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.
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
end_of_line = lf
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
end_of_line = lf
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false
end_of_line = lf