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Parallelize revisions by making them siblings Running `jj parallelize 1::2` will transform the history like this: ```text 3 | 3 2 / \ | -> 1 2 1 \ / | 0 0 ``` Each of the target revisions is rebased onto the parents of the root(s) of the target revset (not to be confused with the repo root). The children of the head(s) of the target revset are rebased onto the target revisions. The target revset is the union of the REVISIONS arguments. The target revset being parallelized must satisfy several conditions, otherwise the command will fail. 1. The heads of the target revset must not have different children. 2. The roots of the target revset must not have different parents. 3. The parents of all target revisions except the roots must also be parallelized. This means that the target revisions must be connected.
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| // Copyright 2024 The Jujutsu Authors | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // https://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| use std::collections::HashSet; | ||
| use std::io::Write; | ||
| use std::rc::Rc; | ||
|
|
||
| use indexmap::IndexSet; | ||
| use itertools::Itertools; | ||
| use jj_lib::backend::CommitId; | ||
| use jj_lib::commit::{Commit, CommitIteratorExt}; | ||
| use jj_lib::repo::Repo; | ||
| use jj_lib::revset::{RevsetExpression, RevsetIteratorExt}; | ||
| use tracing::instrument; | ||
|
|
||
| use crate::cli_util::{CommandHelper, RevisionArg}; | ||
| use crate::command_error::{user_error, CommandError}; | ||
| use crate::commands::rebase::rebase_descendants; | ||
| use crate::ui::Ui; | ||
|
|
||
| /// Parallelize revisions by making them siblings | ||
| /// | ||
| /// Running `jj parallelize 1::2` will transform the history like this: | ||
| /// ```text | ||
| /// 3 | ||
| /// | 3 | ||
| /// 2 / \ | ||
| /// | -> 1 2 | ||
| /// 1 \ / | ||
| /// | 0 | ||
| /// 0 | ||
| /// ``` | ||
| /// | ||
| /// Each of the target revisions is rebased onto the parents of the root(s) of | ||
| /// the target revset (not to be confused with the repo root). The children of | ||
| /// the head(s) of the target revset are rebased onto the target revisions. | ||
| /// | ||
| /// The target revset is the union of the REVISIONS arguments and must satisfy | ||
| /// several conditions, otherwise the command will fail. | ||
| /// | ||
| /// 1. The heads of the target revset must have either the same children as the | ||
| /// other heads or none. | ||
| /// 2. The roots of the target revset have the same parents. | ||
| /// 3. The parents of all target revisions except the roots must also be | ||
| /// parallelized. This means that the target revisions must be connected. | ||
| #[derive(clap::Args, Clone, Debug)] | ||
| #[command(verbatim_doc_comment)] | ||
| pub(crate) struct ParallelizeArgs { | ||
| /// Revisions to parallelize | ||
| revisions: Vec<RevisionArg>, | ||
| } | ||
|
|
||
| #[instrument(skip_all)] | ||
| pub(crate) fn cmd_parallelize( | ||
| ui: &mut Ui, | ||
| command: &CommandHelper, | ||
| args: &ParallelizeArgs, | ||
| ) -> Result<(), CommandError> { | ||
| let mut workspace_command = command.workspace_helper(ui)?; | ||
| // The target commits are the commits being parallelized. They are ordered | ||
| // here with parents before children. | ||
| let target_commits: Vec<Commit> = workspace_command | ||
| .parse_union_revsets(&args.revisions)? | ||
| .evaluate_to_commits()? | ||
| .try_collect()?; | ||
| if target_commits.len() < 2 { | ||
| writeln!(ui.status(), "Nothing changed.")?; | ||
| return Ok(()); | ||
| } | ||
| workspace_command.check_rewritable(target_commits.iter().ids())?; | ||
|
|
||
| let mut tx = workspace_command.start_transaction(); | ||
| let target_revset = | ||
| RevsetExpression::commits(target_commits.iter().ids().cloned().collect_vec()); | ||
| let new_parents = | ||
| check_preconditions_and_get_new_parents(&target_revset, &target_commits, tx.repo())?; | ||
|
|
||
| // Rebase the non-target children of each target commit onto its new | ||
| // parents. A child which had a target commit as an ancestor before | ||
| // parallelize ran will have the target commit as a parent afterward. | ||
| for target_commit in target_commits.iter() { | ||
| // Children of the target commit, excluding other target commits. | ||
| let children: Vec<Commit> = RevsetExpression::commit(target_commit.id().clone()) | ||
| .children() | ||
| .minus(&target_revset) | ||
| .evaluate_programmatic(tx.repo())? | ||
| .iter() | ||
| .commits(tx.repo().store()) | ||
| .try_collect()?; | ||
| // These parents are shared by all children of the target commit and | ||
| // include the target commit itself plus any of its ancestors which are | ||
| // being parallelized. | ||
| let common_parents: IndexSet<Commit> = RevsetExpression::commit(target_commit.id().clone()) | ||
| .ancestors() | ||
| .intersection(&target_revset) | ||
| .evaluate_programmatic(tx.repo())? | ||
| .iter() | ||
| .commits(tx.repo().store()) | ||
| .try_collect()?; | ||
| for child in children { | ||
| let mut new_parents = common_parents.clone(); | ||
| new_parents.extend(child.parents().into_iter()); | ||
| rebase_descendants( | ||
| &mut tx, | ||
| command.settings(), | ||
