Use `Cow` in `Token::String`.

`Printer::word` takes a `&str` and converts it into a `String`, which
causes an allocation. But that allocation is rarely necessary, because
`&str` is almost always a `&'static str` or a `String` that won't be
used again.

This commit changes `Token::String` so it holds a `Cow<'static, str>`
instead of a `String`, which avoids a lot of allocations.

7 files changed, 101 insertions, 88 deletions

diff --git a/src/librustc/hir/print.rs b/src/librustc/hir/print.rs
index e69d32ad1de..9a0ceddcf1b 100644
--- a/src/librustc/hir/print.rs
+++ b/src/librustc/hir/print.rs
@@ -25,6 +25,7 @@ use hir;
 use hir::{PatKind, GenericBound, TraitBoundModifier, RangeEnd};
 use hir::{GenericParam, GenericParamKind, GenericArg};
 
+use std::borrow::Cow;
 use std::cell::Cell;
 use std::io::{self, Write, Read};
 use std::iter::Peekable;
@@ -209,7 +210,7 @@ pub fn to_string<F>(ann: &dyn PpAnn, f: F) -> String
     String::from_utf8(wr).unwrap()
 }
 
-pub fn visibility_qualified(vis: &hir::Visibility, w: &str) -> String {
+pub fn visibility_qualified<S: Into<Cow<'static, str>>>(vis: &hir::Visibility, w: S) -> String {
     to_string(NO_ANN, |s| {
         s.print_visibility(vis)?;
         s.s.word(w)
@@ -226,12 +227,13 @@ impl<'a> State<'a> {
         self.s.word(" ")
     }
 
-    pub fn word_nbsp(&mut self, w: &str) -> io::Result<()> {
+    pub fn word_nbsp<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
         self.s.word(w)?;
         self.nbsp()
     }
 
-    pub fn head(&mut self, w: &str) -> io::Result<()> {
+    pub fn head<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
+        let w = w.into();
         // outer-box is consistent
         self.cbox(indent_unit)?;
         // head-box is inconsistent
@@ -303,7 +305,7 @@ impl<'a> State<'a> {
     pub fn synth_comment(&mut self, text: String) -> io::Result<()> {
         self.s.word("/*")?;
         self.s.space()?;
-        self.s.word(&text[..])?;
+        self.s.word(text)?;
         self.s.space()?;
         self.s.word("*/")
     }
@@ -468,7 +470,7 @@ impl<'a> State<'a> {
                 self.end() // end the outer fn box
             }
             hir::ForeignItemKind::Static(ref t, m) => {
-                self.head(&visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"))?;
                 if m {
                     self.word_space("mut")?;
                 }
@@ -480,7 +482,7 @@ impl<'a> State<'a> {
                 self.end() // end the outer cbox
             }
             hir::ForeignItemKind::Type => {
-                self.head(&visibility_qualified(&item.vis, "type"))?;
+                self.head(visibility_qualified(&item.vis, "type"))?;
                 self.print_name(item.name)?;
                 self.s.word(";")?;
                 self.end()?; // end the head-ibox
@@ -495,7 +497,7 @@ impl<'a> State<'a> {
                               default: Option<hir::BodyId>,
                               vis: &hir::Visibility)
                               -> io::Result<()> {
-        self.s.word(&visibility_qualified(vis, ""))?;
+        self.s.word(visibility_qualified(vis, ""))?;
         self.word_space("const")?;
         self.print_ident(ident)?;
         self.word_space(":")?;
@@ -534,7 +536,7 @@ impl<'a> State<'a> {
         self.ann.pre(self, AnnNode::Item(item))?;
         match item.node {
             hir::ItemKind::ExternCrate(orig_name) => {
-                self.head(&visibility_qualified(&item.vis, "extern crate"))?;
+                self.head(visibility_qualified(&item.vis, "extern crate"))?;
                 if let Some(orig_name) = orig_name {
                     self.print_name(orig_name)?;
                     self.s.space()?;
@@ -547,7 +549,7 @@ impl<'a> State<'a> {
                 self.end()?; // end outer head-block
             }
             hir::ItemKind::Use(ref path, kind) => {
-                self.head(&visibility_qualified(&item.vis, "use"))?;
+                self.head(visibility_qualified(&item.vis, "use"))?;
                 self.print_path(path, false)?;
 
