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

Author: matthiaskrgr

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; }