crates/oxy-core/src/objects.rs at c8f92cc5f89e · andymccall/oxygen

# c8f92cc5f89e oxygen / crates / oxy-core / src / objects.rs
23.2 KiB · Rust · last changed Import the Oxygen specification and the first Rust implementation (root change) 1 month ago source blame history raw
//! Typed objects and their canonical encodings (spec §6, §7, §13.2).
//!
//! Encoding conventions not fixed by the spec text are defined here:
//! - Enum-like items (`TreeOp`, `Edit`) are maps whose key 0 is the variant tag.
//! - An `OpRef`/atom reference is `[bytes32, uint]`; `AtomRef::Start` is `0`
//!   and `AtomRef::End` is `1`.
//! - A `Mode` is an unsigned integer: bit 0 = executable, bit 1 = opaque.
//! - `NodeKind`: 0 = file, 1 = dir, 2 = symlink.

use crate::cbor::{self, Value};
use crate::hash::{hash_object, ChangeHash, KeyId, ObjectRef, ObjectType};
use crate::ids::{ChangeId, NodeId};
use std::collections::BTreeMap;

pub const FORMAT_VERSION: u64 = 1;

#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
pub enum ObjectError {
    #[error("cbor: {0}")]
    Cbor(#[from] cbor::CborError),
    #[error("schema: {0}")]
    Schema(String),
}

pub(crate) fn schema<T>(msg: impl Into<String>) -> Result<T, ObjectError> {
    Err(ObjectError::Schema(msg.into()))
}

pub(crate) type Map = BTreeMap<u64, Value>;

pub(crate) fn field<'a>(m: &'a Map, k: u64, what: &str) -> Result<&'a Value, ObjectError> {
    m.get(&k).ok_or_else(|| ObjectError::Schema(format!("missing field {k} ({what})")))
}
pub(crate) fn uint(v: &Value, what: &str) -> Result<u64, ObjectError> {
    v.as_uint().ok_or_else(|| ObjectError::Schema(format!("{what}: expected unsigned integer")))
}
pub(crate) fn u32_(v: &Value, what: &str) -> Result<u32, ObjectError> {
    u32::try_from(uint(v, what)?).map_err(|_| ObjectError::Schema(format!("{what}: exceeds u32")))
}
pub(crate) fn text<'a>(v: &'a Value, what: &str) -> Result<&'a str, ObjectError> {
    v.as_text().ok_or_else(|| ObjectError::Schema(format!("{what}: expected text")))
}
pub(crate) fn array<'a>(v: &'a Value, what: &str) -> Result<&'a [Value], ObjectError> {
    v.as_array().ok_or_else(|| ObjectError::Schema(format!("{what}: expected array")))
}
pub(crate) fn map<'a>(v: &'a Value, what: &str) -> Result<&'a Map, ObjectError> {
    v.as_map().ok_or_else(|| ObjectError::Schema(format!("{what}: expected map")))
}
pub(crate) fn bytes<'a>(v: &'a Value, what: &str) -> Result<&'a [u8], ObjectError> {
    v.as_bytes().ok_or_else(|| ObjectError::Schema(format!("{what}: expected bytes")))
}
pub(crate) fn oref(v: &Value, what: &str) -> Result<ObjectRef, ObjectError> {
    ObjectRef::from_slice(bytes(v, what)?).ok_or_else(|| ObjectError::Schema(format!("{what}: expected 32 bytes")))
}
pub(crate) fn node_id(v: &Value, what: &str) -> Result<NodeId, ObjectError> {
    NodeId::from_slice(bytes(v, what)?).ok_or_else(|| ObjectError::Schema(format!("{what}: expected 16 bytes")))
}
pub(crate) fn check_version(m: &Map) -> Result<(), ObjectError> {
    let v = uint(field(m, 0, "version")?, "version")?;
    if v != FORMAT_VERSION {
        return schema(format!("unsupported format version {v}"));
    }
    Ok(())
}

