Rollup merge of #53563 - matthiaskrgr:String, r=varkor

use String::new() instead of String::from(""), "".to_string(), "".to_owned() or "".into()

src/librustc/infer/error_reporting/mod.rs

@@ -1330,7 +1330,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             s
         };
         let var_description = match var_origin {
-            infer::MiscVariable(_) => "".to_string(),
+            infer::MiscVariable(_) => String::new(),
             infer::PatternRegion(_) => " for pattern".to_string(),
             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
             infer::Autoref(_) => " for autoref".to_string(),

src/librustc/mir/mod.rs

@@ -2105,7 +2105,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                     region
                 } else {
                     // Do not even print 'static
-                    "".to_owned()
+                    String::new()
                 };
                 write!(fmt, "&{}{}{:?}", region, kind_str, place)
             }

src/librustc/session/config.rs

@@ -1051,7 +1051,7 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
         "perform LLVM link-time optimizations"),
     target_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
         "select target processor (rustc --print target-cpus for details)"),
-    target_feature: String = ("".to_string(), parse_string, [TRACKED],
+    target_feature: String = (String::new(), parse_string, [TRACKED],
         "target specific attributes (rustc --print target-features for details)"),
     passes: Vec<String> = (Vec::new(), parse_list, [TRACKED],
         "a list of extra LLVM passes to run (space separated)"),
@@ -1085,7 +1085,7 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
          "choose the code model to use (rustc --print code-models for details)"),
     metadata: Vec<String> = (Vec::new(), parse_list, [TRACKED],
          "metadata to mangle symbol names with"),
-    extra_filename: String = ("".to_string(), parse_string, [UNTRACKED],
+    extra_filename: String = (String::new(), parse_string, [UNTRACKED],
          "extra data to put in each output filename"),
     codegen_units: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
         "divide crate into N units to optimize in parallel"),
@@ -1992,7 +1992,7 @@ pub fn build_session_options_and_crate_config(
     };
     if cg.target_feature == "help" {
         prints.push(PrintRequest::TargetFeatures);
-        cg.target_feature = "".to_string();
+        cg.target_feature = String::new();
     }
     if cg.relocation_model.as_ref().map_or(false, |s| s == "help") {
         prints.push(PrintRequest::RelocationModels);

src/librustc/traits/error_reporting.rs

@@ -472,7 +472,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                           if len > 5 {
                               format!("\nand {} others", len - 4)
                           } else {
-                              "".to_owned()
+                              String::new()
                           }
                           ));
     }
@@ -917,7 +917,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                                  remove_refs);
 
                         err.span_suggestion_short_with_applicability(
-                            sp, &format_str, String::from(""), Applicability::MachineApplicable
+                            sp, &format_str, String::new(), Applicability::MachineApplicable
                         );
                         break;
                     }
@@ -1116,7 +1116,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                         .collect::<Vec<String>>()
                                         .join(", "))
                         } else {
-                            "".to_owned()
+                            String::new()
                         },
                     );
                     err.span_suggestion_with_applicability(

src/librustc/traits/select.rs

@@ -120,13 +120,13 @@ impl IntercrateAmbiguityCause {
             &IntercrateAmbiguityCause::DownstreamCrate { ref trait_desc, ref self_desc } => {
                 let self_desc = if let &Some(ref ty) = self_desc {
                     format!(" for type `{}`", ty)
-                } else { "".to_string() };
+                } else { String::new() };
                 format!("downstream crates may implement trait `{}`{}", trait_desc, self_desc)
             }
             &IntercrateAmbiguityCause::UpstreamCrateUpdate { ref trait_desc, ref self_desc } => {
                 let self_desc = if let &Some(ref ty) = self_desc {
                     format!(" for type `{}`", ty)
-                } else { "".to_string() };
+                } else { String::new() };
                 format!("upstream crates may add new impl of trait `{}`{} \
                          in future versions",
                         trait_desc, self_desc)

