diff --git a/src/libcore/tests/num/dec2flt/parse.rs b/src/libcore/tests/num/dec2flt/parse.rs
index 09acf2bc517b0..3ad694e38adb0 100644
--- a/src/libcore/tests/num/dec2flt/parse.rs
+++ b/src/libcore/tests/num/dec2flt/parse.rs
@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::iter;
 use core::num::dec2flt::parse::{Decimal, parse_decimal};
 use core::num::dec2flt::parse::ParseResult::{Valid, Invalid};
 
@@ -46,7 +45,7 @@ fn valid() {
     assert_eq!(parse_decimal("1.e300"), Valid(Decimal::new(b"1", b"", 300)));
     assert_eq!(parse_decimal(".1e300"), Valid(Decimal::new(b"", b"1", 300)));
     assert_eq!(parse_decimal("101e-33"), Valid(Decimal::new(b"101", b"", -33)));
-    let zeros: String = iter::repeat('0').take(25).collect();
+    let zeros = "0".repeat(25);
     let s = format!("1.5e{}", zeros);
     assert_eq!(parse_decimal(&s), Valid(Decimal::new(b"1", b"5", 0)));
 }
diff --git a/src/librustc/dep_graph/dep_node.rs b/src/librustc/dep_graph/dep_node.rs
index 78e57c6a5d78f..14a818ddafb71 100644
--- a/src/librustc/dep_graph/dep_node.rs
+++ b/src/librustc/dep_graph/dep_node.rs
@@ -334,11 +334,8 @@ macro_rules! define_dep_nodes {
             pub fn extract_def_id(&self, tcx: TyCtxt) -> Option<DefId> {
                 if self.kind.can_reconstruct_query_key() {
                     let def_path_hash = DefPathHash(self.hash);
-                    if let Some(ref def_path_map) = tcx.def_path_hash_to_def_id.as_ref() {
-                        def_path_map.get(&def_path_hash).cloned()
-                    } else {
-                       None
-                    }
+                    tcx.def_path_hash_to_def_id.as_ref()?
+                        .get(&def_path_hash).cloned()
                 } else {
                     None
                 }
diff --git a/src/librustc/dep_graph/graph.rs b/src/librustc/dep_graph/graph.rs
index 1721d1dd0e9c5..e308f2924a05c 100644
--- a/src/librustc/dep_graph/graph.rs
+++ b/src/librustc/dep_graph/graph.rs
@@ -489,7 +489,12 @@ impl DepGraph {
     }
 
     pub(super) fn dep_node_debug_str(&self, dep_node: DepNode) -> Option<String> {
-        self.data.as_ref().and_then(|t| t.dep_node_debug.borrow().get(&dep_node).cloned())
+        self.data
+            .as_ref()?
+            .dep_node_debug
+            .borrow()
+            .get(&dep_node)
+            .cloned()
     }
 
     pub fn edge_deduplication_data(&self) -> (u64, u64) {
diff --git a/src/librustc/hir/pat_util.rs b/src/librustc/hir/pat_util.rs
index 14989f1ff7d8a..8a714a5fbd847 100644
--- a/src/librustc/hir/pat_util.rs
+++ b/src/librustc/hir/pat_util.rs
@@ -47,7 +47,7 @@ impl<T: ExactSizeIterator> EnumerateAndAdjustIterator for T {
         let actual_len = self.len();
         EnumerateAndAdjust {
             enumerate: self.enumerate(),
-            gap_pos: if let Some(gap_pos) = gap_pos { gap_pos } else { expected_len },
+            gap_pos: gap_pos.unwrap_or(expected_len),
             gap_len: expected_len - actual_len,
         }
     }
diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs
index 4ad60f2f85e2c..c46492895dd21 100644
--- a/src/librustc/infer/error_reporting/mod.rs
+++ b/src/librustc/infer/error_reporting/mod.rs
@@ -805,7 +805,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     //     Foo<_, Qux>
                     //         ^ elided type as this type argument was the same in both sides
                     let type_arguments = sub1.types().zip(sub2.types());
-                    let regions_len = sub1.regions().collect::<Vec<_>>().len();
+                    let regions_len = sub1.regions().count();
                     for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() {
                         let i = i + regions_len;
                         if ta1 == ta2 {
diff --git a/src/librustc/util/common.rs b/src/librustc/util/common.rs
index 85533caffce2e..857cabe18b1e2 100644
--- a/src/librustc/util/common.rs
+++ b/src/librustc/util/common.rs
@@ -17,7 +17,6 @@ use std::collections::HashMap;
 use std::ffi::CString;
 use std::fmt::Debug;
 use std::hash::{Hash, BuildHasher};
-use std::iter::repeat;
 use std::panic;
 use std::env;
 use std::path::Path;
@@ -219,7 +218,7 @@ fn print_time_passes_entry_internal(what: &str, dur: Duration) {
         None => "".to_owned(),
     };
     println!("{}time: {}{}\t{}",
-             repeat("  ").take(indentation).collect::<String>(),
+             "  ".repeat(indentation),
              duration_to_secs_str(dur),
              mem_string,
              what);
diff --git a/src/librustc_codegen_llvm/back/symbol_export.rs b/src/librustc_codegen_llvm/back/symbol_export.rs
index 94357f348497d..48de2f3beedfb 100644
--- a/src/librustc_codegen_llvm/back/symbol_export.rs
+++ b/src/librustc_codegen_llvm/back/symbol_export.rs
@@ -206,9 +206,8 @@ fn exported_symbols_provider_local<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                  })
                                  .collect();
 