| &new_parents.into_iter().collect_vec(), | ||
| &[child], | ||
| Default::default(), | ||
| )?; | ||
| } | ||
| } | ||
|
|
||
| // Rebase the target commits onto the parents of the root commit. | ||
| // We already checked that the roots have the same parents, so we can just | ||
| // use the first one. | ||
| let target_commits = target_commits | ||
| .into_iter() | ||
| // We need to reverse the iterator so that when we rebase the target | ||
| // commits they will appear in the same relative order in `jj log` that | ||
| // they were in before being parallelized. After reversing, the commits | ||
| // are ordered with children before parents. | ||
| .rev() | ||
| .collect_vec(); | ||
| rebase_descendants( | ||
| &mut tx, | ||
| command.settings(), | ||
| &new_parents, | ||
| &target_commits, | ||
| Default::default(), | ||
| )?; | ||
|
|
||
| tx.finish(ui, format!("parallelize {} commits", target_commits.len())) | ||
| } | ||
|
|
||
| /// Returns the new parents of the parallelized commits or an error if any of | ||
| /// the following preconditions are not met: | ||
| /// | ||
| /// 1. If the heads of the target revset must not have different children. | ||
| /// 2. The roots of the target revset must not have different parents. | ||
| /// 3. The parents of all target revisions except the roots must also be | ||
| /// parallelized. This means that the target revisions must be connected. | ||
| /// | ||
| /// The `target_revset` must evaluate to the commits in `target_commits` when | ||
| /// the provided `repo` is used. | ||
| fn check_preconditions_and_get_new_parents( | ||
| target_revset: &Rc<RevsetExpression>, | ||
| target_commits: &[Commit], | ||
| repo: &dyn Repo, | ||
| ) -> Result<Vec<Commit>, CommandError> { | ||
| check_target_heads(target_revset, repo)?; | ||
| let target_roots = check_target_roots(target_revset, repo)?; | ||
| check_target_commits_are_connected(&target_roots, target_commits)?; | ||
|
|
||
| // We already verified that the roots have the same parents, so we can just | ||
| // use the first root. | ||
| Ok(target_roots[0].parents()) | ||
| } | ||
|
|
||
| /// Returns an error if the heads of the target revset have children which are | ||
| /// different. | ||
| fn check_target_heads( | ||
| target_revset: &Rc<RevsetExpression>, | ||
| repo: &dyn Repo, | ||
| ) -> Result<(), CommandError> { | ||
| let target_heads = target_revset | ||
| .heads() | ||
| .evaluate_programmatic(repo)? | ||
| .iter() | ||
| .sorted() | ||
| .collect_vec(); | ||
| if target_heads.len() == 1 { | ||
| return Ok(()); | ||
| } | ||
| let all_children: Vec<Commit> = target_revset | ||
| .heads() | ||
| .children() | ||
| .evaluate_programmatic(repo)? | ||
| .iter() | ||
| .commits(repo.store()) | ||
| .try_collect()?; | ||
| // Every child must have every target head as a parent, otherwise it means | ||
| // that the target heads have different children. | ||
| for child in all_children { | ||
| let parents = child.parent_ids().iter().sorted(); | ||
| if !parents.eq(target_heads.iter()) { | ||
| return Err(user_error( | ||
| "All heads of the target revisions must have the same children.", | ||
| )); | ||
| } | ||
| } | ||
| Ok(()) | ||
| } | ||
|
|
||
| /// Returns the roots of the target revset or an error if their parents are | ||
| /// different. | ||
| fn check_target_roots( | ||
| target_revset: &Rc<RevsetExpression>, | ||
| repo: &dyn Repo, | ||
| ) -> Result<Vec<Commit>, CommandError> { | ||
| let target_roots: Vec<Commit> = target_revset | ||
| .roots() | ||
| .evaluate_programmatic(repo)? | ||
| .iter() | ||
| .commits(repo.store()) | ||
| .try_collect()?; | ||
| let expected_parents = target_roots[0].parent_ids().iter().sorted().collect_vec(); | ||
| for root in target_roots[1..].iter() { | ||
| let root_parents = root.parent_ids().iter().sorted(); | ||
| if !root_parents.eq(expected_parents.iter().copied()) { | ||
| return Err(user_error( | ||
| "All roots of the target revisions must have the same parents.", | ||
| )); | ||
| } | ||
| } | ||
| Ok(target_roots) | ||
| } | ||
|
|
||
| /// The target commits must be connected. The parents of every target commit | ||
| /// except the root commit must also be target commits. Returns an error if this | ||
| /// requirement is not met. | ||
| fn check_target_commits_are_connected( | ||
| target_roots: &[Commit], | ||
| target_commits: &[Commit], | ||
| ) -> Result<(), CommandError> { | ||
| let target_commit_ids: HashSet<CommitId> = target_commits.iter().ids().cloned().collect(); | ||
| for target_commit in target_commits.iter() { | ||
| if target_roots.iter().ids().contains(target_commit.id()) { | ||
| continue; | ||
| } | ||
| for parent in target_commit.parent_ids() { | ||
| if !target_commit_ids.contains(parent) { | ||
| // We check this condition to return a more useful error to the user. | ||
| if target_commit.parent_ids().len() == 1 { | ||
| return Err(user_error( | ||
| "Cannot parallelize since the target revisions are not connected.", | ||
| )); | ||
| } | ||
| return Err(user_error( | ||
| "Only the roots of the target revset are allowed to have parents which are \ | ||
| not being parallelized.", | ||
| )); | ||
| } | ||
| } | ||
| } | ||
| Ok(()) | ||
| } |
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