// ---------------------------------------------------------------- Hlc

/// Hybrid logical clock (spec §6.4).
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
pub struct Hlc {
    pub wall_ms: u64,
    pub logical: u32,
}

impl Hlc {
    pub fn now() -> Hlc {
        let wall_ms = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_millis() as u64)
            .unwrap_or(0);
        Hlc { wall_ms, logical: 0 }
    }
    pub(crate) fn to_value(self) -> Value {
        Value::map([(0, Value::Uint(self.wall_ms)), (1, Value::Uint(self.logical as u64))])
    }
    pub(crate) fn from_value(v: &Value) -> Result<Hlc, ObjectError> {
        let m = map(v, "hlc")?;
        Ok(Hlc {
            wall_ms: uint(field(m, 0, "hlc.wall_ms")?, "hlc.wall_ms")?,
            logical: u32_(field(m, 1, "hlc.logical")?, "hlc.logical")?,
        })
    }
}

// ---------------------------------------------------------------- tree

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum NodeKind {
    File,
    Dir,
    Symlink,
}

impl NodeKind {
    fn tag(self) -> u64 {
        match self {
            NodeKind::File => 0,
            NodeKind::Dir => 1,
            NodeKind::Symlink => 2,
        }
    }
    fn from_tag(t: u64) -> Result<NodeKind, ObjectError> {
        Ok(match t {
            0 => NodeKind::File,
            1 => NodeKind::Dir,
            2 => NodeKind::Symlink,
            _ => return schema(format!("unknown node kind {t}")),
        })
    }
}

/// Executable bit plus content mode (spec §7.1, §7.5).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default, PartialOrd, Ord)]
pub struct Mode {
    pub exec: bool,
    pub opaque: bool,
}

impl Mode {
    pub const TEXT: Mode = Mode { exec: false, opaque: false };
    pub const OPAQUE: Mode = Mode { exec: false, opaque: true };
    fn bits(self) -> u64 {
        (self.exec as u64) | ((self.opaque as u64) << 1)
    }
    fn from_bits(b: u64) -> Result<Mode, ObjectError> {
        if b > 3 {
            return schema(format!("unknown mode bits {b}"));
        }
        Ok(Mode { exec: b & 1 != 0, opaque: b & 2 != 0 })
    }
}

/// Reference to a tree operation of some change: the placement or mode atom it
/// introduced. `change == ObjectRef::ZERO` means this change.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub struct OpRef {
    pub change: ChangeHash,
    pub index: u32,
}

impl OpRef {
    fn to_value(self) -> Value {
        Value::Array(vec![Value::Bytes(self.change.0.to_vec()), Value::Uint(self.index as u64)])
    }
    fn from_value(v: &Value, what: &str) -> Result<OpRef, ObjectError> {
        let a = array(v, what)?;
        if a.len() != 2 {
            return schema(format!("{what}: expected [hash, index]"));
        }
        Ok(OpRef { change: oref(&a[0], what)?, index: u32_(&a[1], what)? })
    }
    /// Replace a self reference with the concrete change hash.
    pub fn resolve(self, me: ChangeHash) -> OpRef {
        if self.change.is_zero() { OpRef { change: me, ..self } } else { self }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TreeOp {
    AddNode { node: NodeId, kind: NodeKind, mode: Mode, parent: NodeId, name: String },
    RemoveNode { node: NodeId, placement: OpRef },
    Move { node: NodeId, old: OpRef, parent: NodeId, name: String },
    SetMode { node: NodeId, old: OpRef, mode: Mode },
}

/// Names must be valid, non-empty, not `.`/`..`, and free of `/` and NUL (spec §7.1).
pub fn validate_name(name: &str) -> Result<(), ObjectError> {
    if name.is_empty() || name == "." || name == ".." || name.contains('/') || name.contains('\0') {
        return schema(format!("invalid placement name {name:?}"));
    }
    Ok(())
}

impl TreeOp {
    pub fn node(&self) -> NodeId {
        match self {
            TreeOp::AddNode { node, .. }
            | TreeOp::RemoveNode { node, .. }
            | TreeOp::Move { node, .. }
            | TreeOp::SetMode { node, .. } => *node,
        }
    }

