feat: add Repository::merge_base_octopus()

gix/src/repository/merge.rs

@@ -233,6 +233,8 @@ impl Repository {
     ///
     /// Note that most of `options` are overwritten to match the requirements of a merge-base merge, but they can be useful
     /// to control the diff algorithm or rewrite tracking, for example.
+    ///
+    /// This method is useful in conjunction with [`Self::merge_trees()`], as the ancestor tree can be produced here.
     // TODO: test
     pub fn virtual_merge_base(
         &self,

gix/src/repository/mod.rs

@@ -171,7 +171,7 @@ pub mod virtual_merge_base_with_graph {
     #[derive(Debug, thiserror::Error)]
     #[allow(missing_docs)]
     pub enum Error {
-        #[error("Not commit was provided as merge-base")]
+        #[error("No commit was provided as merge-base")]
         MissingCommit,
         #[error(transparent)]
         MergeResourceCache(#[from] super::merge_resource_cache::Error),
@@ -186,6 +186,36 @@ pub mod virtual_merge_base_with_graph {
     }
 }
 
+///
+#[cfg(feature = "revision")]
+pub mod merge_base_octopus_with_graph {
+    /// The error returned by [Repository::merge_base_octopus_with_graph()](crate::Repository::merge_base_octopus_with_graph()).
+    #[derive(Debug, thiserror::Error)]
+    #[allow(missing_docs)]
+    pub enum Error {
+        #[error("No commit was provided")]
+        MissingCommit,
+        #[error("No merge base was found between the given commits")]
+        NoMergeBase,
+        #[error(transparent)]
+        MergeBase(#[from] gix_revision::merge_base::Error),
+    }
+}
+
+///
+#[cfg(feature = "revision")]
+pub mod merge_base_octopus {
+    /// The error returned by [Repository::merge_base_octopus()](crate::Repository::merge_base_octopus()).
+    #[derive(Debug, thiserror::Error)]
+    #[allow(missing_docs)]
+    pub enum Error {
+        #[error(transparent)]
+        OpenCache(#[from] crate::repository::commit_graph_if_enabled::Error),
+        #[error(transparent)]
+        MergeBaseOctopus(#[from] super::merge_base_octopus_with_graph::Error),
+    }
+}
+
 ///
 #[cfg(feature = "merge")]
 pub mod tree_merge_options {

gix/src/repository/revision.rs

@@ -1,3 +1,5 @@
+use crate::prelude::ObjectIdExt;
+use crate::repository::{merge_base_octopus, merge_base_octopus_with_graph};
 use crate::revision;
 #[cfg(feature = "revision")]
 use crate::{bstr::BStr, Id};
@@ -104,6 +106,38 @@ impl crate::Repository {
             .collect())
     }
 
+    /// Return the best merge-base among all `commits`, or fail if `commits` yields no commit or no merge-base was found.
+    ///
+    /// Use `graph` to speed up repeated calls.
+    #[cfg(feature = "revision")]
+    pub fn merge_base_octopus_with_graph(
+        &self,
+        commits: impl IntoIterator<Item = impl Into<gix_hash::ObjectId>>,
+        graph: &mut gix_revwalk::Graph<'_, '_, gix_revwalk::graph::Commit<gix_revision::merge_base::Flags>>,
+    ) -> Result<Id<'_>, merge_base_octopus_with_graph::Error> {
+        let commits: Vec<_> = commits.into_iter().map(Into::into).collect();
+        let first = commits
+            .first()
+            .copied()
+            .ok_or(merge_base_octopus_with_graph::Error::MissingCommit)?;
+        gix_revision::merge_base::octopus(first, &commits[1..], graph)?
+            .ok_or(merge_base_octopus_with_graph::Error::NoMergeBase)
+            .map(|id| id.attach(self))
+    }
+
+    /// Return the best merge-base among all `commits`, or fail if `commits` yields no commit or no merge-base was found.
+    ///
+    /// For repeated calls, prefer [`Self::merge_base_octopus_with_graph()`] for cache-reuse.
+    #[cfg(feature = "revision")]
+    pub fn merge_base_octopus(
+        &self,
+        commits: impl IntoIterator<Item = impl Into<gix_hash::ObjectId>>,
+    ) -> Result<Id<'_>, merge_base_octopus::Error> {
+        let cache = self.commit_graph_if_enabled()?;
+        let mut graph = self.revision_graph(cache.as_ref());
+        Ok(self.merge_base_octopus_with_graph(commits, &mut graph)?)
+    }
+
     /// Create the baseline for a revision walk by initializing it with the `tips` to start iterating on.
     ///
     /// It can be configured further before starting the actual walk.