src/librustc/util/common.rs

@@ -213,7 +213,7 @@ fn print_time_passes_entry_internal(what: &str, dur: Duration) {
             let mb = n as f64 / 1_000_000.0;
             format!("; rss: {}MB", mb.round() as usize)
         }
-        None => "".to_owned(),
+        None => String::new(),
     };
     println!("{}time: {}{}\t{}",
              "  ".repeat(indentation),

src/librustc/util/profiling.rs

@@ -73,7 +73,7 @@ macro_rules! define_categories {
                         (format!("{:.2}",
                         (((hits as f32) / (total as f32)) * 100.0)), total.to_string())
                     } else {
-                        ("".into(), "".into())
+                        (String::new(), String::new())
                     };
 
                     writeln!(

src/librustc_borrowck/borrowck/unused.rs

@@ -87,7 +87,7 @@ impl<'a, 'tcx> UnusedMutCx<'a, 'tcx> {
                 .span_suggestion_short_with_applicability(
                     mut_span,
                     "remove this `mut`",
-                    "".to_owned(),
+                    String::new(),
                     Applicability::MachineApplicable)
                 .emit();
         }

src/librustc_borrowck/dataflow.rs

@@ -140,21 +140,21 @@ impl<'a, 'tcx, O:DataFlowOperator> pprust::PpAnn for DataFlowContext<'a, 'tcx, O
             let gens_str = if gens.iter().any(|&u| u != 0) {
                 format!(" gen: {}", bits_to_string(gens))
             } else {
-                "".to_string()
+                String::new()
             };
 
             let action_kills = &self.action_kills[start .. end];
             let action_kills_str = if action_kills.iter().any(|&u| u != 0) {
                 format!(" action_kill: {}", bits_to_string(action_kills))
             } else {
-                "".to_string()
+                String::new()
             };
 
             let scope_kills = &self.scope_kills[start .. end];
             let scope_kills_str = if scope_kills.iter().any(|&u| u != 0) {
                 format!(" scope_kill: {}", bits_to_string(scope_kills))
             } else {
-                "".to_string()
+                String::new()
             };
 
             ps.synth_comment(

src/librustc_borrowck/graphviz.rs

@@ -53,7 +53,7 @@ impl<'a, 'tcx> DataflowLabeller<'a, 'tcx> {
     fn dataflow_for(&self, e: EntryOrExit, n: &Node<'a>) -> String {
         let id = n.1.data.id();
         debug!("dataflow_for({:?}, id={:?}) {:?}", e, id, self.variants);
-        let mut sets = "".to_string();
+        let mut sets = String::new();
         let mut seen_one = false;
         for &variant in &self.variants {
             if seen_one { sets.push_str(" "); } else { seen_one = true; }

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -1191,7 +1191,7 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                                               member_descriptions);
                 vec![
                     MemberDescription {
-                        name: "".to_string(),
+                        name: String::new(),
                         type_metadata: variant_type_metadata,
                         offset: Size::ZERO,
                         size: self.layout.size,
@@ -1220,7 +1220,7 @@ impl EnumMemberDescriptionFactory<'ll, 'tcx> {
                                                   variant_type_metadata,
                                                   member_descriptions);
                     MemberDescription {
-                        name: "".to_string(),
+                        name: String::new(),
                         type_metadata: variant_type_metadata,
                         offset: Size::ZERO,
                         size: variant.size,

src/librustc_driver/profile/trace.rs

@@ -85,7 +85,7 @@ pub fn html_of_effect(eff: &Effect) -> (String, String) {
 fn html_of_duration(_start: &Instant, dur: &Duration) -> (String, String) {
     use rustc::util::common::duration_to_secs_str;
     (duration_to_secs_str(dur.clone()),
-     "".to_string()
+     String::new()
     )
 }
 

