[commitgraph] Loosen lifetime restrictions on return values.

Author: avoidscorn

git-commitgraph/src/file/commit.rs

@@ -77,15 +77,25 @@ impl<'a> Commit<'a> {
         }
     }
 
-    pub fn id(&self) -> borrowed::Id<'_> {
+    // Allow the return value to outlive this Commit object, as it only needs to be bound by the
+    // lifetime of the parent file.
+    pub fn id<'b>(&'b self) -> borrowed::Id<'a>
+    where
+        'a: 'b,
+    {
         self.file.id_at(self.pos)
     }
 
     pub fn parent1(&self) -> Result<Option<graph::Position>, Error> {
         self.iter_parents().next().transpose()
     }
 
-    pub fn root_tree_id(&self) -> borrowed::Id<'_> {
+    // Allow the return value to outlive this Commit object, as it only needs to be bound by the
+    // lifetime of the parent file.
+    pub fn root_tree_id<'b>(&'b self) -> borrowed::Id<'a>
+    where
+        'a: 'b,
+    {
         self.root_tree_id
     }
 }