                 match kind {
@@ -566,7 +568,7 @@ impl<'a> State<'a> {
                 self.end()?; // end outer head-block
             }
             hir::ItemKind::Static(ref ty, m, expr) => {
-                self.head(&visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"))?;
                 if m == hir::MutMutable {
                     self.word_space("mut")?;
                 }
@@ -582,7 +584,7 @@ impl<'a> State<'a> {
                 self.end()?; // end the outer cbox
             }
             hir::ItemKind::Const(ref ty, expr) => {
-                self.head(&visibility_qualified(&item.vis, "const"))?;
+                self.head(visibility_qualified(&item.vis, "const"))?;
                 self.print_name(item.name)?;
                 self.word_space(":")?;
                 self.print_type(&ty)?;
@@ -609,7 +611,7 @@ impl<'a> State<'a> {
                 self.ann.nested(self, Nested::Body(body))?;
             }
             hir::ItemKind::Mod(ref _mod) => {
-                self.head(&visibility_qualified(&item.vis, "mod"))?;
+                self.head(visibility_qualified(&item.vis, "mod"))?;
                 self.print_name(item.name)?;
                 self.nbsp()?;
                 self.bopen()?;
@@ -618,18 +620,18 @@ impl<'a> State<'a> {
             }
             hir::ItemKind::ForeignMod(ref nmod) => {
                 self.head("extern")?;
-                self.word_nbsp(&nmod.abi.to_string())?;
+                self.word_nbsp(nmod.abi.to_string())?;
                 self.bopen()?;
                 self.print_foreign_mod(nmod, &item.attrs)?;
                 self.bclose(item.span)?;
             }
             hir::ItemKind::GlobalAsm(ref ga) => {
-                self.head(&visibility_qualified(&item.vis, "global asm"))?;
-                self.s.word(&ga.asm.as_str())?;
+                self.head(visibility_qualified(&item.vis, "global asm"))?;
+                self.s.word(ga.asm.as_str().get())?;
                 self.end()?
             }
             hir::ItemKind::Ty(ref ty, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "type"))?;
+                self.head(visibility_qualified(&item.vis, "type"))?;
                 self.print_name(item.name)?;
                 self.print_generic_params(&generics.params)?;
                 self.end()?; // end the inner ibox
@@ -642,7 +644,7 @@ impl<'a> State<'a> {
                 self.end()?; // end the outer ibox
             }
             hir::ItemKind::Existential(ref exist) => {
-                self.head(&visibility_qualified(&item.vis, "existential type"))?;
+                self.head(visibility_qualified(&item.vis, "existential type"))?;
                 self.print_name(item.name)?;
                 self.print_generic_params(&exist.generics.params)?;
                 self.end()?; // end the inner ibox
@@ -668,11 +670,11 @@ impl<'a> State<'a> {
                 self.print_enum_def(enum_definition, params, item.name, item.span, &item.vis)?;
             }
             hir::ItemKind::Struct(ref struct_def, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "struct"))?;
+                self.head(visibility_qualified(&item.vis, "struct"))?;
                 self.print_struct(struct_def, generics, item.name, item.span, true)?;
             }
             hir::ItemKind::Union(ref struct_def, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "union"))?;
+                self.head(visibility_qualified(&item.vis, "union"))?;
                 self.print_struct(struct_def, generics, item.name, item.span, true)?;
             }
             hir::ItemKind::Impl(unsafety,
@@ -795,7 +797,7 @@ impl<'a> State<'a> {
                           span: syntax_pos::Span,
                           visibility: &hir::Visibility)
                           -> io::Result<()> {
-        self.head(&visibility_qualified(visibility, "enum"))?;
+        self.head(visibility_qualified(visibility, "enum"))?;
         self.print_name(name)?;
         self.print_generic_params(&generics.params)?;
         self.print_where_clause(&generics.where_clause)?;
@@ -1587,14 +1589,14 @@ impl<'a> State<'a> {
     }
 