    fn to_value(&self) -> Value {
        let nid = |n: &NodeId| Value::Bytes(n.0.to_vec());
        match self {
            TreeOp::AddNode { node, kind, mode, parent, name } => Value::map([
                (0, Value::Uint(0)),
                (1, nid(node)),
                (2, Value::Uint(kind.tag())),
                (3, Value::Uint(mode.bits())),
                (4, nid(parent)),
                (5, Value::Text(name.clone())),
            ]),
            TreeOp::RemoveNode { node, placement } => {
                Value::map([(0, Value::Uint(1)), (1, nid(node)), (2, placement.to_value())])
            }
            TreeOp::Move { node, old, parent, name } => Value::map([
                (0, Value::Uint(2)),
                (1, nid(node)),
                (2, old.to_value()),
                (4, nid(parent)),
                (5, Value::Text(name.clone())),
            ]),
            TreeOp::SetMode { node, old, mode } => Value::map([
                (0, Value::Uint(3)),
                (1, nid(node)),
                (2, old.to_value()),
                (3, Value::Uint(mode.bits())),
            ]),
        }
    }

    fn from_value(v: &Value) -> Result<TreeOp, ObjectError> {
        let m = map(v, "tree_op")?;
        let tag = uint(field(m, 0, "tree_op tag")?, "tree_op tag")?;
        let node = node_id(field(m, 1, "tree_op.node")?, "tree_op.node")?;
        let op = match tag {
            0 => {
                let name = text(field(m, 5, "name")?, "name")?.to_owned();
                validate_name(&name)?;
                TreeOp::AddNode {
                    node,
                    kind: NodeKind::from_tag(uint(field(m, 2, "kind")?, "kind")?)?,
                    mode: Mode::from_bits(uint(field(m, 3, "mode")?, "mode")?)?,
                    parent: node_id(field(m, 4, "parent")?, "parent")?,
                    name,
                }
            }
            1 => TreeOp::RemoveNode { node, placement: OpRef::from_value(field(m, 2, "placement")?, "placement")? },
            2 => {
                let name = text(field(m, 5, "name")?, "name")?.to_owned();
                validate_name(&name)?;
                TreeOp::Move {
                    node,
                    old: OpRef::from_value(field(m, 2, "old")?, "old")?,
                    parent: node_id(field(m, 4, "parent")?, "parent")?,
                    name,
                }
            }
            3 => TreeOp::SetMode {
                node,
                old: OpRef::from_value(field(m, 2, "old")?, "old")?,
                mode: Mode::from_bits(uint(field(m, 3, "mode")?, "mode")?)?,
            },
            _ => return schema(format!("unknown tree op tag {tag}")),
        };
        if node.is_root() {
            return schema("tree op on the root node");
        }
        Ok(op)
    }
}

// ---------------------------------------------------------------- edits

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum AtomRef {
    Start,
    End,
    Atom { change: ChangeHash, index: u32 },
}

impl AtomRef {
    fn to_value(self) -> Value {
        match self {
            AtomRef::Start => Value::Uint(0),
            AtomRef::End => Value::Uint(1),
            AtomRef::Atom { change, index } => {
                Value::Array(vec![Value::Bytes(change.0.to_vec()), Value::Uint(index as u64)])
            }
        }
    }
    fn from_value(v: &Value, what: &str) -> Result<AtomRef, ObjectError> {
        match v {
            Value::Uint(0) => Ok(AtomRef::Start),
            Value::Uint(1) => Ok(AtomRef::End),
            Value::Array(a) if a.len() == 2 => {
                Ok(AtomRef::Atom { change: oref(&a[0], what)?, index: u32_(&a[1], what)? })
            }
            _ => schema(format!("{what}: expected atom reference")),
        }
    }
    pub fn resolve(self, me: ChangeHash) -> AtomRef {
        match self {
            AtomRef::Atom { change, index } if change.is_zero() => AtomRef::Atom { change: me, index },
            other => other,
        }
    }
}

/// Half-open range of atoms introduced by one change.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct AtomRange {
    pub change: ChangeHash,
    pub from: u32,
    pub to: u32,
}

impl AtomRange {
    fn to_value(self) -> Value {
        Value::Array(vec![
            Value::Bytes(self.change.0.to_vec()),
            Value::Uint(self.from as u64),
            Value::Uint(self.to as u64),
        ])
    }
    fn from_value(v: &Value) -> Result<AtomRange, ObjectError> {
        let a = array(v, "atom range")?;
        if a.len() != 3 {
            return schema("atom range: expected [hash, from, to]");
        }
        let r = AtomRange { change: oref(&a[0], "range.change")?, from: u32_(&a[1], "range.from")?, to: u32_(&a[2], "range.to")? };
        if r.from >= r.to {
            return schema("atom range: empty or inverted");
        }
        Ok(r)
    }
    pub fn resolve(self, me: ChangeHash) -> AtomRange {
        if self.change.is_zero() { AtomRange { change: me, ..self } } else { self }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Edit {
    Insert { node: NodeId, after: AtomRef, before: AtomRef, lines: Vec<Vec<u8>> },
    Delete { node: NodeId, atoms: Vec<AtomRange> },
    Replace { node: NodeId, old: Option<ObjectRef>, new: Option<ObjectRef> },
}