src/librustc_errors/emitter.rs

@@ -798,7 +798,7 @@ impl EmitterWriter {
                                                          // at by "in this macro invocation"
                                                          format!(" (#{})", i + 1)
                                                      } else {
-                                                         "".to_string()
+                                                         String::new()
                                                      })));
                         }
                         // Check to make sure we're not in any <*macros>
@@ -813,7 +813,7 @@ impl EmitterWriter {
                                                          // backtrace is multiple levels deep
                                                          format!(" (#{})", i + 1)
                                                      } else {
-                                                         "".to_string()
+                                                         String::new()
                                                      })));
                             if !always_backtrace {
                                 break;
@@ -1065,7 +1065,7 @@ impl EmitterWriter {
                     let col = if let Some(first_annotation) = first_line.annotations.first() {
                         format!(":{}", first_annotation.start_col + 1)
                     } else {
-                        "".to_string()
+                        String::new()
                     };
                     format!("{}:{}{}",
                             annotated_file.file.name,

src/librustc_lint/builtin.rs

@@ -795,7 +795,7 @@ impl EarlyLintPass for DeprecatedAttr {
                     err.span_suggestion_short_with_applicability(
                         attr.span,
                         "remove this attribute",
-                        "".to_owned(),
+                        String::new(),
                         Applicability::MachineApplicable
                     );
                     err.emit();
@@ -1251,7 +1251,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
                                 err.span_suggestion_short_with_applicability(
                                     no_mangle_attr.span,
                                     "remove this attribute",
-                                    "".to_owned(),
+                                    String::new(),
                                     // Use of `#[no_mangle]` suggests FFI intent; correct
                                     // fix may be to monomorphize source by hand
                                     Applicability::MaybeIncorrect

src/librustc_mir/borrow_check/mod.rs

@@ -327,7 +327,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
             err.span_suggestion_short_with_applicability(
                 mut_span,
                 "remove this `mut`",
-                "".to_owned(),
+                String::new(),
                 Applicability::MachineApplicable);
 
             err.buffer(&mut mbcx.errors_buffer);

src/librustc_mir/borrow_check/mutability_errors.rs

@@ -128,7 +128,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
                         }
                     } else {
                         item_msg = format!("data in a {}", pointer_type);
-                        reason = "".to_string();
+                        reason = String::new();
                     }
                 }
             }
@@ -138,7 +138,7 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
             Place::Static(box Static { def_id, ty: _ }) => {
                 if let Place::Static(_) = access_place {
                     item_msg = format!("immutable static item `{}`", access_place_desc.unwrap());
-                    reason = "".to_string();
+                    reason = String::new();
                 } else {
                     item_msg = format!("`{}`", access_place_desc.unwrap());
                     let static_name = &self.tcx.item_name(*def_id);

src/librustc_mir/util/borrowck_errors.rs

@@ -474,7 +474,7 @@ pub trait BorrowckErrors<'cx>: Sized + Copy {
     ) -> DiagnosticBuilder<'cx> {
         let moved_path = moved_path
             .map(|mp| format!(": `{}`", mp))
-            .unwrap_or("".to_owned());
+            .unwrap_or(String::new());
 
         let err = struct_span_err!(
             self,

src/librustc_resolve/resolve_imports.rs

@@ -994,7 +994,7 @@ impl<'a, 'b:'a, 'c: 'b> ImportResolver<'a, 'b, 'c> {
                 let lev_suggestion =
                     match find_best_match_for_name(names, &ident.as_str(), None) {
                         Some(name) => format!(". Did you mean to use `{}`?", name),
-                        None => "".to_owned(),
+                        None => String::new(),
                     };
                 let msg = match module {
                     ModuleOrUniformRoot::Module(module) => {

src/librustc_save_analysis/lib.rs

@@ -1050,7 +1050,7 @@ impl<'a> DumpHandler<'a> {
                     .iter()
                     .any(|ct| *ct == CrateType::Executable);
                 let mut out_name = if executable {
-                    "".to_owned()
+                    String::new()
                 } else {
                     "lib".to_owned()
                 };

src/librustc_target/spec/aarch64_apple_ios.rs

@@ -21,7 +21,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "ios".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/aarch64_fuchsia.rs

@@ -22,8 +22,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "fuchsia".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             abi_blacklist: super::arm_base::abi_blacklist(),

src/librustc_target/spec/aarch64_linux_android.rs

@@ -27,7 +27,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "android".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/aarch64_unknown_cloudabi.rs