     pub fn print_usize(&mut self, i: usize) -> io::Result<()> {
-        self.s.word(&i.to_string())
+        self.s.word(i.to_string())
     }
 
     pub fn print_ident(&mut self, ident: ast::Ident) -> io::Result<()> {
         if ident.is_raw_guess() {
-            self.s.word(&format!("r#{}", ident.name))?;
+            self.s.word(format!("r#{}", ident.name))?;
         } else {
-            self.s.word(&ident.as_str())?;
+            self.s.word(ident.as_str().get())?;
         }
         self.ann.post(self, AnnNode::Name(&ident.name))
     }
@@ -2010,7 +2012,7 @@ impl<'a> State<'a> {
         self.commasep(Inconsistent, &decl.inputs, |s, ty| {
             s.ibox(indent_unit)?;
             if let Some(arg_name) = arg_names.get(i) {
-                s.s.word(&arg_name.as_str())?;
+                s.s.word(arg_name.as_str().get())?;
                 s.s.word(":")?;
                 s.s.space()?;
             } else if let Some(body_id) = body_id {
@@ -2073,7 +2075,8 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_bounds(&mut self, prefix: &str, bounds: &[hir::GenericBound]) -> io::Result<()> {
+    pub fn print_bounds(&mut self, prefix: &'static str, bounds: &[hir::GenericBound])
+                        -> io::Result<()> {
         if !bounds.is_empty() {
             self.s.word(prefix)?;
             let mut first = true;
@@ -2322,7 +2325,7 @@ impl<'a> State<'a> {
             Some(Abi::Rust) => Ok(()),
             Some(abi) => {
                 self.word_nbsp("extern")?;
-                self.word_nbsp(&abi.to_string())
+                self.word_nbsp(abi.to_string())
             }
             None => Ok(()),
         }
@@ -2332,7 +2335,7 @@ impl<'a> State<'a> {
         match opt_abi {
             Some(abi) => {
                 self.word_nbsp("extern")?;
-                self.word_nbsp(&abi.to_string())
+                self.word_nbsp(abi.to_string())
             }
             None => Ok(()),
         }
@@ -2342,7 +2345,7 @@ impl<'a> State<'a> {
                                 header: hir::FnHeader,
                                 vis: &hir::Visibility)
                                 -> io::Result<()> {
-        self.s.word(&visibility_qualified(vis, ""))?;
+        self.s.word(visibility_qualified(vis, ""))?;
 
         match header.constness {
             hir::Constness::NotConst => {}
@@ -2358,7 +2361,7 @@ impl<'a> State<'a> {
 
         if header.abi != Abi::Rust {
             self.word_nbsp("extern")?;
-            self.word_nbsp(&header.abi.to_string())?;
+            self.word_nbsp(header.abi.to_string())?;
         }
 