-    if let Some(_) = *tcx.sess.entry_fn.borrow() {
-        let symbol_name = "main".to_string();
-        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(&symbol_name));
+    if tcx.sess.entry_fn.borrow().is_some() {
+        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new("main"));
 
         symbols.push((exported_symbol, SymbolExportLevel::C));
     }
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index 000025c49a698..3ec73059721a2 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -98,7 +98,6 @@ use std::error::Error;
 use std::ffi::OsString;
 use std::fmt::{self, Display};
 use std::io::{self, Read, Write};
-use std::iter::repeat;
 use std::mem;
 use std::panic;
 use std::path::{PathBuf, Path};
@@ -1229,7 +1228,7 @@ Available lint options:
     fn sort_lint_groups(lints: Vec<(&'static str, Vec<lint::LintId>, bool)>)
                         -> Vec<(&'static str, Vec<lint::LintId>)> {
         let mut lints: Vec<_> = lints.into_iter().map(|(x, y, _)| (x, y)).collect();
-        lints.sort_by_key(|ref l| l.0);
+        lints.sort_by_key(|l| l.0);
         lints
     }
 
@@ -1253,9 +1252,7 @@ Available lint options:
                              .max()
                              .unwrap_or(0);
     let padded = |x: &str| {
-        let mut s = repeat(" ")
-                        .take(max_name_len - x.chars().count())
-                        .collect::<String>();
+        let mut s = " ".repeat(max_name_len - x.chars().count());
         s.push_str(x);
         s
     };
@@ -1287,9 +1284,7 @@ Available lint options:
                                         .unwrap_or(0));
 
     let padded = |x: &str| {
-        let mut s = repeat(" ")
-                        .take(max_name_len - x.chars().count())
-                        .collect::<String>();
+        let mut s = " ".repeat(max_name_len - x.chars().count());
         s.push_str(x);
         s
     };
diff --git a/src/librustc_driver/profile/trace.rs b/src/librustc_driver/profile/trace.rs
index 4aaf5eb47f61c..970a860fdff2c 100644
--- a/src/librustc_driver/profile/trace.rs
+++ b/src/librustc_driver/profile/trace.rs
@@ -208,7 +208,7 @@ pub fn write_counts(count_file: &mut File, counts: &mut HashMap<String,QueryMetr
     for (ref cons, ref qm) in counts.iter() {
         data.push((cons.clone(), qm.count.clone(), qm.dur_total.clone(), qm.dur_self.clone()));
     };
-    data.sort_by_key(|&k| Reverse(k.3));
+    data.sort_by_key(|k| Reverse(k.3));
     for (cons, count, dur_total, dur_self) in data {
         write!(count_file, "{}, {}, {}, {}\n",
                cons, count,
diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index 6bcf0d9eff6c5..e0ed89a641659 100644
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -528,9 +528,7 @@ impl EmitterWriter {
 
         // If there are no annotations or the only annotations on this line are
         // MultilineLine, then there's only code being shown, stop processing.
-        if line.annotations.is_empty() || line.annotations.iter()
-            .filter(|a| !a.is_line()).collect::<Vec<_>>().len() == 0
-        {
+        if line.annotations.iter().all(|a| a.is_line()) {
             return vec![];
         }
 
@@ -901,9 +899,7 @@ impl EmitterWriter {
         //    |  |   length of label
         //    |  magic `3`
         //    `max_line_num_len`
-        let padding = (0..padding + label.len() + 5)
-            .map(|_| " ")
-            .collect::<String>();
+        let padding = " ".repeat(padding + label.len() + 5);
 
