Auto merge of #26904 - bluss:no-repeat, r=alexcrichton

In a followup to PR #26849, improve one more location for I/O where
we can use `Vec::resize` to ensure better performance when zeroing
buffers.

Use the `vec![elt; n]` macro everywhere we can in the tree. It replaces
`repeat(elt).take(n).collect()` which is more verbose, requires type
hints, and right now produces worse code. `vec![]` is preferable for vector
initialization.

The `vec![]` replacement touches upon one I/O path too, Stdin::read
for windows, and that should be a small improvement.

r? @alexcrichton 

2 files changed, 4 insertions, 6 deletions

diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 86e72d4ef03..5b972b464c9 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -23,7 +23,6 @@ use parse::token;
 use ptr::P;
 
 use std::collections::HashMap;
-use std::iter::repeat;
 
 #[derive(PartialEq)]
 enum ArgumentType {
@@ -469,7 +468,7 @@ impl<'a, 'b> Context<'a, 'b> {
     /// to
     fn into_expr(mut self) -> P<ast::Expr> {
         let mut locals = Vec::new();
-        let mut names: Vec<_> = repeat(None).take(self.name_positions.len()).collect();
+        let mut names = vec![None; self.name_positions.len()];
         let mut pats = Vec::new();
         let mut heads = Vec::new();
 
diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index ed9937c53f4..7c5a46465f5 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -61,7 +61,6 @@
 
 use std::io;
 use std::string;
-use std::iter::repeat;
 
 #[derive(Clone, Copy, PartialEq)]
 pub enum Breaks {
@@ -166,9 +165,9 @@ pub fn mk_printer<'a>(out: Box<io::Write+'a>, linewidth: usize) -> Printer<'a> {
     // fall behind.
     let n: usize = 3 * linewidth;
     debug!("mk_printer {}", linewidth);
-    let token: Vec<Token> = repeat(Token::Eof).take(n).collect();
-    let size: Vec<isize> = repeat(0).take(n).collect();
-    let scan_stack: Vec<usize> = repeat(0).take(n).collect();
+    let token = vec![Token::Eof; n];
+    let size = vec![0_isize; n];
+    let scan_stack = vec![0_usize; n];
     Printer {
         out: out,
         buf_len: n,