         self.s.word("fn")
diff --git a/src/librustc_driver/pretty.rs b/src/librustc_driver/pretty.rs
index c7ba31e3395..fb8093d1d77 100644
--- a/src/librustc_driver/pretty.rs
+++ b/src/librustc_driver/pretty.rs
@@ -530,7 +530,7 @@ impl<'a, 'tcx> pprust_hir::PpAnn for TypedAnnotation<'a, 'tcx> {
                 s.s.space()?;
                 s.s.word("as")?;
                 s.s.space()?;
-                s.s.word(&self.tables.get().expr_ty(expr).to_string())?;
+                s.s.word(self.tables.get().expr_ty(expr).to_string())?;
                 s.pclose()
             }
             _ => Ok(()),
diff --git a/src/librustc_typeck/check_unused.rs b/src/librustc_typeck/check_unused.rs
index 22a96d4e908..103331894ff 100644
--- a/src/librustc_typeck/check_unused.rs
+++ b/src/librustc_typeck/check_unused.rs
@@ -185,7 +185,7 @@ fn unused_crates_lint<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) {
             Some(orig_name) => format!("use {} as {};", orig_name, item.name),
             None => format!("use {};", item.name),
         };
-        let replacement = visibility_qualified(&item.vis, &base_replacement);
+        let replacement = visibility_qualified(&item.vis, base_replacement);
         tcx.struct_span_lint_node(lint, id, extern_crate.span, msg)
             .span_suggestion_short_with_applicability(
                 extern_crate.span,
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index e2f09affd4f..99a59fa8a75 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2795,7 +2795,7 @@ impl<'a> Parser<'a> {
                             s.print_usize(float.trunc() as usize)?;
                             s.pclose()?;
                             s.s.word(".")?;
-                            s.s.word(fstr.splitn(2, ".").last().unwrap())
+                            s.s.word(fstr.splitn(2, ".").last().unwrap().to_string())
                         });
                         err.span_suggestion_with_applicability(
                             lo.to(self.prev_span),
diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index e01c4b01aaa..b9addcaeb8e 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -147,6 +147,7 @@
 use std::collections::VecDeque;
 use std::fmt;
 use std::io;
+use std::borrow::Cow;
 
 /// How to break. Described in more detail in the module docs.
 #[derive(Clone, Copy, PartialEq)]
@@ -169,7 +170,10 @@ pub struct BeginToken {
 
 #[derive(Clone)]
 pub enum Token {
-    String(String, isize),
+    // In practice a string token contains either a `&'static str` or a
+    // `String`. `Cow` is overkill for this because we never modify the data,
+    // but it's more convenient than rolling our own more specialized type.
+    String(Cow<'static, str>, isize),
     Break(BreakToken),
     Begin(BeginToken),
     End,
@@ -644,8 +648,10 @@ impl<'a> Printer<'a> {
         self.pretty_print(Token::Eof)
     }
 
-    pub fn word(&mut self, wrd: &str) -> io::Result<()> {
-        self.pretty_print(Token::String(wrd.to_string(), wrd.len() as isize))
+    pub fn word<S: Into<Cow<'static, str>>>(&mut self, wrd: S) -> io::Result<()> {
+        let s = wrd.into();
+        let len = s.len() as isize;
+        self.pretty_print(Token::String(s, len))
     }
 
     fn spaces(&mut self, n: usize) -> io::Result<()> {
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index ce7708cc42e..14ad4b5c6f8 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -29,6 +29,7 @@ use syntax_pos::{DUMMY_SP, FileName};
 use tokenstream::{self, TokenStream, TokenTree};
 
 use std::ascii;
+use std::borrow::Cow;
 use std::io::{self, Write, Read};
 use std::iter::Peekable;
 use std::vec;
@@ -444,7 +445,7 @@ pub trait PrintState<'a> {
     fn cur_lit(&mut self) -> Option<&comments::Literal>;
     fn bump_lit(&mut self) -> Option<comments::Literal>;
 