@@ -24,7 +24,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "cloudabi".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/aarch64_unknown_freebsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "freebsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/aarch64_unknown_hermit.rs

@@ -24,7 +24,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "hermit".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/aarch64_unknown_netbsd.rs

@@ -23,7 +23,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/aarch64_unknown_none.rs

@@ -36,8 +36,8 @@ pub fn target() -> Result<Target, String> {
         target_pointer_width: "64".to_string(),
         target_c_int_width: "32".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),

src/librustc_target/spec/aarch64_unknown_openbsd.rs

@@ -23,7 +23,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
         target_os: "openbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/arm_linux_androideabi.rs

@@ -24,7 +24,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "android".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/armebv7r_none_eabihf.rs

@@ -22,8 +22,8 @@ pub fn target() -> TargetResult {
         data_layout: "E-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/armv7_apple_ios.rs

@@ -21,7 +21,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/armv7_linux_androideabi.rs

@@ -28,7 +28,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "android".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/armv7_unknown_cloudabi_eabihf.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "cloudabi".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/armv7s_apple_ios.rs

@@ -21,7 +21,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32".to_string(),
         arch: "arm".to_string(),
         target_os: "ios".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/asmjs_unknown_emscripten.rs

@@ -40,7 +40,7 @@ pub fn target() -> Result<Target, String> {
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         data_layout: "e-p:32:32-i64:64-v128:32:128-n32-S128".to_string(),
         arch: "asmjs".to_string(),

src/librustc_target/spec/i386_apple_ios.rs

@@ -21,7 +21,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "ios".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/i686_apple_darwin.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "macos".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_linux_android.rs

@@ -31,7 +31,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "android".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_cloudabi.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "cloudabi".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_dragonfly.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "dragonfly".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_freebsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "freebsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_haiku.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "haiku".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_netbsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/i686_unknown_openbsd.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128".to_string(),
         arch: "x86".to_string(),
         target_os: "openbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/mod.rs

@@ -686,7 +686,7 @@ impl Default for TargetOptions {
             post_link_args: LinkArgs::new(),
             asm_args: Vec::new(),
             cpu: "generic".to_string(),
-            features: "".to_string(),
+            features: String::new(),
             dynamic_linking: false,
             only_cdylib: false,
             executables: false,
@@ -698,7 +698,7 @@ impl Default for TargetOptions {
             function_sections: true,
             dll_prefix: "lib".to_string(),
             dll_suffix: ".so".to_string(),
-            exe_suffix: "".to_string(),
+            exe_suffix: String::new(),
             staticlib_prefix: "lib".to_string(),
             staticlib_suffix: ".a".to_string(),
             target_family: None,

src/librustc_target/spec/msp430_none_elf.rs

@@ -19,8 +19,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:16:16-i32:16-i64:16-f32:16-f64:16-a:8-n8:16-S16".to_string(),
         arch: "msp430".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/powerpc_unknown_netbsd.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "E-m:e-p:32:32-i64:64-n32".to_string(),
         arch: "powerpc".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/riscv32imac_unknown_none_elf.rs

@@ -19,7 +19,7 @@ pub fn target() -> TargetResult {
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         arch: "riscv32".to_string(),
         linker_flavor: LinkerFlavor::Ld,

src/librustc_target/spec/sparc64_unknown_netbsd.rs

@@ -24,7 +24,7 @@ pub fn target() -> TargetResult {
         data_layout: "E-m:e-i64:64-n32:64-S128".to_string(),
         arch: "sparc64".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/sparcv9_sun_solaris.rs

@@ -30,7 +30,7 @@ pub fn target() -> TargetResult {
         // just be confusing.
         arch: "sparc64".to_string(),
         target_os: "solaris".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "sun".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/thumbv6m_none_eabi.rs

@@ -21,8 +21,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/thumbv7em_none_eabi.rs

@@ -30,8 +30,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/thumbv7em_none_eabihf.rs

@@ -29,8 +29,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/thumbv7m_none_eabi.rs