         /// Return whether `style`, or the override if present and the style is `NoStyle`.
         fn style_or_override(style: Style, override_style: Option<Style>) -> Style {
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index c0f07645f496a..400e5829d3337 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -610,9 +610,8 @@ impl Handler {
         if can_show_explain && are_there_diagnostics {
             let mut error_codes =
                 self.emitted_diagnostic_codes.borrow()
-                                             .clone()
-                                             .into_iter()
-                                             .filter_map(|x| match x {
+                                             .iter()
+                                             .filter_map(|x| match *x {
                                                  DiagnosticId::Error(ref s) => Some(s.clone()),
                                                  _ => None,
                                              })
diff --git a/src/librustc_lint/bad_style.rs b/src/librustc_lint/bad_style.rs
index fd5a152311ded..09871c0e84049 100644
--- a/src/librustc_lint/bad_style.rs
+++ b/src/librustc_lint/bad_style.rs
@@ -83,12 +83,10 @@ impl NonCamelCaseTypes {
                     } else {
                         c.to_lowercase().collect()
                     })
-                    .collect::<Vec<_>>()
-                    .concat()
+                    .collect::<String>()
                 })
                 .filter(|x| !x.is_empty())
-                .collect::<Vec<_>>()
-                .iter().fold((String::new(), None), |(acc, prev): (String, Option<&String>), next| {
+                .fold((String::new(), None), |(acc, prev): (String, Option<String>), next| {
                     // separate two components with an underscore if their boundary cannot
                     // be distinguished using a uppercase/lowercase case distinction
                     let join = if let Some(prev) = prev {
@@ -96,7 +94,7 @@ impl NonCamelCaseTypes {
                                     let f = next.chars().next().unwrap();
                                     !char_has_case(l) && !char_has_case(f)
                                 } else { false };
-                    (acc + if join { "_" } else { "" } + next, Some(next))
+                    (acc + if join { "_" } else { "" } + &next, Some(next))
                 }).0
         }
 
diff --git a/src/librustc_mir/hair/pattern/_match.rs b/src/librustc_mir/hair/pattern/_match.rs
index 83361ea57c371..5d45955771185 100644
--- a/src/librustc_mir/hair/pattern/_match.rs
+++ b/src/librustc_mir/hair/pattern/_match.rs
@@ -32,7 +32,7 @@ use arena::TypedArena;
 
 use std::cmp::{self, Ordering};
 use std::fmt;
-use std::iter::{FromIterator, IntoIterator, repeat};
+use std::iter::{FromIterator, IntoIterator};
 
 pub fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pattern<'tcx>)
                                 -> &'a Pattern<'tcx>
@@ -115,7 +115,7 @@ impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> {
         }).collect();
 
         let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1;
-        let br = repeat('+').take(total_width).collect::<String>();
+        let br = "+".repeat(total_width);
         write!(f, "{}\n", br)?;
         for row in pretty_printed_matrix {
             write!(f, "+")?;
diff --git a/src/librustc_mir/monomorphize/mod.rs b/src/librustc_mir/monomorphize/mod.rs
index e148bc3d9460c..30556759bd394 100644
--- a/src/librustc_mir/monomorphize/mod.rs
+++ b/src/librustc_mir/monomorphize/mod.rs
@@ -29,13 +29,13 @@ pub fn assert_symbols_are_distinct<'a, 'tcx, I>(tcx: TyCtxt<'a, 'tcx, 'tcx>, mon
         (mono_item, mono_item.symbol_name(tcx))
     }).collect();
 
-    (&mut symbols[..]).sort_by_key(|&sym| sym.1);
+    symbols.sort_by_key(|sym| sym.1);
 
-    for pair in (&symbols[..]).windows(2) {
+    for pair in symbols.windows(2) {
         let sym1 = &pair[0].1;
         let sym2 = &pair[1].1;
 
-        if *sym1 == *sym2 {
+        if sym1 == sym2 {
             let mono_item1 = pair[0].0;
             let mono_item2 = pair[1].0;
 
