jj_lib/
op_walk.rs

1// Copyright 2020-2023 The Jujutsu Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// https://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15//! Utility for operation id resolution and traversal.
16
17use std::cmp::Ordering;
18use std::collections::HashMap;
19use std::collections::HashSet;
20use std::slice;
21use std::sync::Arc;
22
23use itertools::Itertools as _;
24use thiserror::Error;
25
26use crate::dag_walk;
27use crate::object_id::HexPrefix;
28use crate::object_id::PrefixResolution;
29use crate::op_heads_store;
30use crate::op_heads_store::OpHeadResolutionError;
31use crate::op_heads_store::OpHeadsStore;
32use crate::op_heads_store::OpHeadsStoreError;
33use crate::op_store::OpStore;
34use crate::op_store::OpStoreError;
35use crate::op_store::OpStoreResult;
36use crate::op_store::OperationId;
37use crate::operation::Operation;
38use crate::repo::ReadonlyRepo;
39use crate::repo::Repo as _;
40use crate::repo::RepoLoader;
41
42/// Error that may occur during evaluation of operation set expression.
43#[derive(Debug, Error)]
44pub enum OpsetEvaluationError {
45    /// Failed to resolve operation set expression.
46    #[error(transparent)]
47    OpsetResolution(#[from] OpsetResolutionError),
48    /// Failed to read op heads.
49    #[error(transparent)]
50    OpHeadsStore(#[from] OpHeadsStoreError),
51    /// Failed to resolve the current operation heads.
52    #[error(transparent)]
53    OpHeadResolution(#[from] OpHeadResolutionError),
54    /// Failed to access operation object.
55    #[error(transparent)]
56    OpStore(#[from] OpStoreError),
57}
58
59/// Error that may occur during parsing and resolution of operation set
60/// expression.
61#[derive(Debug, Error)]
62pub enum OpsetResolutionError {
63    // TODO: Maybe empty/multiple operations should be allowed, and rejected by
64    // caller as needed.
65    /// Expression resolved to multiple operations.
66    #[error(r#"The "{expr}" expression resolved to more than one operation"#)]
67    MultipleOperations {
68        /// Source expression.
69        expr: String,
70        /// Matched operation ids.
71        candidates: Vec<OperationId>,
72    },
73    /// Expression resolved to no operations.
74    #[error(r#"The "{0}" expression resolved to no operations"#)]
75    EmptyOperations(String),
76    /// Invalid symbol as an operation ID.
77    #[error(r#"Operation ID "{0}" is not a valid hexadecimal prefix"#)]
78    InvalidIdPrefix(String),
79    /// Operation ID not found.
80    #[error(r#"No operation ID matching "{0}""#)]
81    NoSuchOperation(String),
82    /// Operation ID prefix matches multiple operations.
83    #[error(r#"Operation ID prefix "{0}" is ambiguous"#)]
84    AmbiguousIdPrefix(String),
85}
86
87/// Resolves operation set expression without loading a repo.
88pub fn resolve_op_for_load(
89    repo_loader: &RepoLoader,
90    op_str: &str,
91) -> Result<Operation, OpsetEvaluationError> {
92    let op_store = repo_loader.op_store();
93    let op_heads_store = repo_loader.op_heads_store().as_ref();
94    let get_current_op = || {
95        op_heads_store::resolve_op_heads(op_heads_store, op_store, |op_heads| {
96            Err(OpsetResolutionError::MultipleOperations {
97                expr: "@".to_owned(),
98                candidates: op_heads.iter().map(|op| op.id().clone()).collect(),
99            }
100            .into())
101        })
102    };
103    let get_head_ops = || get_current_head_ops(op_store, op_heads_store);
104    resolve_single_op(op_store, get_current_op, get_head_ops, op_str)
105}
106
107/// Resolves operation set expression against the loaded repo.
108///
109/// The "@" symbol will be resolved to the operation the repo was loaded at.
110pub fn resolve_op_with_repo(
111    repo: &ReadonlyRepo,
112    op_str: &str,
113) -> Result<Operation, OpsetEvaluationError> {
114    resolve_op_at(repo.op_store(), slice::from_ref(repo.operation()), op_str)
115}
116
117/// Resolves operation set expression at the given head operations.
