diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index c27b39a9d62ffbe2df1d4cb04492cc4e65d0c12e..2bce1ac3c0a216211d74aa95e5cef6750b2421dc 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -493,7 +493,7 @@ fn line_from_source_file(
         h_end: usize,
     ) -> DiagnosticSpanLine {
         DiagnosticSpanLine {
-            text: sf.get_line(index).map_or(String::new(), |l| l.into_owned()),
+            text: sf.get_line(index).map_or_else(String::new, |l| l.into_owned()),
             highlight_start: h_start,
             highlight_end: h_end,
         }
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index f61b6946985e5831f230a28bb273da7fd20e0e0c..a753c4ab6ce966fce9092f44c089547c9b753468 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -216,9 +216,10 @@ pub fn generates_cgu_internal_copy(&self, tcx: TyCtxt<'tcx>) -> bool {
             // drops of `Option::None` before LTO. We also respect the intent of
             // `#[inline]` on `Drop::drop` implementations.
             return ty.ty_adt_def().map_or(true, |adt_def| {
-                adt_def.destructor(tcx).map_or(adt_def.is_enum(), |dtor| {
-                    tcx.codegen_fn_attrs(dtor.did).requests_inline()
-                })
+                adt_def.destructor(tcx).map_or_else(
+                    || adt_def.is_enum(),
+                    |dtor| tcx.codegen_fn_attrs(dtor.did).requests_inline(),
+                )
             });
         }
         tcx.codegen_fn_attrs(self.def_id()).requests_inline()
diff --git a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs b/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
index ff11314d2ffd1c82e62ed6a08ae78b62cf8ce2d0..416199b384000e72d9498df7f2a054205c1aa4c0 100644
--- a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
+++ b/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
@@ -525,7 +525,7 @@ pub fn store_diagnostics_for_anon_node(
     ) {
         let mut current_diagnostics = self.current_diagnostics.borrow_mut();
 
-        let x = current_diagnostics.entry(dep_node_index).or_insert(Vec::new());
+        let x = current_diagnostics.entry(dep_node_index).or_default();
 
         x.extend(Into::<Vec<_>>::into(diagnostics));
     }
diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/outlives_suggestion.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/outlives_suggestion.rs
index 7505e6e2dd11e224db3f97f0c0b91372335ac407..3629c813bc7a05252a0b620a4eb2fb711d6299e9 100644
--- a/compiler/rustc_mir/src/borrow_check/diagnostics/outlives_suggestion.rs
+++ b/compiler/rustc_mir/src/borrow_check/diagnostics/outlives_suggestion.rs
@@ -157,7 +157,7 @@ fn compile_all_suggestions(
         debug!("Collected {:?}: {:?}", fr, outlived_fr);
 
         // Add to set of constraints for final help note.
-        self.constraints_to_add.entry(fr).or_insert(Vec::new()).push(outlived_fr);
+        self.constraints_to_add.entry(fr).or_default().push(outlived_fr);
     }
 
     /// Emit an intermediate note on the given `Diagnostic` if the involved regions are
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index f9f33492a1ec35d0e6584755056b33dc86729244..1377bb781d0086089efd4eec3539947b8e69d05d 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -2327,7 +2327,7 @@ fn resolve_expr(&mut self, expr: &'ast Expr, parent: Option<&'ast Expr>) {
 
             ExprKind::Call(ref callee, ref arguments) => {
                 self.resolve_expr(callee, Some(expr));
-                let const_args = self.r.legacy_const_generic_args(callee).unwrap_or(Vec::new());
+                let const_args = self.r.legacy_const_generic_args(callee).unwrap_or_default();
                 for (idx, argument) in arguments.iter().enumerate() {
                     // Constant arguments need to be treated as AnonConst since
                     // that is how they will be later lowered to HIR.
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index e85d78db22c563af4b9d7dd8ae4c405632ae06a8..4c0df2701f5e302303c869ef8008eda21647747c 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -184,7 +184,7 @@ pub(crate) fn smart_resolve_report_errors(
                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
                         _ => None,
                     }
-                    .map_or(String::new(), |res| format!("{} ", res.descr()));
+                    .map_or_else(String::new, |res| format!("{} ", res.descr()));
                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
             };
             (
@@ -1042,10 +1042,10 @@ fn smart_resolve_context_dependent_help(
                 if let Some(span) = self.def_span(def_id) {
                     err.span_label(span, &format!("`{}` defined here", path_str));
                 }
-                let fields =
-                    self.r.field_names.get(&def_id).map_or("/* fields */".to_string(), |fields| {
-                        vec!["_"; fields.len()].join(", ")
-                    });
+                let fields = self.r.field_names.get(&def_id).map_or_else(
+                    || "/* fields */".to_string(),
+                    |fields| vec!["_"; fields.len()].join(", "),
+                );
                 err.span_suggestion(
                     span,
                     "use the tuple variant pattern syntax instead",
diff --git a/library/test/src/helpers/exit_code.rs b/library/test/src/helpers/exit_code.rs
index 31e234d981800a331a0330947d953b2d386fe3b9..50bb260762a7066649a60e1ed39c393ed2db29f8 100644
--- a/library/test/src/helpers/exit_code.rs
+++ b/library/test/src/helpers/exit_code.rs
@@ -4,7 +4,7 @@
 
 #[cfg(not(unix))]
 pub fn get_exit_code(status: ExitStatus) -> Result<i32, String> {
-    status.code().ok_or("received no exit code from child process".into())
+    status.code().ok_or_else(|| "received no exit code from child process".into())
 }
 
 #[cfg(unix)]