impl Edit {
    pub fn node(&self) -> NodeId {
        match self {
            Edit::Insert { node, .. } | Edit::Delete { node, .. } | Edit::Replace { node, .. } => *node,
        }
    }

    fn to_value(&self) -> Value {
        let nid = |n: &NodeId| Value::Bytes(n.0.to_vec());
        let opt = |o: &Option<ObjectRef>| match o {
            Some(r) => Value::Bytes(r.0.to_vec()),
            None => Value::Null,
        };
        match self {
            Edit::Insert { node, after, before, lines } => Value::map([
                (0, Value::Uint(0)),
                (1, nid(node)),
                (2, after.to_value()),
                (3, before.to_value()),
                (4, Value::Array(lines.iter().map(|l| Value::Bytes(l.clone())).collect())),
            ]),
            Edit::Delete { node, atoms } => Value::map([
                (0, Value::Uint(1)),
                (1, nid(node)),
                (2, Value::Array(atoms.iter().map(|r| r.to_value()).collect())),
            ]),
            Edit::Replace { node, old, new } => {
                Value::map([(0, Value::Uint(2)), (1, nid(node)), (2, opt(old)), (3, opt(new))])
            }
        }
    }

    fn from_value(v: &Value) -> Result<Edit, ObjectError> {
        let m = map(v, "edit")?;
        let tag = uint(field(m, 0, "edit tag")?, "edit tag")?;
        let node = node_id(field(m, 1, "edit.node")?, "edit.node")?;
        let opt = |v: &Value, what: &str| -> Result<Option<ObjectRef>, ObjectError> {
            if v.is_null() { Ok(None) } else { Ok(Some(oref(v, what)?)) }
        };
        Ok(match tag {
            0 => {
                let lines = array(field(m, 4, "lines")?, "lines")?
                    .iter()
                    .map(|l| bytes(l, "line").map(|b| b.to_vec()))
                    .collect::<Result<Vec<_>, _>>()?;
                if lines.is_empty() {
                    return schema("insert with no lines");
                }
                Edit::Insert {
                    node,
                    after: AtomRef::from_value(field(m, 2, "after")?, "after")?,
                    before: AtomRef::from_value(field(m, 3, "before")?, "before")?,
                    lines,
                }
            }
            1 => {
                let atoms = array(field(m, 2, "atoms")?, "atoms")?
                    .iter()
                    .map(AtomRange::from_value)
                    .collect::<Result<Vec<_>, _>>()?;
                if atoms.is_empty() {
                    return schema("delete with no atoms");
                }
                Edit::Delete { node, atoms }
            }
            2 => Edit::Replace { node, old: opt(field(m, 2, "old")?, "old")?, new: opt(field(m, 3, "new")?, "new")? },
            _ => return schema(format!("unknown edit tag {tag}")),
        })
    }
}

// ---------------------------------------------------------------- change

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ChangeKind {
    Normal,
    Resolution,
    WorkingCopy,
}

impl ChangeKind {
    fn tag(self) -> u64 {
        match self {
            ChangeKind::Normal => 0,
            ChangeKind::Resolution => 1,
            ChangeKind::WorkingCopy => 2,
        }
    }
    fn from_tag(t: u64) -> Result<ChangeKind, ObjectError> {
        Ok(match t {
            0 => ChangeKind::Normal,
            1 => ChangeKind::Resolution,
            2 => ChangeKind::WorkingCopy,
            _ => return schema(format!("unknown change kind {t}")),
        })
    }
}