-    fn word_space(&mut self, w: &str) -> io::Result<()> {
+    fn word_space<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
         self.writer().word(w)?;
         self.writer().space()
     }
@@ -539,7 +540,7 @@ pub trait PrintState<'a> {
             comments::Mixed => {
                 assert_eq!(cmnt.lines.len(), 1);
                 self.writer().zerobreak()?;
-                self.writer().word(&cmnt.lines[0])?;
+                self.writer().word(cmnt.lines[0].clone())?;
                 self.writer().zerobreak()
             }
             comments::Isolated => {
@@ -548,7 +549,7 @@ pub trait PrintState<'a> {
                     // Don't print empty lines because they will end up as trailing
                     // whitespace
                     if !line.is_empty() {
-                        self.writer().word(&line[..])?;
+                        self.writer().word(line.clone())?;
                     }
                     self.writer().hardbreak()?;
                 }
@@ -559,13 +560,13 @@ pub trait PrintState<'a> {
                     self.writer().word(" ")?;
                 }
                 if cmnt.lines.len() == 1 {
-                    self.writer().word(&cmnt.lines[0])?;
+                    self.writer().word(cmnt.lines[0].clone())?;
                     self.writer().hardbreak()
                 } else {
                     self.ibox(0)?;
                     for line in &cmnt.lines {
                         if !line.is_empty() {
-                            self.writer().word(&line[..])?;
+                            self.writer().word(line.clone())?;
                         }
                         self.writer().hardbreak()?;
                     }
@@ -610,7 +611,7 @@ pub trait PrintState<'a> {
     fn print_literal(&mut self, lit: &ast::Lit) -> io::Result<()> {
         self.maybe_print_comment(lit.span.lo())?;
         if let Some(ltrl) = self.next_lit(lit.span.lo()) {
-            return self.writer().word(&ltrl.lit);
+            return self.writer().word(ltrl.lit.clone());
         }
         match lit.node {
             ast::LitKind::Str(st, style) => self.print_string(&st.as_str(), style),
@@ -618,31 +619,31 @@ pub trait PrintState<'a> {
                 let mut res = String::from("b'");
                 res.extend(ascii::escape_default(byte).map(|c| c as char));
                 res.push('\'');
-                self.writer().word(&res[..])
+                self.writer().word(res)
             }
             ast::LitKind::Char(ch) => {
                 let mut res = String::from("'");
                 res.extend(ch.escape_default());
                 res.push('\'');
-                self.writer().word(&res[..])
+                self.writer().word(res)
             }
             ast::LitKind::Int(i, t) => {
                 match t {
                     ast::LitIntType::Signed(st) => {
-                        self.writer().word(&st.val_to_string(i as i128))
+                        self.writer().word(st.val_to_string(i as i128))
                     }
                     ast::LitIntType::Unsigned(ut) => {
-                        self.writer().word(&ut.val_to_string(i))
+                        self.writer().word(ut.val_to_string(i))
                     }
                     ast::LitIntType::Unsuffixed => {
-                        self.writer().word(&i.to_string())
+                        self.writer().word(i.to_string())
                     }
                 }
             }
             ast::LitKind::Float(ref f, t) => {
-                self.writer().word(&format!("{}{}", &f, t.ty_to_string()))
+                self.writer().word(format!("{}{}", &f, t.ty_to_string()))
             }
-            ast::LitKind::FloatUnsuffixed(ref f) => self.writer().word(&f.as_str()),
+            ast::LitKind::FloatUnsuffixed(ref f) => self.writer().word(f.as_str().get()),
             ast::LitKind::Bool(val) => {
                 if val { self.writer().word("true") } else { self.writer().word("false") }
             }
@@ -652,7 +653,7 @@ pub trait PrintState<'a> {
                     escaped.extend(ascii::escape_default(ch)
                                          .map(|c| c as char));
                 }
-                self.writer().word(&format!("b\"{}\"", escaped))
+                self.writer().word(format!("b\"{}\"", escaped))
             }
         }
     }
@@ -669,7 +670,7 @@ pub trait PrintState<'a> {
                          string=st))
             }
         };
-        self.writer().word(&st[..])
+        self.writer().word(st)
     }
 
