cleanup: fix issues found by latest rustc and clippy

lib/src/backend.rs

@@ -172,7 +172,7 @@ pub struct ConflictPart {
     pub value: TreeValue,
 }
 
-#[derive(Debug, PartialEq, Eq, Clone)]
+#[derive(Default, Debug, PartialEq, Eq, Clone)]
 pub struct Conflict {
     // A conflict is represented by a list of positive and negative states that need to be applied.
     // In a simple 3-way merge of B and C with merge base A, the conflict will be { add: [B, C],
@@ -182,15 +182,6 @@ pub struct Conflict {
     pub adds: Vec<ConflictPart>,
 }
 
-impl Default for Conflict {
-    fn default() -> Self {
-        Conflict {
-            removes: Default::default(),
-            adds: Default::default(),
-        }
-    }
-}
-
 #[derive(Debug, Error, PartialEq, Eq)]
 pub enum BackendError {
     #[error("Object not found")]
@@ -244,19 +235,11 @@ impl<'a> Iterator for TreeEntriesNonRecursiveIter<'a> {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Default, Debug, Clone)]
 pub struct Tree {
     entries: BTreeMap<RepoPathComponent, TreeValue>,
 }
 
-impl Default for Tree {
-    fn default() -> Self {
-        Self {
-            entries: BTreeMap::new(),
-        }
-    }
-}
-
 impl Tree {
     pub fn is_empty(&self) -> bool {
         self.entries.is_empty()

lib/src/op_store.rs

@@ -87,7 +87,7 @@ impl RefTarget {
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Debug)]
+#[derive(Default, PartialEq, Eq, Clone, Debug)]
 pub struct BranchTarget {
     /// The commit the branch points to locally. `None` if the branch has been
     /// deleted locally.
@@ -99,15 +99,6 @@ pub struct BranchTarget {
     pub remote_targets: BTreeMap<String, RefTarget>,
 }
 
-impl Default for BranchTarget {
-    fn default() -> Self {
-        BranchTarget {
-            local_target: None,
-            remote_targets: Default::default(),
-        }
-    }
-}
-
 /// Represents the way the repo looks at a given time, just like how a Tree
 /// object represents how the file system looks at a given time.
 #[derive(PartialEq, Eq, Clone, Debug)]

lib/src/settings.rs

@@ -21,7 +21,7 @@ pub struct UserSettings {
 
 #[derive(Debug, Clone)]
 pub struct RepoSettings {
-    config: config::Config,
+    _config: config::Config,
 }
 
 impl UserSettings {
@@ -51,7 +51,7 @@ impl UserSettings {
                 .format(config::FileFormat::Toml),
         )?;
 
-        Ok(RepoSettings { config })
+        Ok(RepoSettings { _config: config })
     }
 
     pub fn user_name(&self) -> String {