@@ -21,8 +21,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64".to_string(),
         arch: "arm".to_string(),
         target_os: "none".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
 
         options: TargetOptions {

src/librustc_target/spec/wasm32_experimental_emscripten.rs

@@ -43,7 +43,7 @@ pub fn target() -> Result<Target, String> {
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-n32:64-S128".to_string(),
         arch: "wasm32".to_string(),

src/librustc_target/spec/wasm32_unknown_emscripten.rs

@@ -40,7 +40,7 @@ pub fn target() -> Result<Target, String> {
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),
         target_os: "emscripten".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         data_layout: "e-p:32:32-i64:64-v128:32:128-n32-S128".to_string(),
         arch: "wasm32".to_string(),

src/librustc_target/spec/wasm32_unknown_unknown.rs

@@ -32,7 +32,7 @@ pub fn target() -> Result<Target, String> {
 
         // relatively self-explanatory!
         exe_suffix: ".wasm".to_string(),
-        dll_prefix: "".to_string(),
+        dll_prefix: String::new(),
         dll_suffix: ".wasm".to_string(),
         linker_is_gnu: false,
 
@@ -65,7 +65,7 @@ pub fn target() -> Result<Target, String> {
         // This is basically guaranteed to change in the future, don't rely on
         // this. Use `not(target_os = "emscripten")` for now.
         target_os: "unknown".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         data_layout: "e-m:e-p:32:32-i64:64-n32:64-S128".to_string(),
         arch: "wasm32".to_string(),

src/librustc_target/spec/windows_base.rs

@@ -77,10 +77,10 @@ pub fn opts() -> TargetOptions {
         linker: Some("gcc".to_string()),
         dynamic_linking: true,
         executables: true,
-        dll_prefix: "".to_string(),
+        dll_prefix: String::new(),
         dll_suffix: ".dll".to_string(),
         exe_suffix: ".exe".to_string(),
-        staticlib_prefix: "".to_string(),
+        staticlib_prefix: String::new(),
         staticlib_suffix: ".lib".to_string(),
         no_default_libraries: true,
         target_family: Some("windows".to_string()),

src/librustc_target/spec/windows_msvc_base.rs

@@ -21,10 +21,10 @@ pub fn opts() -> TargetOptions {
         function_sections: true,
         dynamic_linking: true,
         executables: true,
-        dll_prefix: "".to_string(),
+        dll_prefix: String::new(),
         dll_suffix: ".dll".to_string(),
         exe_suffix: ".exe".to_string(),
-        staticlib_prefix: "".to_string(),
+        staticlib_prefix: String::new(),
         staticlib_suffix: ".lib".to_string(),
         target_family: Some("windows".to_string()),
         is_like_windows: true,

src/librustc_target/spec/x86_64_apple_darwin.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "macos".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_apple_ios.rs

@@ -21,7 +21,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:o-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "ios".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "apple".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {

src/librustc_target/spec/x86_64_fuchsia.rs

@@ -25,8 +25,8 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "fuchsia".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
-        target_vendor: "".to_string(),
+        target_vendor: String::new(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,
     })

src/librustc_target/spec/x86_64_linux_android.rs

@@ -27,7 +27,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "android".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_rumprun_netbsd.rs

@@ -33,7 +33,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "rumprun".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_sun_solaris.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "solaris".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "sun".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_bitrig.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "bitrig".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_cloudabi.rs

@@ -26,7 +26,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "cloudabi".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_dragonfly.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "dragonfly".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_freebsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "freebsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_haiku.rs

@@ -27,7 +27,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "haiku".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_hermit.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "hermit".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_netbsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "netbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_openbsd.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "openbsd".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_target/spec/x86_64_unknown_redox.rs

