clippy: fix assigning_clones lint

https://rust-lang.github.io/rust-clippy/master/index.html#assigning_clones

Closes #12267

Cargo.toml

@@ -184,6 +184,7 @@ rust.unstable_name_collisions = "allow"
 rustdoc.private_intra_doc_links = "allow"
 
 [workspace.lints.clippy]
+assigning_clones = "warn"
 implicit_clone = "warn"
 cloned_instead_of_copied = "warn"
 len_without_is_empty = "allow"     # we're not a library crate

src/builtins/set.rs

@@ -890,7 +890,7 @@ fn new_var_values(
         // So do not use the given variable: we must re-fetch it.
         // TODO: this races under concurrent execution.
         if let Some(existing) = vars.get(varname) {
-            result = existing.as_list().to_owned();
+            existing.as_list().clone_into(&mut result);
         }
 
         if opts.prepend {
@@ -914,10 +914,12 @@ fn new_var_values_by_index(split: &SplitVar, argv: &[&wstr]) -> Vec<WString> {
     // Inherit any existing values.
     // Note unlike the append/prepend case, we start with a variable in the same scope as we are
     // setting.
-    let mut result = vec![];
-    if let Some(var) = split.var.as_ref() {
-        result = var.as_list().to_owned();
-    }
+    let mut result = split
+        .var
+        .as_ref()
+        .map(EnvVar::as_list)
+        .unwrap_or_default()
+        .to_owned();
 
     // For each (index, argument) pair, set the element in our `result` to the replacement string.
     // Extend the list with empty strings as needed. The indexes are 1-based.

src/history/history.rs

@@ -281,7 +281,7 @@ fn merge(&mut self, item: &HistoryItem) -> bool {
         // Ok, merge this item.
         self.creation_timestamp = self.creation_timestamp.max(item.creation_timestamp);
         if self.required_paths.len() < item.required_paths.len() {
-            self.required_paths = item.required_paths.clone();
+            self.required_paths.clone_from(&item.required_paths);
         }
         true
     }

src/parse_execution.rs

@@ -453,7 +453,7 @@ fn infinite_recursive_statement_in_job_list<'b>(
             });
 
         if infinite_recursive_statement.is_some() {
-            *out_func_name = forbidden_function_name.to_owned();
+            forbidden_function_name.clone_into(out_func_name);
         }
 
         // may be none
@@ -1865,7 +1865,7 @@ fn setup_group(&self, ctx: &OperationContext<'_>, j: &mut Job) {
             .is_some_and(|job_group| job_group.has_job_id() || !j.wants_job_id())
             && !j.is_initially_background()
         {
-            j.group = ctx.job_group.clone();
+            j.group.clone_from(&ctx.job_group);
             return;
         }