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view: add support for merging git ref targets
When there are two concurrent operations, we would resolve conflicting updates of git refs quite arbitrarily before this change. This change introduces a new `refs` module with a function for doing a 3-way merge of ref targets. For example, if both sides moved a ref forward but by different amounts, we pick the descendant-most target. If we can't resolve it, we leave it as a conflict. That's fine to do for git refs because they can be resolved by simply running `jj git refresh` to import refs again (the underlying git repo is the source of truth). As with the previous change, I'm doing this now because mostly because it is a good stepping stone towards branch support (issue libfuse#21). We'll soon use the same 3-way merging for updating the local branch definition (once we add that) when a branch changes in the git repo or on a remote.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,109 @@ | ||
| // Copyright 2021 Google LLC | ||
| // | ||
| // 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 crate::index::IndexRef; | ||
| use crate::op_store::RefTarget; | ||
| use crate::store::CommitId; | ||
|
|
||
| pub fn merge_ref_targets( | ||
| index: IndexRef, | ||
| left: Option<&RefTarget>, | ||
| base: Option<&RefTarget>, | ||
| right: Option<&RefTarget>, | ||
| ) -> Option<RefTarget> { | ||
| if left == base || left == right { | ||
| right.cloned() | ||
| } else if base == right { | ||
| left.cloned() | ||
| } else { | ||
| let mut adds = vec![]; | ||
| let mut removes = vec![]; | ||
| if let Some(left) = left { | ||
| adds.extend(left.adds()); | ||
| removes.extend(left.removes()); | ||
| } | ||
| if let Some(base) = base { | ||
| // Note that these are backwards (because the base is subtracted). | ||
| adds.extend(base.removes()); | ||
| removes.extend(base.adds()); | ||
| } | ||
| if let Some(right) = right { | ||
| adds.extend(right.adds()); | ||
| removes.extend(right.removes()); | ||
| } | ||
|
|
||
| while let Some((maybe_remove_index, add_index)) = | ||
| find_pair_to_remove(index, &adds, &removes) | ||
| { | ||
| if let Some(remove_index) = maybe_remove_index { | ||
| removes.remove(remove_index); | ||
| } | ||
| adds.remove(add_index); | ||
| } | ||
|
|
||
| if adds.is_empty() { | ||
| None | ||
| } else if adds.len() == 1 && removes.is_empty() { | ||
| Some(RefTarget::Normal(adds[0].clone())) | ||
| } else { | ||
| Some(RefTarget::Conflict { removes, adds }) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn find_pair_to_remove( | ||
| index: IndexRef, | ||
| adds: &[CommitId], | ||
| removes: &[CommitId], | ||
| ) -> Option<(Option<usize>, usize)> { | ||
| // Removes pairs of matching adds and removes. | ||
| for (add_index, add) in adds.iter().enumerate() { | ||
| for (remove_index, remove) in removes.iter().enumerate() { | ||
| if add == remove { | ||
| return Some((Some(remove_index), add_index)); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // If a "remove" is an ancestor of two different "adds" and one of the | ||
| // "adds" is an ancestor of the other, then pick the descendant. | ||
| for (add_index1, add1) in adds.iter().enumerate() { | ||
| for (add_index2, add2) in adds.iter().enumerate().skip(add_index1 + 1) { | ||
| let first_add_is_ancestor; | ||
| if add1 == add2 || index.is_ancestor(add1, add2) { | ||
| first_add_is_ancestor = true; | ||
| } else if index.is_ancestor(add2, add1) { | ||
| first_add_is_ancestor = false; | ||
| } else { | ||
| continue; | ||
| } | ||
| if removes.is_empty() { | ||
| if first_add_is_ancestor { | ||
| return Some((None, add_index1)); | ||
| } else { | ||
| return Some((None, add_index2)); | ||
| } | ||
| } | ||
| for (remove_index, remove) in removes.iter().enumerate() { | ||
| if first_add_is_ancestor && index.is_ancestor(remove, add1) { | ||
| return Some((Some(remove_index), add_index1)); | ||
| } else if !first_add_is_ancestor && index.is_ancestor(remove, add2) { | ||
| return Some((Some(remove_index), add_index2)); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| None | ||
| } |
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