     fn print_inner_attributes(&mut self,
@@ -727,7 +728,7 @@ pub trait PrintState<'a> {
             if segment.ident.name != keywords::CrateRoot.name() &&
                segment.ident.name != keywords::DollarCrate.name()
             {
-                self.writer().word(&segment.ident.as_str())?;
+                self.writer().word(segment.ident.as_str().get())?;
             } else if segment.ident.name == keywords::DollarCrate.name() {
                 self.print_dollar_crate(segment.ident.span.ctxt())?;
             }
@@ -746,7 +747,7 @@ pub trait PrintState<'a> {
         }
         self.maybe_print_comment(attr.span.lo())?;
         if attr.is_sugared_doc {
-            self.writer().word(&attr.value_str().unwrap().as_str())?;
+            self.writer().word(attr.value_str().unwrap().as_str().get())?;
             self.writer().hardbreak()
         } else {
             match attr.style {
@@ -807,7 +808,7 @@ pub trait PrintState<'a> {
     fn print_tt(&mut self, tt: tokenstream::TokenTree) -> io::Result<()> {
         match tt {
             TokenTree::Token(_, ref tk) => {
-                self.writer().word(&token_to_string(tk))?;
+                self.writer().word(token_to_string(tk))?;
                 match *tk {
                     parse::token::DocComment(..) => {
                         self.writer().hardbreak()
@@ -816,11 +817,11 @@ pub trait PrintState<'a> {
                 }
             }
             TokenTree::Delimited(_, ref delimed) => {
-                self.writer().word(&token_to_string(&delimed.open_token()))?;
+                self.writer().word(token_to_string(&delimed.open_token()))?;
                 self.writer().space()?;
                 self.print_tts(delimed.stream())?;
                 self.writer().space()?;
-                self.writer().word(&token_to_string(&delimed.close_token()))
+                self.writer().word(token_to_string(&delimed.close_token()))
             },
         }
     }
@@ -889,12 +890,13 @@ impl<'a> State<'a> {
         self.s.cbox(u)
     }
 
-    pub fn word_nbsp(&mut self, w: &str) -> io::Result<()> {
+    pub fn word_nbsp<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
         self.s.word(w)?;
         self.nbsp()
     }
 
-    pub fn head(&mut self, w: &str) -> io::Result<()> {
+    pub fn head<S: Into<Cow<'static, str>>>(&mut self, w: S) -> io::Result<()> {
+        let w = w.into();
         // outer-box is consistent
         self.cbox(INDENT_UNIT)?;
         // head-box is inconsistent
@@ -956,7 +958,7 @@ impl<'a> State<'a> {
     pub fn synth_comment(&mut self, text: String) -> io::Result<()> {
         self.s.word("/*")?;
         self.s.space()?;
-        self.s.word(&text[..])?;
+        self.s.word(text)?;
         self.s.space()?;
         self.s.word("*/")
     }
@@ -1129,7 +1131,7 @@ impl<'a> State<'a> {
                 self.end() // end the outer fn box
             }
             ast::ForeignItemKind::Static(ref t, m) => {
-                self.head(&visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"))?;
                 if m {
                     self.word_space("mut")?;
                 }
@@ -1141,7 +1143,7 @@ impl<'a> State<'a> {
                 self.end() // end the outer cbox
             }
             ast::ForeignItemKind::Ty => {
-                self.head(&visibility_qualified(&item.vis, "type"))?;
+                self.head(visibility_qualified(&item.vis, "type"))?;
                 self.print_ident(item.ident)?;
                 self.s.word(";")?;
                 self.end()?; // end the head-ibox
@@ -1164,7 +1166,7 @@ impl<'a> State<'a> {
                               vis: &ast::Visibility)
                               -> io::Result<()>
     {
-        self.s.word(&visibility_qualified(vis, ""))?;
+        self.s.word(visibility_qualified(vis, ""))?;
         self.word_space("const")?;
         self.print_ident(ident)?;
         self.word_space(":")?;
@@ -1203,7 +1205,7 @@ impl<'a> State<'a> {
         self.ann.pre(self, AnnNode::Item(item))?;
         match item.node {
             ast::ItemKind::ExternCrate(orig_name) => {
-                self.head(&visibility_qualified(&item.vis, "extern crate"))?;
+                self.head(visibility_qualified(&item.vis, "extern crate"))?;
                 if let Some(orig_name) = orig_name {
                     self.print_name(orig_name)?;
                     self.s.space()?;
@@ -1216,14 +1218,14 @@ impl<'a> State<'a> {
                 self.end()?; // end outer head-block
             }
             ast::ItemKind::Use(ref tree) => {
-                self.head(&visibility_qualified(&item.vis, "use"))?;
+                self.head(visibility_qualified(&item.vis, "use"))?;
                 self.print_use_tree(tree)?;
                 self.s.word(";")?;
                 self.end()?; // end inner head-block
                 self.end()?; // end outer head-block
             }
             ast::ItemKind::Static(ref ty, m, ref expr) => {
-                self.head(&visibility_qualified(&item.vis, "static"))?;
+                self.head(visibility_qualified(&item.vis, "static"))?;
                 if m == ast::Mutability::Mutable {
                     self.word_space("mut")?;
                 }
@@ -1239,7 +1241,7 @@ impl<'a> State<'a> {
                 self.end()?; // end the outer cbox
             }
             ast::ItemKind::Const(ref ty, ref expr) => {
-                self.head(&visibility_qualified(&item.vis, "const"))?;
+                self.head(visibility_qualified(&item.vis, "const"))?;
                 self.print_ident(item.ident)?;
                 self.word_space(":")?;
                 self.print_type(ty)?;
@@ -1264,7 +1266,7 @@ impl<'a> State<'a> {
                 self.print_block_with_attrs(body, &item.attrs)?;
             }
             ast::ItemKind::Mod(ref _mod) => {
-                self.head(&visibility_qualified(&item.vis, "mod"))?;
+                self.head(visibility_qualified(&item.vis, "mod"))?;
                 self.print_ident(item.ident)?;
 