@@ -25,7 +25,7 @@ pub fn target() -> TargetResult {
         data_layout: "e-m:e-i64:64-f80:128-n8:16:32:64-S128".to_string(),
         arch: "x86_64".to_string(),
         target_os: "redox".to_string(),
-        target_env: "".to_string(),
+        target_env: String::new(),
         target_vendor: "unknown".to_string(),
         linker_flavor: LinkerFlavor::Gcc,
         options: base,

src/librustc_typeck/check/mod.rs

@@ -3471,7 +3471,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             displayable_field_names.sort();
 
             let truncated_fields_error = if len <= 3 {
-                "".to_string()
+                String::new()
             } else {
                 format!(" and {} other field{}", (len - 3), if len - 3 == 1 {""} else {"s"})
             };
@@ -4783,7 +4783,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         err.span_suggestion_with_applicability(
             span_semi,
             "consider removing this semicolon",
-            "".to_string(),
+            String::new(),
             Applicability::MachineApplicable);
     }
 

src/librustc_typeck/check_unused.rs

@@ -142,7 +142,7 @@ fn unused_crates_lint<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) {
                 .span_suggestion_short_with_applicability(
                     span,
                     "remove it",
-                    "".to_string(),
+                    String::new(),
                     Applicability::MachineApplicable)
                 .emit();
             continue;

src/librustdoc/clean/mod.rs

@@ -568,7 +568,7 @@ impl Clean<Item> for doctree::Module {
         let name = if self.name.is_some() {
             self.name.expect("No name provided").clean(cx)
         } else {
-            "".to_string()
+            String::new()
         };
 
         // maintain a stack of mod ids, for doc comment path resolution
@@ -1760,7 +1760,7 @@ impl<'a, 'tcx> Clean<FnDecl> for (DefId, ty::PolyFnSig<'tcx>) {
                 values: sig.skip_binder().inputs().iter().map(|t| {
                     Argument {
                         type_: t.clean(cx),
-                        name: names.next().map_or("".to_string(), |name| name.to_string()),
+                        name: names.next().map_or(String::new(), |name| name.to_string()),
                     }
                 }).collect(),
             },
@@ -3596,7 +3596,7 @@ impl Clean<Item> for hir::ForeignItem {
                 ForeignStaticItem(Static {
                     type_: ty.clean(cx),
                     mutability: if mutbl {Mutable} else {Immutable},
-                    expr: "".to_string(),
+                    expr: String::new(),
                 })
             }
             hir::ForeignItemKind::Type => {
@@ -3628,7 +3628,7 @@ impl ToSource for syntax_pos::Span {
         debug!("converting span {:?} to snippet", self.clean(cx));
         let sn = match cx.sess().source_map().span_to_snippet(*self) {
             Ok(x) => x.to_string(),
-            Err(_) => "".to_string()
+            Err(_) => String::new()
         };
         debug!("got snippet {}", sn);
         sn
@@ -3824,19 +3824,19 @@ impl Clean<Stability> for attr::Stability {
             feature: self.feature.to_string(),
             since: match self.level {
                 attr::Stable {ref since} => since.to_string(),
-                _ => "".to_string(),
+                _ => String::new(),
             },
             deprecated_since: match self.rustc_depr {
                 Some(attr::RustcDeprecation {ref since, ..}) => since.to_string(),
-                _=> "".to_string(),
+                _=> String::new(),
             },
             deprecated_reason: match self.rustc_depr {
                 Some(ref depr) => depr.reason.to_string(),
-                _ => "".to_string(),
+                _ => String::new(),
             },
             unstable_reason: match self.level {
                 attr::Unstable { reason: Some(ref reason), .. } => reason.to_string(),
-                _ => "".to_string(),
+                _ => String::new(),
             },
             issue: match self.level {
                 attr::Unstable {issue, ..} => Some(issue),
@@ -3855,8 +3855,8 @@ impl<'a> Clean<Stability> for &'a attr::Stability {
 impl Clean<Deprecation> for attr::Deprecation {
     fn clean(&self, _: &DocContext) -> Deprecation {
         Deprecation {
-            since: self.since.as_ref().map_or("".to_string(), |s| s.to_string()),
+            since: self.since.as_ref().map_or(String::new(), |s| s.to_string()),
-            note: self.note.as_ref().map_or("".to_string(), |s| s.to_string()),
+            note: self.note.as_ref().map_or(String::new(), |s| s.to_string()),
         }
     }
 }

