changeset 51619:b08c5fbe0e70 stable

rust: blanket implementation of Graph for Graph references

The need comes from the fact that `AncestorsIterator` and many
Graph-related algorithms take ownership of the `Graph` they work with.
This, in turn is due to them needing to accept the `Index` instances
that are provided by the Python layers (that neither rhg nor `RHGitaly`
use, of course): the fact that nowadays the Python layer holds an object
that is itself implemented in Rust does not change the core problem that
they cannot be tracked by the borrow checker.

Even though it looks like cloning `Changelog` would be cheap, it seems
hard to guarantee that on the long run. The object is already too rich
for us to be comfortable with it, when using references is the most
natural and guaranteed way of proceeding.

The added test seems a bit superfleous, but it will act as a reminder
that this feature is really useful until something in the Mercurial code
base actually uses it.

--- a/rust/hg-core/src/ancestors.rs	Mon May 06 15:30:21 2024 +0200
+++ b/rust/hg-core/src/ancestors.rs	Mon Apr 22 19:47:08 2024 +0200
@@ -423,6 +423,18 @@
             ),
             vec![8, 7, 4, 3, 2, 1, 0]
         );
+        // it works as well on references, because &Graph implements Graph
+        // this is needed as of this writing by RHGitaly
+        assert_eq!(
+            list_ancestors(
+                &SampleGraph,
+                vec![11.into(), 13.into()],
+                0.into(),
+                false
+            ),
+            vec![8, 7, 4, 3, 2, 1, 0]
+        );
+
         assert_eq!(
             list_ancestors(
                 SampleGraph,

--- a/rust/hg-core/src/revlog/mod.rs	Mon May 06 15:30:21 2024 +0200
+++ b/rust/hg-core/src/revlog/mod.rs	Mon Apr 22 19:47:08 2024 +0200
@@ -132,6 +132,12 @@
     ParentOutOfRange(Revision),
 }
 
+impl<T: Graph> Graph for &T {
+    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
+        (*self).parents(rev)
+    }
+}
+
 /// The Mercurial Revlog Index
 ///
 /// This is currently limited to the minimal interface that is needed for