fix review

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -2372,7 +2372,7 @@ fn compute_type_parameters(cx: &CodegenCx<'ll, 'tcx>, ty: Ty<'tcx>) -> &'ll DIAr
     fn get_parameter_names(cx: &CodegenCx<'_, '_>, generics: &ty::Generics) -> Vec<Symbol> {
         let mut names = generics
             .parent
-            .map_or_else(|| vec![], |def_id| get_parameter_names(cx, cx.tcx.generics_of(def_id)));
+            .map_or_else(Vec::new, |def_id| get_parameter_names(cx, cx.tcx.generics_of(def_id)));
         names.extend(generics.params.iter().map(|param| param.name));
         names
     }

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -481,10 +481,9 @@ impl DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
 
         fn get_parameter_names(cx: &CodegenCx<'_, '_>, generics: &ty::Generics) -> Vec<Symbol> {
-            let mut names = generics.parent.map_or_else(
+            let mut names = generics.parent.map_or_else(Vec::new, |def_id| {
-                || vec![],
+                get_parameter_names(cx, cx.tcx.generics_of(def_id))
-                |def_id| get_parameter_names(cx, cx.tcx.generics_of(def_id)),
+            });
-            );
             names.extend(generics.params.iter().map(|param| param.name));
             names
         }

compiler/rustc_codegen_llvm/src/metadata.rs

@@ -66,7 +66,7 @@ fn search_meta_section<'a>(
             let mut name_buf = None;
             let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
             let name = name_buf.map_or_else(
-                || String::new(), // We got a NULL ptr, ignore `name_len`.
+                String::new, // We got a NULL ptr, ignore `name_len`.
                 |buf| {
                     String::from_utf8(
                         slice::from_raw_parts(buf.as_ptr() as *const u8, name_len as usize)

compiler/rustc_mir/src/const_eval/eval_queries.rs

@@ -50,7 +50,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
 
     let name =
         with_no_trimmed_paths(|| ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id())));
-    let prom = cid.promoted.map_or_else(|| String::new(), |p| format!("::promoted[{:?}]", p));
+    let prom = cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p));
     trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
 
     ecx.push_stack_frame(

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -223,7 +223,7 @@ impl<'a> Parser<'a> {
         fn tokens_to_string(tokens: &[TokenType]) -> String {
             let mut i = tokens.iter();
             // This might be a sign we need a connect method on `Iterator`.
-            let b = i.next().map_or_else(|| String::new(), |t| t.to_string());
+            let b = i.next().map_or_else(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 ");

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1971,9 +1971,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
         // Therefore, we would compute `object_lifetime_defaults` to a
         // vector like `['x, 'static]`. Note that the vector only
         // includes type parameters.
-        let object_lifetime_defaults = type_def_id.map_or_else(
+        let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
-            || vec![],
-            |def_id| {
             let in_body = {
                 let mut scope = self.scope;
                 loop {
@@ -2031,8 +2029,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
                     Set1::Many => None,
                 })
                 .collect()
-            },
+        });
-        );
 
         debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
 

compiler/rustc_session/src/filesearch.rs

@@ -169,7 +169,7 @@ pub fn get_or_default_sysroot() -> PathBuf {
 
     // Check if sysroot is found using env::args().next(), and if is not found,
     // use env::current_exe() to imply sysroot.
-    from_env_args_next().unwrap_or_else(|| from_current_exe())
+    from_env_args_next().unwrap_or_else(from_current_exe)
 }
 
 // The name of the directory rustc expects libraries to be located.

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -349,7 +349,7 @@ fn report_negative_positive_conflict(
         E0751,
         "found both positive and negative implementation of trait `{}`{}:",
         overlap.trait_desc,
-        overlap.self_desc.clone().map_or_else(|| String::new(), |ty| format!(" for type `{}`", ty))
+        overlap.self_desc.clone().map_or_else(String::new, |ty| format!(" for type `{}`", ty))
     );
 
     match tcx.span_of_impl(negative_impl_def_id) {
@@ -400,7 +400,7 @@ fn report_conflicting_impls(
             overlap
                 .self_desc
                 .clone()
-                .map_or_else(|| String::new(), |ty| { format!(" for type `{}`", ty) }),
+                .map_or_else(String::new, |ty| { format!(" for type `{}`", ty) }),
             match used_to_be_allowed {
                 Some(FutureCompatOverlapErrorKind::Issue33140) => " (E0119)",
                 _ => "",
@@ -418,9 +418,7 @@ fn report_conflicting_impls(
                     impl_span,
                     format!(
                         "conflicting implementation{}",
-                        overlap
+                        overlap.self_desc.map_or_else(String::new, |ty| format!(" for `{}`", ty))
-                            .self_desc
-                            .map_or_else(|| String::new(), |ty| format!(" for `{}`", ty))
                     ),
                 );
             }

compiler/rustc_typeck/src/check/method/probe.rs

@@ -1695,7 +1695,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             } else {
                 self.fcx
                     .associated_item(def_id, name, Namespace::ValueNS)
-                    .map_or_else(|| Vec::new(), |x| vec![x])
+                    .map_or_else(Vec::new, |x| vec![x])
             }
         } else {
             self.tcx.associated_items(def_id).in_definition_order().copied().collect()