Use mem::take to replace with Default values

src/cargo/core/compiler/unit_dependencies.rs

@@ -119,10 +119,7 @@ fn calc_deps_of_std(
         deps_of_roots(roots, &mut state)?;
     }
     state.is_std = false;
-    Ok(Some(std::mem::replace(
-        &mut state.unit_dependencies,
-        HashMap::new(),
-    )))
+    Ok(Some(std::mem::take(&mut state.unit_dependencies)))
 }
 
 /// Add the standard library units to the `unit_dependencies`.

src/cargo/core/package.rs

@@ -735,7 +735,7 @@ impl<'a, 'cfg> Downloads<'a, 'cfg> {
                 .pending
                 .remove(&token)
                 .expect("got a token for a non-in-progress transfer");
-            let data = mem::replace(&mut *dl.data.borrow_mut(), Vec::new());
+            let data = mem::take(&mut *dl.data.borrow_mut());
             let mut handle = self.set.multi.remove(handle)?;
             self.pending_ids.remove(&dl.id);
 

src/cargo/core/summary.rs

@@ -115,8 +115,7 @@ impl Summary {
     {
         {
             let slot = &mut Rc::make_mut(&mut self.inner).dependencies;
-            let deps = mem::replace(slot, Vec::new());
-            *slot = deps.into_iter().map(f).collect();
+            *slot = mem::take(slot).into_iter().map(f).collect();
         }
         self
     }

src/cargo/util/config/mod.rs

@@ -1452,12 +1452,10 @@ impl ConfigValue {
     fn merge(&mut self, from: ConfigValue, force: bool) -> CargoResult<()> {
         match (self, from) {
             (&mut CV::List(ref mut old, _), CV::List(ref mut new, _)) => {
-                let new = mem::replace(new, Vec::new());
-                old.extend(new.into_iter());
+                old.extend(mem::take(new).into_iter());
             }
             (&mut CV::Table(ref mut old, _), CV::Table(ref mut new, _)) => {
-                let new = mem::replace(new, HashMap::new());
-                for (key, value) in new {
+                for (key, value) in mem::take(new) {
                     match old.entry(key.clone()) {
                         Occupied(mut entry) => {
                             let new_def = value.definition().clone();

src/cargo/util/profile.rs

@@ -48,11 +48,7 @@ impl Drop for Profiler {
         let duration = start.elapsed();
         let duration_ms = duration.as_secs() * 1000 + u64::from(duration.subsec_millis());
 
-        let msg = (
-            stack_len,
-            duration_ms,
-            mem::replace(&mut self.desc, String::new()),
-        );
+        let msg = (stack_len, duration_ms, mem::take(&mut self.desc));
         MESSAGES.with(|msgs| msgs.borrow_mut().push(msg));
 
         if stack_len == 0 {