index: add type alias for "dyn IndexSegment" to clarify it's 'static

This helps to migrate CompositeIndex<'_> wrapper to &CompositeIndex. If
the wrapped reference had a lifetimed field, it couldn't be represented as
a trivial reference type.

lib/src/default_index/composite.rs

@@ -76,6 +76,8 @@ pub(super) trait IndexSegment: Send + Sync {
     fn parent_positions(&self, local_pos: LocalPosition) -> SmallIndexPositionsVec;
 }
 
+pub(super) type DynIndexSegment = dyn IndexSegment;
+
 /// Abstraction over owned and borrowed types that can be cheaply converted to
 /// a `CompositeIndex` reference.
 pub trait AsCompositeIndex {
@@ -97,10 +99,10 @@ impl<T: AsCompositeIndex + ?Sized> AsCompositeIndex for &mut T {
 
 /// Reference wrapper that provides global access to nested index segments.
 #[derive(Clone, Copy)]
-pub struct CompositeIndex<'a>(&'a dyn IndexSegment);
+pub struct CompositeIndex<'a>(&'a DynIndexSegment);
 
 impl<'a> CompositeIndex<'a> {
-    pub(super) fn new(segment: &'a dyn IndexSegment) -> Self {
+    pub(super) fn new(segment: &'a DynIndexSegment) -> Self {
         CompositeIndex(segment)
     }
 
@@ -113,10 +115,10 @@ impl<'a> CompositeIndex<'a> {
     }
 
     /// Iterates self and its ancestor index segments.
-    pub(super) fn ancestor_index_segments(&self) -> impl Iterator<Item = &'a dyn IndexSegment> {
+    pub(super) fn ancestor_index_segments(&self) -> impl Iterator<Item = &'a DynIndexSegment> {
         iter::once(self.0).chain(
             self.ancestor_files_without_local()
-                .map(|file| file.as_ref() as &dyn IndexSegment),
+                .map(|file| file.as_ref() as &DynIndexSegment),
         )
     }
 

lib/src/default_index/entry.rs

@@ -19,7 +19,7 @@ use std::hash::{Hash, Hasher};
 
 use smallvec::SmallVec;
 
-use super::composite::{CompositeIndex, IndexSegment};
+use super::composite::{CompositeIndex, DynIndexSegment};
 use crate::backend::{ChangeId, CommitId};
 use crate::object_id::ObjectId;
 
@@ -43,7 +43,7 @@ pub(super) type SmallLocalPositionsVec = SmallVec<[LocalPosition; 4]>;
 
 #[derive(Clone)]
 pub struct IndexEntry<'a> {
-    source: &'a dyn IndexSegment,
+    source: &'a DynIndexSegment,
     pos: IndexPosition,
     /// Position within the source segment
     local_pos: LocalPosition,
@@ -75,7 +75,7 @@ impl Hash for IndexEntry<'_> {
 
 impl<'a> IndexEntry<'a> {
     pub(super) fn new(
-        source: &'a dyn IndexSegment,
+        source: &'a DynIndexSegment,
         pos: IndexPosition,
         local_pos: LocalPosition,
     ) -> Self {

lib/src/default_index/mod.rs

@@ -37,7 +37,7 @@ mod tests {
     use smallvec::smallvec_inline;
     use test_case::test_case;
 
-    use super::composite::IndexSegment;
+    use super::composite::{DynIndexSegment, IndexSegment};
     use super::entry::SmallIndexPositionsVec;
     use super::mutable::MutableIndexSegment;
     use super::*;
@@ -63,7 +63,7 @@ mod tests {
     fn index_empty(on_disk: bool) {
         let temp_dir = testutils::new_temp_dir();
         let mutable_segment = MutableIndexSegment::full(3, 16);
-        let index_segment: Box<dyn IndexSegment> = if on_disk {
+        let index_segment: Box<DynIndexSegment> = if on_disk {
             let saved_index = mutable_segment.save_in(temp_dir.path()).unwrap();
             Box::new(Arc::try_unwrap(saved_index).unwrap())
         } else {
@@ -94,7 +94,7 @@ mod tests {
         let id_0 = CommitId::from_hex("000000");
         let change_id0 = new_change_id();
         mutable_segment.add_commit_data(id_0.clone(), change_id0.clone(), &[]);
-        let index_segment: Box<dyn IndexSegment> = if on_disk {
+        let index_segment: Box<DynIndexSegment> = if on_disk {
             let saved_index = mutable_segment.save_in(temp_dir.path()).unwrap();
             Box::new(Arc::try_unwrap(saved_index).unwrap())
         } else {
@@ -179,7 +179,7 @@ mod tests {
         mutable_segment.add_commit_data(id_3.clone(), change_id3.clone(), &[id_2.clone()]);
         mutable_segment.add_commit_data(id_4.clone(), change_id4, &[id_1.clone()]);
         mutable_segment.add_commit_data(id_5.clone(), change_id5, &[id_4.clone(), id_2.clone()]);
-        let index_segment: Box<dyn IndexSegment> = if on_disk {
+        let index_segment: Box<DynIndexSegment> = if on_disk {
             let saved_index = mutable_segment.save_in(temp_dir.path()).unwrap();
             Box::new(Arc::try_unwrap(saved_index).unwrap())
         } else {
@@ -291,7 +291,7 @@ mod tests {
             new_change_id(),
             &[id_1, id_2, id_3, id_4, id_5],
         );
-        let index_segment: Box<dyn IndexSegment> = if on_disk {
+        let index_segment: Box<DynIndexSegment> = if on_disk {
             let saved_index = mutable_segment.save_in(temp_dir.path()).unwrap();
             Box::new(Arc::try_unwrap(saved_index).unwrap())
         } else {

lib/src/default_index/mutable.rs

@@ -29,7 +29,9 @@ use itertools::Itertools;
 use smallvec::{smallvec, SmallVec};
 use tempfile::NamedTempFile;
 
-use super::composite::{AsCompositeIndex, ChangeIdIndexImpl, CompositeIndex, IndexSegment};
+use super::composite::{
+    AsCompositeIndex, ChangeIdIndexImpl, CompositeIndex, DynIndexSegment, IndexSegment,
+};
 use super::entry::{IndexPosition, LocalPosition, SmallIndexPositionsVec, SmallLocalPositionsVec};
 use super::readonly::{
     DefaultReadonlyIndex, ReadonlyIndexSegment, INDEX_SEGMENT_FILE_FORMAT_VERSION, OVERFLOW_FLAG,
@@ -137,7 +139,7 @@ impl MutableIndexSegment {
         self.graph.push(entry);
     }
 
-    pub(super) fn add_commits_from(&mut self, other_segment: &dyn IndexSegment) {
+    pub(super) fn add_commits_from(&mut self, other_segment: &DynIndexSegment) {
         let other = CompositeIndex::new(other_segment);
         for pos in other_segment.num_parent_commits()..other.num_commits() {
             let entry = other.entry_by_pos(IndexPosition(pos));