118pub fn resolve_op_at(
119    op_store: &Arc<dyn OpStore>,
120    head_ops: &[Operation],
121    op_str: &str,
122) -> Result<Operation, OpsetEvaluationError> {
123    let get_current_op = || match head_ops {
124        [head_op] => Ok(head_op.clone()),
125        [] => Err(OpsetResolutionError::EmptyOperations("@".to_owned()).into()),
126        _ => Err(OpsetResolutionError::MultipleOperations {
127            expr: "@".to_owned(),
128            candidates: head_ops.iter().map(|op| op.id().clone()).collect(),
129        }
130        .into()),
131    };
132    let get_head_ops = || Ok(head_ops.to_vec());
133    resolve_single_op(op_store, get_current_op, get_head_ops, op_str)
134}
135
136/// Resolves operation set expression with the given "@" symbol resolution
137/// callbacks.
138fn resolve_single_op(
139    op_store: &Arc<dyn OpStore>,
140    get_current_op: impl FnOnce() -> Result<Operation, OpsetEvaluationError>,
141    get_head_ops: impl FnOnce() -> Result<Vec<Operation>, OpsetEvaluationError>,
142    op_str: &str,
143) -> Result<Operation, OpsetEvaluationError> {
144    let op_symbol = op_str.trim_end_matches(['-', '+']);
145    let op_postfix = &op_str[op_symbol.len()..];
146    let head_ops = op_postfix.contains('+').then(get_head_ops).transpose()?;
147    let mut operation = match op_symbol {
148        "@" => get_current_op(),
149        s => resolve_single_op_from_store(op_store, s),
150    }?;
151    for c in op_postfix.chars() {
152        let mut neighbor_ops = match c {
153            '-' => operation.parents().try_collect()?,
154            '+' => find_child_ops(head_ops.as_ref().unwrap(), operation.id())?,
155            _ => unreachable!(),
156        };
157        operation = match neighbor_ops.len() {
158            0 => Err(OpsetResolutionError::EmptyOperations(op_str.to_owned()))?,
159            1 => neighbor_ops.pop().unwrap(),
160            _ => Err(OpsetResolutionError::MultipleOperations {
161                expr: op_str.to_owned(),
162                candidates: neighbor_ops.iter().map(|op| op.id().clone()).collect(),
163            })?,
164        };
165    }
166    Ok(operation)
167}
168
169fn resolve_single_op_from_store(
170    op_store: &Arc<dyn OpStore>,
171    op_str: &str,
172) -> Result<Operation, OpsetEvaluationError> {
173    if op_str.is_empty() {
174        return Err(OpsetResolutionError::InvalidIdPrefix(op_str.to_owned()).into());
175    }
176    let prefix = HexPrefix::new(op_str)
177        .ok_or_else(|| OpsetResolutionError::InvalidIdPrefix(op_str.to_owned()))?;
178    match op_store.resolve_operation_id_prefix(&prefix)? {
179        PrefixResolution::NoMatch => {
180            Err(OpsetResolutionError::NoSuchOperation(op_str.to_owned()).into())
181        }
182        PrefixResolution::SingleMatch(op_id) => {
183            let data = op_store.read_operation(&op_id)?;
184            Ok(Operation::new(op_store.clone(), op_id, data))
185        }
186        PrefixResolution::AmbiguousMatch => {
187            Err(OpsetResolutionError::AmbiguousIdPrefix(op_str.to_owned()).into())
188        }
189    }
190}
191
192/// Loads the current head operations. The returned operations may contain
193/// redundant ones which are ancestors of the other heads.
194pub fn get_current_head_ops(
195    op_store: &Arc<dyn OpStore>,
196    op_heads_store: &dyn OpHeadsStore,
197) -> Result<Vec<Operation>, OpsetEvaluationError> {
198    let mut head_ops: Vec<_> = op_heads_store
199        .get_op_heads()?
200        .into_iter()
201        .map(|id| -> OpStoreResult<Operation> {
202            let data = op_store.read_operation(&id)?;
203            Ok(Operation::new(op_store.clone(), id, data))
204        })
205        .try_collect()?;
206    // To stabilize output, sort in the same order as resolve_op_heads()
207    head_ops.sort_by_key(|op| op.metadata().end_time.timestamp);
208    Ok(head_ops)
209}
210
211/// Looks up children of the `root_op_id` by traversing from the `head_ops`.
212///
213/// This will be slow if the `root_op_id` is far away (or unreachable) from the
214/// `head_ops`.
