Some("flake:nixpkgs"));
    }

    /// Indirect refs use a path component (`flake:<id>/<ref>`) rather
    /// than the `?ref=` query the VCS schemes use; pin the test on
    /// that asymmetry.
    #[test]
    fn to_flake_url_indirect_with_ref_appends_path_component() {
        let o = Original::Indirect {
            id: "nixpkgs".to_string(),
            ref_field: Some("nixos-25.05".to_string()),
        };
        assert_eq!(
            o.to_flake_url().as_deref(),
            Some("flake:nixpkgs/nixos-25.05"),
        );
    }

    /// Unrecognized `type` strings deserialize to [`Original::Unknown`]
    /// and [`Original::to_flake_url`] returns `None`.
    #[test]
    fn to_flake_url_unknown_type_returns_none() {
        let o: Original = serde_json::from_str(r#"{"type": "future-type"}"#).unwrap();
        assert!(matches!(&o, Original::Unknown { node_type } if node_type == "future-type"));
        assert_eq!(o.to_flake_url(), None);
    }

    /// Malformed payload of a recognized type must be a parse error, not
    /// a silent fall-through to [`Original::Unknown`]. The error message
    /// must name the missing field so the failure is actionable.
    #[test]
    fn malformed_known_type_is_a_parse_error() {
        let err = serde_json::from_str::<Original>(r#"{"type": "github"}"#).unwrap_err();
        assert!(
            err.to_string().contains("owner"),
            "error must name the missing field, got: {err}",
        );
    }

    /// A node with `original.type` absent is malformed at the protocol
    /// level. Surface it as a parse error rather than coercing to
    /// `Unknown { node_type: "" }`.
    #[test]
    fn missing_type_is_a_parse_error() {
        let err = serde_json::from_str::<Original>(r#"{}"#).unwrap_err();
        assert!(
            err.to_string().contains("type"),
            "error must name the missing field, got: {err}",
        );
    }
}