src/librustdoc/html/format.rs

@@ -620,7 +620,7 @@ fn fmt_type(t: &clean::Type, f: &mut fmt::Formatter, use_absolute: bool) -> fmt:
         clean::BorrowedRef{ lifetime: ref l, mutability, type_: ref ty} => {
             let lt = match *l {
                 Some(ref l) => format!("{} ", *l),
-                _ => "".to_string(),
+                _ => String::new(),
             };
             let m = MutableSpace(mutability);
             let amp = if f.alternate() {

src/librustdoc/html/layout.rs

@@ -156,13 +156,13 @@ pub fn render<T: fmt::Display, S: fmt::Display>(
                 root_path = page.root_path,
                 suffix=page.resource_suffix)
     } else {
-        "".to_owned()
+        String::new()
     },
     content   = *t,
     root_path = page.root_path,
     css_class = page.css_class,
     logo      = if layout.logo.is_empty() {
-        "".to_string()
+        String::new()
     } else {
         format!("<a href='{}{}/index.html'>\
                  <img src='{}' alt='logo' width='100'></a>",
@@ -173,7 +173,7 @@ pub fn render<T: fmt::Display, S: fmt::Display>(
     description = page.description,
     keywords = page.keywords,
     favicon   = if layout.favicon.is_empty() {
-        "".to_string()
+        String::new()
     } else {
         format!(r#"<link rel="shortcut icon" href="{}">"#, layout.favicon)
     },

src/librustdoc/html/render.rs

@@ -504,8 +504,8 @@ pub fn run(mut krate: clean::Crate,
         local_sources: FxHashMap(),
         issue_tracker_base_url: None,
         layout: layout::Layout {
-            logo: "".to_string(),
+            logo: String::new(),
-            favicon: "".to_string(),
+            favicon: String::new(),
             external_html: external_html.clone(),
             krate: krate.name.clone(),
         },
@@ -2183,7 +2183,7 @@ fn shorter<'a>(s: Option<&'a str>) -> String {
                 !chr.is_whitespace()
             })
         }).collect::<Vec<_>>().join("\n"),
-        None => "".to_string()
+        None => String::new()
     }
 }
 
@@ -2479,7 +2479,7 @@ fn item_module(w: &mut fmt::Formatter, cx: &Context,
                        stab_docs = stab_docs,
                        docs = MarkdownSummaryLine(doc_value, &myitem.links()),
                        class = myitem.type_(),
-                       stab = myitem.stability_class().unwrap_or("".to_string()),
+                       stab = myitem.stability_class().unwrap_or(String::new()),
                        unsafety_flag = unsafety_flag,
                        href = item_path(myitem.type_(), myitem.name.as_ref().unwrap()),
                        title_type = myitem.type_(),

src/libsyntax/ext/source_util.rs

@@ -184,7 +184,7 @@ pub fn expand_include_bytes(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::Toke
         Ok(..) => {
             // Add this input file to the code map to make it available as
             // dependency information, but don't enter it's contents
-            cx.source_map().new_source_file(file.into(), "".to_string());
+            cx.source_map().new_source_file(file.into(), String::new());
 
             base::MacEager::expr(cx.expr_lit(sp, ast::LitKind::ByteStr(Lrc::new(bytes))))
         }

src/libsyntax/parse/lexer/comments.rs

@@ -230,7 +230,7 @@ fn trim_whitespace_prefix_and_push_line(lines: &mut Vec<String>, s: String, col:
             if col < len {
                 (&s[col..len]).to_string()
             } else {
-                "".to_string()
+                String::new()
             }
         }
         None => s,