215fn find_child_ops(
216    head_ops: &[Operation],
217    root_op_id: &OperationId,
218) -> OpStoreResult<Vec<Operation>> {
219    walk_ancestors(head_ops)
220        .take_while(|res| res.as_ref().map_or(true, |op| op.id() != root_op_id))
221        .filter_ok(|op| op.parent_ids().iter().any(|id| id == root_op_id))
222        .try_collect()
223}
224
225#[derive(Clone, Debug, Eq, Hash, PartialEq)]
226struct OperationByEndTime(Operation);
227
228impl Ord for OperationByEndTime {
229    fn cmp(&self, other: &Self) -> Ordering {
230        let self_end_time = &self.0.metadata().end_time;
231        let other_end_time = &other.0.metadata().end_time;
232        self_end_time
233            .cmp(other_end_time)
234            .then_with(|| self.0.cmp(&other.0)) // to comply with Eq
235    }
236}
237
238impl PartialOrd for OperationByEndTime {
239    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
240        Some(self.cmp(other))
241    }
242}
243
244/// Walks `head_ops` and their ancestors in reverse topological order.
245pub fn walk_ancestors(
246    head_ops: &[Operation],
247) -> impl Iterator<Item = OpStoreResult<Operation>> + use<> {
248    // Emit the latest head first to stabilize the order.
249    let mut head_ops = head_ops
250        .iter()
251        .cloned()
252        .map(OperationByEndTime)
253        .collect_vec();
254    head_ops.sort_unstable_by(|op1, op2| op1.cmp(op2).reverse());
255    // Lazily load operations based on timestamp-based heuristic. This works so long
256    // as the operation history is mostly linear.
257    dag_walk::topo_order_reverse_lazy_ok(
258        head_ops.into_iter().map(Ok),
259        |OperationByEndTime(op)| op.id().clone(),
260        |OperationByEndTime(op)| op.parents().map_ok(OperationByEndTime).collect_vec(),
261    )
262    .map_ok(|OperationByEndTime(op)| op)
263}
264
265/// Stats about `reparent_range()`.
266#[derive(Clone, Debug, Eq, PartialEq)]
267pub struct ReparentStats {
268    /// New head operation ids in order of the old `head_ops`.
269    pub new_head_ids: Vec<OperationId>,
270    /// The number of rewritten operations.
271    pub rewritten_count: usize,
272    /// The number of ancestor operations that become unreachable from the
273    /// rewritten heads.
274    pub unreachable_count: usize,
275}
276
277/// Reparents the operation range `root_ops..head_ops` onto the `dest_op`.
278///
279/// Returns the new head operation ids as well as some stats. If the old
280/// operation heads are remapped to the new heads, the operations within the
281/// range `dest_op..root_ops` become unreachable.
282///
283/// If the source operation range `root_ops..head_ops` was empty, the
284/// `new_head_ids` will be `[dest_op.id()]`, meaning the `dest_op` is the head.
285// TODO: Find better place to host this function. It might be an OpStore method.
286pub fn reparent_range(
287    op_store: &dyn OpStore,
288    root_ops: &[Operation],
289    head_ops: &[Operation],
290    dest_op: &Operation,
291) -> OpStoreResult<ReparentStats> {
292    // Calculate ::root_ops to exclude them from the source range and count the
293    // number of operations that become unreachable.
294    let mut unwanted_ids: HashSet<_> = walk_ancestors(root_ops)
295        .map_ok(|op| op.id().clone())
296        .try_collect()?;
297    let ops_to_reparent: Vec<_> = walk_ancestors(head_ops)
298        .filter_ok(|op| !unwanted_ids.contains(op.id()))
299        .try_collect()?;
300    for op in walk_ancestors(slice::from_ref(dest_op)) {
301        unwanted_ids.remove(op?.id());
302    }
303    let unreachable_ids = unwanted_ids;
304
305    assert!(
306        ops_to_reparent
307            .last()
308            .is_none_or(|op| op.id() != op_store.root_operation_id()),
309        "root operation cannot be rewritten"
310    );
311    let mut rewritten_ids = HashMap::new();
312    for old_op in ops_to_reparent.into_iter().rev() {
313        let mut data = old_op.store_operation().clone();
314        let mut dest_once = Some(dest_op.id());
315        data.parents = data
316            .parents
317            .iter()
318            .filter_map(|id| rewritten_ids.get(id).or_else(|| dest_once.take()))
319            .cloned()
320            .collect();
321        let new_id = op_store.write_operation(&data)?;
322        rewritten_ids.insert(old_op.id().clone(), new_id);
323    }
324
325    let mut dest_once = Some(dest_op.id());
326    let new_head_ids = head_ops
327        .iter()
328        .filter_map(|op| rewritten_ids.get(op.id()).or_else(|| dest_once.take()))
329        .cloned()
330        .collect();
331    Ok(ReparentStats {
332        new_head_ids,
333        rewritten_count: rewritten_ids.len(),
334        unreachable_count: unreachable_ids.len(),
335    })
336}
jj_lib/op_walk.rs

jj_lib/
op_walk.rs
