Rollup merge of rust-lang#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_vendor: "".to_string(),
+        target_env: String::new(),
+        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_vendor: "".to_string(),
+        target_env: String::new(),
+        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_vendor: "".to_string(),
+        target_env: String::new(),
+        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 {