src/libsyntax/parse/parser.rs

@@ -684,7 +684,7 @@ impl<'a> Parser<'a> {
             let mut i = tokens.iter();
             // This might be a sign we need a connect method on Iterator.
             let b = i.next()
-                     .map_or("".to_string(), |t| t.to_string());
+                     .map_or(String::new(), |t| t.to_string());
             i.enumerate().fold(b, |mut b, (i, a)| {
                 if tokens.len() > 2 && i == tokens.len() - 2 {
                     b.push_str(", or ");
@@ -786,7 +786,7 @@ impl<'a> Parser<'a> {
         } else {
             err.span_label(self.span, "expected identifier");
             if self.token == token::Comma && self.look_ahead(1, |t| t.is_ident()) {
-                err.span_suggestion(self.span, "remove this comma", "".into());
+                err.span_suggestion(self.span, "remove this comma", String::new());
             }
         }
         err
@@ -2518,7 +2518,7 @@ impl<'a> Parser<'a> {
                     err.span_suggestion_short_with_applicability(
                         self.span,
                         "remove this comma",
-                        "".to_owned(),
+                        String::new(),
                         Applicability::MachineApplicable
                     );
                     err.note("the base struct must always be the last field");
@@ -3485,7 +3485,7 @@ impl<'a> Parser<'a> {
                 e.span_suggestion_short_with_applicability(
                     match_span,
                     "try removing this `match`",
-                    "".to_owned(),
+                    String::new(),
                     Applicability::MaybeIncorrect // speculative
                 );
             }
@@ -3862,7 +3862,7 @@ impl<'a> Parser<'a> {
                 if self.token == token::CloseDelim(token::Brace) {
                     // If the struct looks otherwise well formed, recover and continue.
                     if let Some(sp) = comma_sp {
-                        err.span_suggestion_short(sp, "remove this comma", "".into());
+                        err.span_suggestion_short(sp, "remove this comma", String::new());
                     }
                     err.emit();
                     break;
@@ -3902,7 +3902,7 @@ impl<'a> Parser<'a> {
                 err.multipart_suggestion(
                     "move the `..` to the end of the field list",
                     vec![
-                        (etc_span, "".into()),
+                        (etc_span, String::new()),
                         (self.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
                     ],
                 );
@@ -6210,7 +6210,7 @@ impl<'a> Parser<'a> {
             if token_str == ";" {
                 let msg = "consider removing this semicolon";
                 err.span_suggestion_short_with_applicability(
-                    self.span, msg, "".to_string(), Applicability::MachineApplicable
+                    self.span, msg, String::new(), Applicability::MachineApplicable
                 );
                 if !items.is_empty() {  // Issue #51603
                     let previous_item = &items[items.len()-1];

src/libsyntax/source_map.rs

@@ -1030,7 +1030,7 @@ mod tests {
         cm.new_source_file(PathBuf::from("blork.rs").into(),
                        "first line.\nsecond line".to_string());
         cm.new_source_file(PathBuf::from("empty.rs").into(),
-                       "".to_string());
+                       String::new());
         cm.new_source_file(PathBuf::from("blork2.rs").into(),
                        "first line.\nsecond line".to_string());
         cm

src/libtest/formatters/json.rs

@@ -102,7 +102,7 @@ impl<T: Write> OutputFormatter for JsonFormatter<T> {
                 let deviation = (bs.ns_iter_summ.max - bs.ns_iter_summ.min) as usize;
 
                 let mbps = if bs.mb_s == 0 {
-                    "".into()
+                    String::new()
                 } else {
                     format!(r#", "mib_per_second": {}"#, bs.mb_s)
                 };

src/tools/compiletest/src/header.rs

@@ -559,7 +559,7 @@ impl Config {
             let mut strs: Vec<String> = nv.splitn(2, '=').map(str::to_owned).collect();
 
             match strs.len() {
-                1 => (strs.pop().unwrap(), "".to_owned()),
+                1 => (strs.pop().unwrap(), String::new()),
                 2 => {
                     let end = strs.pop().unwrap();
                     (strs.pop().unwrap(), end)

src/tools/tidy/src/features.rs

@@ -252,7 +252,7 @@ pub fn collect_lib_features(base_src_path: &Path) -> Features {
     // add it to the set of known library features so we can still generate docs.
     lib_features.insert("compiler_builtins_lib".to_owned(), Feature {
         level: Status::Unstable,
-        since: "".to_owned(),
+        since: String::new(),
         has_gate_test: false,
         tracking_issue: None,
     });