                 if _mod.inline || self.is_expanded {
@@ -1281,18 +1283,18 @@ impl<'a> State<'a> {
             }
             ast::ItemKind::ForeignMod(ref nmod) => {
                 self.head("extern")?;
-                self.word_nbsp(&nmod.abi.to_string())?;
+                self.word_nbsp(nmod.abi.to_string())?;
                 self.bopen()?;
                 self.print_foreign_mod(nmod, &item.attrs)?;
                 self.bclose(item.span)?;
             }
             ast::ItemKind::GlobalAsm(ref ga) => {
-                self.head(&visibility_qualified(&item.vis, "global_asm!"))?;
-                self.s.word(&ga.asm.as_str())?;
+                self.head(visibility_qualified(&item.vis, "global_asm!"))?;
+                self.s.word(ga.asm.as_str().get())?;
                 self.end()?;
             }
             ast::ItemKind::Ty(ref ty, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "type"))?;
+                self.head(visibility_qualified(&item.vis, "type"))?;
                 self.print_ident(item.ident)?;
                 self.print_generic_params(&generics.params)?;
                 self.end()?; // end the inner ibox
@@ -1305,7 +1307,7 @@ impl<'a> State<'a> {
                 self.end()?; // end the outer ibox
             }
             ast::ItemKind::Existential(ref bounds, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "existential type"))?;
+                self.head(visibility_qualified(&item.vis, "existential type"))?;
                 self.print_ident(item.ident)?;
                 self.print_generic_params(&generics.params)?;
                 self.end()?; // end the inner ibox
@@ -1326,11 +1328,11 @@ impl<'a> State<'a> {
                 )?;
             }
             ast::ItemKind::Struct(ref struct_def, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "struct"))?;
+                self.head(visibility_qualified(&item.vis, "struct"))?;
                 self.print_struct(struct_def, generics, item.ident, item.span, true)?;
             }
             ast::ItemKind::Union(ref struct_def, ref generics) => {
-                self.head(&visibility_qualified(&item.vis, "union"))?;
+                self.head(visibility_qualified(&item.vis, "union"))?;
                 self.print_struct(struct_def, generics, item.ident, item.span, true)?;
             }
             ast::ItemKind::Impl(unsafety,
@@ -1479,7 +1481,7 @@ impl<'a> State<'a> {
                           generics: &ast::Generics, ident: ast::Ident,
                           span: syntax_pos::Span,
                           visibility: &ast::Visibility) -> io::Result<()> {
-        self.head(&visibility_qualified(visibility, "enum"))?;
+        self.head(visibility_qualified(visibility, "enum"))?;
         self.print_ident(ident)?;
         self.print_generic_params(&generics.params)?;
         self.print_where_clause(&generics.where_clause)?;
@@ -1514,9 +1516,9 @@ impl<'a> State<'a> {
             ast::VisibilityKind::Restricted { ref path, .. } => {
                 let path = to_string(|s| s.print_path(path, false, 0));
                 if path == "self" || path == "super" {
-                    self.word_nbsp(&format!("pub({})", path))
+                    self.word_nbsp(format!("pub({})", path))
                 } else {
-                    self.word_nbsp(&format!("pub(in {})", path))
+                    self.word_nbsp(format!("pub(in {})", path))
                 }
             }
             ast::VisibilityKind::Inherited => Ok(())
@@ -2415,19 +2417,19 @@ impl<'a> State<'a> {
 