/// A change (spec §6.1). `deps` is kept sorted and unique by `normalize`.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Change {
    pub change_id: ChangeId,
    pub deps: Vec<ChangeHash>,
    pub author: KeyId,
    pub hlc: Hlc,
    pub message: String,
    pub tree_ops: Vec<TreeOp>,
    pub edits: Vec<Edit>,
    pub kind: ChangeKind,
}

impl Change {
    pub fn normalize(&mut self) {
        self.deps.sort();
        self.deps.dedup();
    }

    pub fn to_value(&self) -> Value {
        Value::map([
            (0, Value::Uint(FORMAT_VERSION)),
            (1, Value::Bytes(self.change_id.0.to_vec())),
            (2, Value::Array(self.deps.iter().map(|d| Value::Bytes(d.0.to_vec())).collect())),
            (3, Value::Bytes(self.author.0.to_vec())),
            (4, self.hlc.to_value()),
            (5, Value::Text(self.message.clone())),
            (6, Value::Array(self.tree_ops.iter().map(|t| t.to_value()).collect())),
            (7, Value::Array(self.edits.iter().map(|e| e.to_value()).collect())),
            (8, Value::Uint(self.kind.tag())),
            (9, Value::Map(BTreeMap::new())),
        ])
    }

    pub fn encode(&self) -> Vec<u8> {
        debug_assert!(self.deps.windows(2).all(|w| w[0] < w[1]), "deps must be normalized");
        cbor::encode(&self.to_value())
    }

    pub fn hash(&self) -> ChangeHash {
        hash_object(ObjectType::Change, &self.encode())
    }

    pub fn decode(bytes: &[u8]) -> Result<Change, ObjectError> {
        let v = cbor::decode(bytes)?;
        Self::from_value(&v)
    }

    pub fn from_value(v: &Value) -> Result<Change, ObjectError> {
        let m = map(v, "change")?;
        check_version(m)?;
        let change_id = ChangeId::from_slice(bytes(field(m, 1, "change_id")?, "change_id")?)
            .ok_or_else(|| ObjectError::Schema("change_id: expected 16 bytes".into()))?;
        let deps = array(field(m, 2, "deps")?, "deps")?
            .iter()
            .map(|d| oref(d, "dep"))
            .collect::<Result<Vec<_>, _>>()?;
        if !deps.windows(2).all(|w| w[0] < w[1]) {
            return schema("deps must be sorted and unique");
        }
        if deps.iter().any(|d| d.is_zero()) {
            return schema("deps may not contain the self reference");
        }
        let extra = map(field(m, 9, "extra")?, "extra")?;
        if !extra.is_empty() {
            return schema("extra must be empty in format version 1");
        }
        Ok(Change {
            change_id,
            deps,
            author: oref(field(m, 3, "author")?, "author")?,
            hlc: Hlc::from_value(field(m, 4, "hlc")?)?,
            message: text(field(m, 5, "message")?, "message")?.to_owned(),
            tree_ops: array(field(m, 6, "tree_ops")?, "tree_ops")?
                .iter()
                .map(TreeOp::from_value)
                .collect::<Result<Vec<_>, _>>()?,
            edits: array(field(m, 7, "edits")?, "edits")?
                .iter()
                .map(Edit::from_value)
                .collect::<Result<Vec<_>, _>>()?,
            kind: ChangeKind::from_tag(uint(field(m, 8, "kind")?, "kind")?)?,
        })
    }
}

// ---------------------------------------------------------------- blob

/// File content as an ordered list of chunks (spec §13.2).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Blob {
    pub length: u64,
    pub chunks: Vec<ObjectRef>,
}

impl Blob {
    pub fn encode(&self) -> Vec<u8> {
        cbor::encode(&Value::map([
            (0, Value::Uint(FORMAT_VERSION)),
            (1, Value::Uint(self.length)),
            (2, Value::Array(self.chunks.iter().map(|c| Value::Bytes(c.0.to_vec())).collect())),
        ]))
    }
    pub fn hash(&self) -> ObjectRef {
        hash_object(ObjectType::Blob, &self.encode())
    }
    pub fn decode(bytes: &[u8]) -> Result<Blob, ObjectError> {
        let v = cbor::decode(bytes)?;
        let m = map(&v, "blob")?;
        check_version(m)?;
        Ok(Blob {
            length: uint(field(m, 1, "length")?, "length")?,
            chunks: array(field(m, 2, "chunks")?, "chunks")?
                .iter()
                .map(|c| oref(c, "chunk"))
                .collect::<Result<Vec<_>, _>>()?,
        })
    }
}

