Rollup merge of #62249 - czipperz:use-mem-take-instead-of-replace-default, r=dtolnay,Centril

Use mem::take instead of mem::replace with default

5 files changed, 7 insertions, 6 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 5473f55aa33..c0f721b466e 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -307,7 +307,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             } else {
                 self.resolve_imports();
                 if undetermined_invocations.is_empty() { break }
-                invocations = mem::replace(&mut undetermined_invocations, Vec::new());
+                invocations = mem::take(&mut undetermined_invocations);
                 force = !mem::replace(&mut progress, false);
                 continue
             };
diff --git a/src/libsyntax/ext/tt/transcribe.rs b/src/libsyntax/ext/tt/transcribe.rs
index ea7f8e356aa..e04fd2ddc05 100644
--- a/src/libsyntax/ext/tt/transcribe.rs
+++ b/src/libsyntax/ext/tt/transcribe.rs
@@ -249,7 +249,7 @@ pub fn transcribe(
             quoted::TokenTree::Delimited(mut span, delimited) => {
                 span = span.apply_mark(cx.current_expansion.mark);
                 stack.push(Frame::Delimited { forest: delimited, idx: 0, span });
-                result_stack.push(mem::replace(&mut result, Vec::new()));
+                result_stack.push(mem::take(&mut result));
             }
 
             // Nothing much to do here. Just push the token to the result, being careful to
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 1fe3dfa40ee..7f16bb9dc12 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -17,6 +17,7 @@
 #![feature(const_transmute)]
 #![feature(crate_visibility_modifier)]
 #![feature(label_break_value)]
+#![feature(mem_take)]
 #![feature(nll)]
 #![feature(rustc_attrs)]
 #![feature(rustc_diagnostic_macros)]
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 696b5f48385..8ac20f33908 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -7699,7 +7699,7 @@ impl<'a> Parser<'a> {
         let mut tokens = Vec::new();
         let prev_collecting = match self.token_cursor.frame.last_token {
             LastToken::Collecting(ref mut list) => {
-                Some(mem::replace(list, Vec::new()))
+                Some(mem::take(list))
             }
             LastToken::Was(ref mut last) => {
                 tokens.extend(last.take());
@@ -7717,7 +7717,7 @@ impl<'a> Parser<'a> {
 
         // Pull out the tokens that we've collected from the call to `f` above.
         let mut collected_tokens = match *last_token {
-            LastToken::Collecting(ref mut v) => mem::replace(v, Vec::new()),
+            LastToken::Collecting(ref mut v) => mem::take(v),
             LastToken::Was(_) => panic!("our vector went away?"),
         };
 
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index f90b76721ee..156fab8834c 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -120,8 +120,8 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
         // We don't want to recurse into anything other than mods, since
         // mods or tests inside of functions will break things
         if let ast::ItemKind::Mod(mut module) = item.node {
-            let tests = mem::replace(&mut self.tests, Vec::new());
-            let tested_submods = mem::replace(&mut self.tested_submods, Vec::new());
+            let tests = mem::take(&mut self.tests);
+            let tested_submods = mem::take(&mut self.tested_submods);
             noop_visit_mod(&mut module, self);
             let tests = mem::replace(&mut self.tests, tests);
             let tested_submods = mem::replace(&mut self.tested_submods, tested_submods);