@@ -51,9 +51,7 @@ pub fn assert_symbols_are_distinct<'a, 'tcx, I>(tcx: TyCtxt<'a, 'tcx, 'tcx>, mon
                         span2
                     })
                 }
-                (Some(span), None) |
-                (None, Some(span)) => Some(span),
-                _ => None
+                (span1, span2) => span1.or(span2),
             };
 
             let error_message = format!("symbol `{}` is already defined", sym1);
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 765016fdc4a74..d8b9c58950f51 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -271,7 +271,7 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver,
             err
         }
         ResolutionError::VariableNotBoundInPattern(binding_error) => {
-            let target_sp = binding_error.target.iter().map(|x| *x).collect::<Vec<_>>();
+            let target_sp = binding_error.target.iter().cloned().collect::<Vec<_>>();
             let msp = MultiSpan::from_spans(target_sp.clone());
             let msg = format!("variable `{}` is not bound in all patterns", binding_error.name);
             let mut err = resolver.session.struct_span_err_with_code(
@@ -282,7 +282,7 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver,
             for sp in target_sp {
                 err.span_label(sp, format!("pattern doesn't bind `{}`", binding_error.name));
             }
-            let origin_sp = binding_error.origin.iter().map(|x| *x).collect::<Vec<_>>();
+            let origin_sp = binding_error.origin.iter().cloned();
             for sp in origin_sp {
                 err.span_label(sp, "variable not in all patterns");
             }
diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 2377354b85f6b..0a25e9091deef 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -16,7 +16,6 @@
 //! them in the future to instead emit any format desired.
 
 use std::fmt;
-use std::iter::repeat;
 
 use rustc::hir::def_id::DefId;
 use rustc_target::spec::abi::Abi;
@@ -235,10 +234,9 @@ impl<'a> fmt::Display for WhereClause<'a> {
 
         if !f.alternate() {
             clause.push_str("</span>");
-            let padding = repeat("&nbsp;").take(indent + 4).collect::<String>();
+            let padding = "&nbsp;".repeat(indent + 4);
             clause = clause.replace("<br>", &format!("<br>{}", padding));
-            clause.insert_str(0, &repeat("&nbsp;").take(indent.saturating_sub(1))
-                                                  .collect::<String>());
+            clause.insert_str(0, &"&nbsp;".repeat(indent.saturating_sub(1)));
             if !end_newline {
                 clause.insert_str(0, "<br>");
             }
@@ -409,13 +407,13 @@ pub fn href(did: DefId) -> Option<(String, ItemType, Vec<String>)> {
     let loc = CURRENT_LOCATION_KEY.with(|l| l.borrow().clone());
     let (fqp, shortty, mut url) = match cache.paths.get(&did) {
         Some(&(ref fqp, shortty)) => {
-            (fqp, shortty, repeat("../").take(loc.len()).collect())
+            (fqp, shortty, "../".repeat(loc.len()))
         }
         None => {
             let &(ref fqp, shortty) = cache.external_paths.get(&did)?;
             (fqp, shortty, match cache.extern_locations[&did.krate] {
                 (.., render::Remote(ref s)) => s.to_string(),
-                (.., render::Local) => repeat("../").take(loc.len()).collect(),
+                (.., render::Local) => "../".repeat(loc.len()),
                 (.., render::Unknown) => return None,
             })
         }
@@ -481,7 +479,7 @@ fn primitive_link(f: &mut fmt::Formatter,
                 let len = CURRENT_LOCATION_KEY.with(|s| s.borrow().len());
                 let len = if len == 0 {0} else {len - 1};
                 write!(f, "<a class=\"primitive\" href=\"{}primitive.{}.html\">",
-                       repeat("../").take(len).collect::<String>(),
+                       "../".repeat(len),
                        prim.to_url_str())?;
                 needs_termination = true;
             }
@@ -492,7 +490,7 @@ fn primitive_link(f: &mut fmt::Formatter,
                     }
                     (ref cname, _, render::Local) => {
                         let len = CURRENT_LOCATION_KEY.with(|s| s.borrow().len());
-                        Some((cname, repeat("../").take(len).collect::<String>()))
+                        Some((cname, "../".repeat(len)))
                     }
                     (.., render::Unknown) => None,
                 };
@@ -903,15 +901,15 @@ impl<'a> fmt::Display for Method<'a> {
             format!("{}", decl.output)
         };
 
-        let pad = repeat(" ").take(name_len).collect::<String>();
+        let pad = " ".repeat(name_len);
         let plain = format!("{pad}({args}){arrow}",
                         pad = pad,
                         args = args_plain,
                         arrow = arrow_plain);
 