#[cfg(test)]
pub(crate) mod tests {
    use super::*;

    pub(crate) fn sample_change() -> Change {
        let n = NodeId([7; 16]);
        let dep = ObjectRef([1; 32]);
        let mut c = Change {
            change_id: ChangeId([9; 16]),
            deps: vec![ObjectRef([2; 32]), dep],
            author: ObjectRef([3; 32]),
            hlc: Hlc { wall_ms: 1_700_000_000_000, logical: 4 },
            message: "Add greeting".into(),
            tree_ops: vec![
                TreeOp::AddNode { node: n, kind: NodeKind::File, mode: Mode::TEXT, parent: NodeId::ROOT, name: "hello.txt".into() },
                TreeOp::SetMode { node: n, old: OpRef { change: ObjectRef::ZERO, index: 0 }, mode: Mode { exec: true, opaque: false } },
            ],
            edits: vec![
                Edit::Insert { node: n, after: AtomRef::Start, before: AtomRef::End, lines: vec![b"hello\n".to_vec(), b"world\n".to_vec()] },
                Edit::Delete { node: n, atoms: vec![AtomRange { change: dep, from: 0, to: 2 }] },
                Edit::Replace { node: n, old: None, new: Some(ObjectRef([5; 32])) },
            ],
            kind: ChangeKind::Normal,
        };
        c.normalize();
        c
    }

    #[test]
    fn change_round_trips_and_hash_is_stable() {
        let c = sample_change();
        let bytes = c.encode();
        let d = Change::decode(&bytes).unwrap();
        assert_eq!(c, d);
        assert_eq!(c.hash(), d.hash());
        assert_eq!(d.encode(), bytes);
        // Any semantic difference changes the hash.
        let mut e = c.clone();
        e.message.push('!');
        assert_ne!(e.hash(), c.hash());
    }

    #[test]
    fn decode_rejects_bad_changes() {
        let c = sample_change();
        let mut v = c.to_value();
        if let Value::Map(m) = &mut v {
            m.insert(0, Value::Uint(2));
        }
        assert!(matches!(Change::from_value(&v), Err(ObjectError::Schema(s)) if s.contains("version")));

        let mut v = c.to_value();
        if let Value::Map(m) = &mut v {
            m.insert(2, Value::Array(vec![Value::Bytes(vec![2; 32]), Value::Bytes(vec![1; 32])]));
        }
        assert!(matches!(Change::from_value(&v), Err(ObjectError::Schema(s)) if s.contains("sorted")));

        let mut v = c.to_value();
        if let Value::Map(m) = &mut v {
            m.insert(9, Value::map([(0, Value::Null)]));
        }
        assert!(matches!(Change::from_value(&v), Err(ObjectError::Schema(s)) if s.contains("extra")));
    }

    #[test]
    fn names_are_validated() {
        for bad in ["", ".", "..", "a/b", "a\0b"] {
            assert!(validate_name(bad).is_err(), "{bad:?}");
        }
        assert!(validate_name("Foo.c").is_ok());
        assert!(validate_name("...").is_ok());
    }

    #[test]
    fn mode_and_kind_tags() {
        for m in [Mode::TEXT, Mode::OPAQUE, Mode { exec: true, opaque: true }] {
            assert_eq!(Mode::from_bits(m.bits()).unwrap(), m);
        }
        assert!(Mode::from_bits(4).is_err());
        for k in [NodeKind::File, NodeKind::Dir, NodeKind::Symlink] {
            assert_eq!(NodeKind::from_tag(k.tag()).unwrap(), k);
        }
    }

    #[test]
    fn self_references_resolve() {
        let me = ObjectRef([8; 32]);
        assert_eq!(AtomRef::Atom { change: ObjectRef::ZERO, index: 3 }.resolve(me), AtomRef::Atom { change: me, index: 3 });
        assert_eq!(AtomRef::Start.resolve(me), AtomRef::Start);
        let other = ObjectRef([1; 32]);
        assert_eq!(OpRef { change: other, index: 1 }.resolve(me).change, other);
    }

    #[test]
    fn blob_round_trip() {
        let b = Blob { length: 10, chunks: vec![ObjectRef([1; 32]), ObjectRef([2; 32])] };
        assert_eq!(Blob::decode(&b.encode()).unwrap(), b);
    }
}
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