index: extract as_composite() to trait method

The revset engine will accept abstract AsCompositeIndex type, and the
evaluated revset can be 'static if the index is behind Arc<T>.

cli/src/commands/debug.rs

@@ -18,7 +18,7 @@ use std::io::Write as _;
 
 use clap::Subcommand;
 use jj_lib::backend::ObjectId;
-use jj_lib::default_index::{DefaultIndexStore, DefaultReadonlyIndex};
+use jj_lib::default_index::{AsCompositeIndex as _, DefaultIndexStore, DefaultReadonlyIndex};
 use jj_lib::local_working_copy::LocalWorkingCopy;
 use jj_lib::revset;
 use jj_lib::working_copy::WorkingCopy;

lib/src/default_index/composite.rs

@@ -63,6 +63,26 @@ pub(super) trait IndexSegment: Send + Sync {
     fn segment_entry_by_pos(&self, pos: IndexPosition, local_pos: u32) -> IndexEntry;
 }
 
+/// Abstraction over owned and borrowed types that can be cheaply converted to
+/// a `CompositeIndex` reference.
+pub trait AsCompositeIndex {
+    /// Returns reference wrapper that provides global access to this index.
+    fn as_composite(&self) -> CompositeIndex<'_>;
+}
+
+impl<T: AsCompositeIndex + ?Sized> AsCompositeIndex for &T {
+    fn as_composite(&self) -> CompositeIndex<'_> {
+        <T as AsCompositeIndex>::as_composite(self)
+    }
+}
+
+impl<T: AsCompositeIndex + ?Sized> AsCompositeIndex for &mut T {
+    fn as_composite(&self) -> CompositeIndex<'_> {
+        <T as AsCompositeIndex>::as_composite(self)
+    }
+}
+
+/// Reference wrapper that provides global access to nested index segments.
 #[derive(Clone, Copy)]
 pub struct CompositeIndex<'a>(&'a dyn IndexSegment);
 
@@ -288,6 +308,12 @@ impl<'a> CompositeIndex<'a> {
     }
 }
 
+impl AsCompositeIndex for CompositeIndex<'_> {
+    fn as_composite(&self) -> CompositeIndex<'_> {
+        *self
+    }
+}
+
 impl Index for CompositeIndex<'_> {
     /// Suppose the given `commit_id` exists, returns the minimum prefix length
     /// to disambiguate it. The length to be returned is a number of hexadecimal

lib/src/default_index/mod.rs

@@ -21,7 +21,7 @@ mod readonly;
 mod rev_walk;
 mod store;
 
-pub use self::composite::{CompositeIndex, IndexLevelStats, IndexStats};
+pub use self::composite::{AsCompositeIndex, CompositeIndex, IndexLevelStats, IndexStats};
 pub use self::entry::{IndexEntry, IndexPosition};
 pub use self::mutable::DefaultMutableIndex;
 pub use self::readonly::DefaultReadonlyIndex;

lib/src/default_index/mutable.rs

@@ -30,7 +30,7 @@ use itertools::Itertools;
 use smallvec::SmallVec;
 use tempfile::NamedTempFile;
 
-use super::composite::{CompositeIndex, IndexSegment};
+use super::composite::{AsCompositeIndex, CompositeIndex, IndexSegment};
 use super::entry::{IndexEntry, IndexPosition, SmallIndexPositionsVec};
 use super::readonly::{DefaultReadonlyIndex, ReadonlyIndexSegment};
 use super::store::IndexLoadError;
@@ -403,10 +403,6 @@ impl DefaultMutableIndex {
         DefaultMutableIndex(mutable_segment)
     }
 
-    pub fn as_composite(&self) -> CompositeIndex {
-        self.0.as_composite()
-    }
-
     #[cfg(test)]
     pub(crate) fn add_commit_data(
         &mut self,
@@ -422,6 +418,12 @@ impl DefaultMutableIndex {
     }
 }
 
+impl AsCompositeIndex for DefaultMutableIndex {
+    fn as_composite(&self) -> CompositeIndex<'_> {
+        self.0.as_composite()
+    }
+}
+
 impl Index for DefaultMutableIndex {
     fn shortest_unique_commit_id_prefix_len(&self, commit_id: &CommitId) -> usize {
         self.as_composite()

lib/src/default_index/readonly.rs

@@ -25,7 +25,7 @@ use std::sync::Arc;
 use byteorder::{LittleEndian, ReadBytesExt};
 use smallvec::SmallVec;
 
-use super::composite::{CompositeIndex, IndexSegment};
+use super::composite::{AsCompositeIndex, CompositeIndex, IndexSegment};
 use super::entry::{IndexEntry, IndexPosition, SmallIndexPositionsVec};
 use super::mutable::DefaultMutableIndex;
 use super::store::IndexLoadError;
@@ -384,8 +384,10 @@ impl DefaultReadonlyIndex {
     pub(super) fn as_segment(&self) -> &Arc<ReadonlyIndexSegment> {
         &self.0
     }
+}
 
-    pub fn as_composite(&self) -> CompositeIndex {
+impl AsCompositeIndex for DefaultReadonlyIndex {
+    fn as_composite(&self) -> CompositeIndex<'_> {
         self.0.as_composite()
     }
 }

lib/src/default_revset_engine.rs

@@ -978,7 +978,7 @@ fn has_diff_from_parent(
 mod tests {
     use super::*;
     use crate::backend::{ChangeId, CommitId, ObjectId};
-    use crate::default_index::DefaultMutableIndex;
+    use crate::default_index::{AsCompositeIndex as _, DefaultMutableIndex};
 
     /// Generator of unique 16-byte ChangeId excluding root id
     fn change_id_generator() -> impl FnMut() -> ChangeId {

lib/tests/test_default_revset_graph_iterator.rs

@@ -14,7 +14,7 @@
 
 use itertools::Itertools;
 use jj_lib::commit::Commit;
-use jj_lib::default_index::DefaultReadonlyIndex;
+use jj_lib::default_index::{AsCompositeIndex as _, DefaultReadonlyIndex};
 use jj_lib::default_revset_engine::{evaluate, RevsetImpl};
 use jj_lib::repo::{ReadonlyRepo, Repo as _};
 use jj_lib::revset::ResolvedExpression;

lib/tests/test_index.rs

@@ -18,7 +18,7 @@ use jj_lib::backend::CommitId;
 use jj_lib::commit::Commit;
 use jj_lib::commit_builder::CommitBuilder;
 use jj_lib::default_index::{
-    CompositeIndex, DefaultMutableIndex, DefaultReadonlyIndex, IndexPosition,
+    AsCompositeIndex as _, CompositeIndex, DefaultMutableIndex, DefaultReadonlyIndex, IndexPosition,
 };
 use jj_lib::index::Index as _;
 use jj_lib::repo::{MutableRepo, ReadonlyRepo, Repo};