         let output = if plain.len() > 80 {
-            let full_pad = format!("<br>{}", repeat("&nbsp;").take(indent + 4).collect::<String>());
-            let close_pad = format!("<br>{}", repeat("&nbsp;").take(indent).collect::<String>());
+            let full_pad = format!("<br>{}", "&nbsp;".repeat(indent + 4));
+            let close_pad = format!("<br>{}", "&nbsp;".repeat(indent));
             format!("({args}{close}){arrow}",
                     args = args.replace("<br>", &full_pad),
                     close = close_pad,
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index ade33c8dd7d19..c06323b22dc80 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -46,7 +46,6 @@ use std::ffi::OsStr;
 use std::fs::{self, File, OpenOptions};
 use std::io::prelude::*;
 use std::io::{self, BufWriter, BufReader};
-use std::iter::repeat;
 use std::mem;
 use std::path::{PathBuf, Path, Component};
 use std::str;
@@ -1712,7 +1711,7 @@ impl Context {
     /// String representation of how to get back to the root path of the 'doc/'
     /// folder in terms of a relative URL.
     fn root_path(&self) -> String {
-        repeat("../").take(self.current.len()).collect::<String>()
+        "../".repeat(self.current.len())
     }
 
     /// Recurse in the directory structure and change the "root path" to make
@@ -2113,8 +2112,7 @@ impl<'a> fmt::Display for Item<'a> {
             let amt = if self.item.is_mod() { cur.len() - 1 } else { cur.len() };
             for (i, component) in cur.iter().enumerate().take(amt) {
                 write!(fmt, "<a href='{}index.html'>{}</a>::<wbr>",
-                       repeat("../").take(cur.len() - i - 1)
-                                    .collect::<String>(),
+                       "../".repeat(cur.len() - i - 1),
                        component)?;
             }
         }
diff --git a/src/libstd/tests/env.rs b/src/libstd/tests/env.rs
index d4376523691a1..8acb8a46d7bf2 100644
--- a/src/libstd/tests/env.rs
+++ b/src/libstd/tests/env.rs
@@ -11,7 +11,6 @@
 extern crate rand;
 
 use std::env::*;
-use std::iter::repeat;
 use std::ffi::{OsString, OsStr};
 
 use rand::Rng;
@@ -72,7 +71,7 @@ fn test_var_big() {
 #[cfg_attr(target_os = "emscripten", ignore)]
 fn test_env_set_get_huge() {
     let n = make_rand_name();
-    let s = repeat("x").take(10000).collect::<String>();
+    let s = "x".repeat(10000);
     set_var(&n, &s);
     eq(var_os(&n), Some(&s));
     remove_var(&n);
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index de68780ef2ca2..0ef390beac950 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -32,7 +32,7 @@ use tokenstream::{self, TokenStream, TokenTree};
 
 use std::ascii;
 use std::io::{self, Write, Read};
-use std::iter::{self, Peekable};
+use std::iter::Peekable;
 use std::vec;
 
 pub enum AnnNode<'a> {
@@ -235,11 +235,11 @@ pub fn token_to_string(tok: &Token) -> String {
                 token::Integer(c)        => c.to_string(),
                 token::Str_(s)           => format!("\"{}\"", s),
                 token::StrRaw(s, n)      => format!("r{delim}\"{string}\"{delim}",
-                                                    delim=repeat("#", n as usize),
+                                                    delim="#".repeat(n as usize),
                                                     string=s),
                 token::ByteStr(v)         => format!("b\"{}\"", v),
                 token::ByteStrRaw(s, n)   => format!("br{delim}\"{string}\"{delim}",
-                                                    delim=repeat("#", n as usize),
+                                                    delim="#".repeat(n as usize),
                                                     string=s),
             };
 
@@ -661,7 +661,7 @@ pub trait PrintState<'a> {
             }
             ast::StrStyle::Raw(n) => {
                 (format!("r{delim}\"{string}\"{delim}",
-                         delim=repeat("#", n as usize),
+                         delim="#".repeat(n as usize),
                          string=st))
             }
         };
@@ -3180,8 +3180,6 @@ impl<'a> State<'a> {
     }
 }
 
-fn repeat(s: &str, n: usize) -> String { iter::repeat(s).take(n).collect() }
-
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index 6b547dff9120e..9f670de4f5b48 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -66,7 +66,6 @@ use std::fmt;
 use std::fs::File;
 use std::io::prelude::*;
 use std::io;
-use std::iter::repeat;
 use std::path::PathBuf;
 use std::process::Termination;
 use std::sync::mpsc::{channel, Sender};
@@ -145,7 +144,7 @@ impl TestDesc {
     fn padded_name(&self, column_count: usize, align: NamePadding) -> String {
         let mut name = String::from(self.name.as_slice());
         let fill = column_count.saturating_sub(name.len());
-        let pad = repeat(" ").take(fill).collect::<String>();
+        let pad = " ".repeat(fill);
         match align {
             PadNone => name,
             PadOnRight => {