fix(backend)!: Use correct merge stratgy for repository options (#291)

This fixes the merge strategy for values of `options`, `options_hot`,
and `options_cold` to ignore incoming elements if they are already
existing in the HashMap. The prior implementation was overwriting the
values.

Breaking change: The freestanding and public `extend` function has been
removed. You can use `conflate::hashmap::overwrite` as a replacement.

---------

Signed-off-by: simonsan <[email protected]>
Co-authored-by: Alexander Weiss <[email protected]>
Co-authored-by: aawsome <[email protected]>

crates/backend/src/choose.rs

@@ -50,33 +50,20 @@ pub struct BackendOptions {
 
     /// Other options for this repository (hot and cold part)
     #[cfg_attr(feature = "clap", clap(skip))]
-    #[cfg_attr(feature = "merge", merge(strategy = extend))]
+    #[cfg_attr(feature = "merge", merge(strategy = conflate::hashmap::ignore))]
     pub options: HashMap<String, String>,
 
     /// Other options for the hot repository
     #[cfg_attr(feature = "clap", clap(skip))]
-    #[cfg_attr(feature = "merge", merge(strategy = extend))]
+    #[cfg_attr(feature = "merge", merge(strategy = conflate::hashmap::ignore))]
     pub options_hot: HashMap<String, String>,
 
     /// Other options for the cold repository
     #[cfg_attr(feature = "clap", clap(skip))]
-    #[cfg_attr(feature = "merge", merge(strategy = extend))]
+    #[cfg_attr(feature = "merge", merge(strategy = conflate::hashmap::ignore))]
     pub options_cold: HashMap<String, String>,
 }
 
-/// Overwrite the left value with the right value
-///
-/// This is used for merging config values, e.g. [`BackendOptions`].
-///
-/// # Arguments
-///
-/// * `left` - The left value
-/// * `right` - The right value
-#[cfg(feature = "merge")]
-pub fn extend<A, T: Extend<A> + IntoIterator<Item = A>>(left: &mut T, right: T) {
-    left.extend(right);
-}
-
 impl BackendOptions {
     /// Convert the options to backends.
     ///