     pub fn print_ident(&mut self, ident: ast::Ident) -> io::Result<()> {
         if ident.is_raw_guess() {
-            self.s.word(&format!("r#{}", ident))?;
+            self.s.word(format!("r#{}", ident))?;
         } else {
-            self.s.word(&ident.as_str())?;
+            self.s.word(ident.as_str().get())?;
         }
         self.ann.post(self, AnnNode::Ident(&ident))
     }
 
     pub fn print_usize(&mut self, i: usize) -> io::Result<()> {
-        self.s.word(&i.to_string())
+        self.s.word(i.to_string())
     }
 
     pub fn print_name(&mut self, name: ast::Name) -> io::Result<()> {
-        self.s.word(&name.as_str())?;
+        self.s.word(name.as_str().get())?;
         self.ann.post(self, AnnNode::Name(&name))
     }
 
@@ -2851,10 +2853,8 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_type_bounds(&mut self,
-                        prefix: &str,
-                        bounds: &[ast::GenericBound])
-                        -> io::Result<()> {
+    pub fn print_type_bounds(&mut self, prefix: &'static str, bounds: &[ast::GenericBound])
+                             -> io::Result<()> {
         if !bounds.is_empty() {
             self.s.word(prefix)?;
             let mut first = true;
@@ -3146,7 +3146,7 @@ impl<'a> State<'a> {
             Some(Abi::Rust) => Ok(()),
             Some(abi) => {
                 self.word_nbsp("extern")?;
-                self.word_nbsp(&abi.to_string())
+                self.word_nbsp(abi.to_string())
             }
             None => Ok(())
         }
@@ -3157,7 +3157,7 @@ impl<'a> State<'a> {
         match opt_abi {
             Some(abi) => {
                 self.word_nbsp("extern")?;
-                self.word_nbsp(&abi.to_string())
+                self.word_nbsp(abi.to_string())
             }
             None => Ok(())
         }
@@ -3166,7 +3166,7 @@ impl<'a> State<'a> {
     pub fn print_fn_header_info(&mut self,
                                 header: ast::FnHeader,
                                 vis: &ast::Visibility) -> io::Result<()> {
-        self.s.word(&visibility_qualified(vis, ""))?;
+        self.s.word(visibility_qualified(vis, ""))?;
 
         match header.constness.node {
             ast::Constness::NotConst => {}
@@ -3178,7 +3178,7 @@ impl<'a> State<'a> {
 
         if header.abi != Abi::Rust {
             self.word_nbsp("extern")?;
-            self.word_nbsp(&header.abi.to_string())?;
+            self.word_nbsp(header.abi.to_string())?;
         }
 
         self.s.word("fn")
diff --git a/src/libsyntax_pos/symbol.rs b/src/libsyntax_pos/symbol.rs
index 361353c82e2..b891cdefc2a 100644
--- a/src/libsyntax_pos/symbol.rs
+++ b/src/libsyntax_pos/symbol.rs
@@ -493,6 +493,10 @@ impl LocalInternedString {
             symbol: Symbol::intern(self.string)
         }
     }
+
+    pub fn get(&self) -> &'static str {
+        self.string
+    }
 }
 
 impl<U: ?Sized> ::std::convert::AsRef<U> for LocalInternedString