diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index efa0c13226ecf..4f8b5abd9010c 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -378,8 +378,7 @@ pub(crate) fn get_dllimport<'tcx>(
     name: &str,
 ) -> Option<&'tcx DllImport> {
     tcx.native_library(id)
-        .map(|lib| lib.dll_imports.iter().find(|di| di.name.as_str() == name))
-        .flatten()
+        .and_then(|lib| lib.dll_imports.iter().find(|di| di.name.as_str() == name))
 }
 
 pub(crate) fn is_mingw_gnu_toolchain(target: &Target) -> bool {
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index cd5c92f7342de..558253f727bcc 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -677,8 +677,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     );
                 }
                 if let Rvalue::CopyForDeref(place) = rvalue {
-                    if !place.ty(&self.body.local_decls, self.tcx).ty.builtin_deref(true).is_some()
-                    {
+                    if place.ty(&self.body.local_decls, self.tcx).ty.builtin_deref(true).is_none() {
                         self.fail(
                             location,
                             "`CopyForDeref` should only be used for dereferenceable types",
diff --git a/compiler/rustc_hir_analysis/src/astconv/errors.rs b/compiler/rustc_hir_analysis/src/astconv/errors.rs
index 672e7176fde09..113c3f08ab9ae 100644
--- a/compiler/rustc_hir_analysis/src/astconv/errors.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/errors.rs
@@ -483,8 +483,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 [segment] if segment.args.is_none() => {
                     trait_bound_spans = vec![segment.ident.span];
                     associated_types = associated_types
-                        .into_iter()
-                        .map(|(_, items)| (segment.ident.span, items))
+                        .into_values()
+                        .map(|items| (segment.ident.span, items))
                         .collect();
                 }
                 _ => {}
diff --git a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
index 58902cd292c11..ee1c6fbfd650f 100644
--- a/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
+++ b/compiler/rustc_hir_typeck/src/expr_use_visitor.rs
@@ -559,7 +559,7 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
                 // struct; however, when EUV is run during typeck, it
                 // may not. This will generate an error earlier in typeck,
                 // so we can just ignore it.
-                if !self.tcx().sess.has_errors().is_some() {
+                if self.tcx().sess.has_errors().is_none() {
                     span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
                 }
             }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 75c3d9f641dda..1f9c993adff22 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -978,7 +978,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             let (_, sig, reg) = ty::print::FmtPrinter::new(self.tcx, Namespace::TypeNS)
                 .name_all_regions(sig)
                 .unwrap();
-            let lts: Vec<String> = reg.into_iter().map(|(_, kind)| kind.to_string()).collect();
+            let lts: Vec<String> = reg.into_values().map(|kind| kind.to_string()).collect();
             (if lts.is_empty() { String::new() } else { format!("for<{}> ", lts.join(", ")) }, sig)
         };
 
diff --git a/compiler/rustc_middle/src/middle/mod.rs b/compiler/rustc_middle/src/middle/mod.rs
index 0b6774f1b1fe1..9c25f3009ba81 100644
--- a/compiler/rustc_middle/src/middle/mod.rs
+++ b/compiler/rustc_middle/src/middle/mod.rs
@@ -19,7 +19,7 @@ pub mod lib_features {
                 .stable
                 .iter()
                 .map(|(f, (s, _))| (*f, Some(*s)))
-                .chain(self.unstable.iter().map(|(f, _)| (*f, None)))
+                .chain(self.unstable.keys().map(|f| (*f, None)))
                 .collect();
             all_features.sort_unstable_by(|a, b| a.0.as_str().partial_cmp(b.0.as_str()).unwrap());
             all_features
diff --git a/compiler/rustc_middle/src/ty/consts/valtree.rs b/compiler/rustc_middle/src/ty/consts/valtree.rs
index 5ed4af2e9229d..8b96864ddd7c9 100644
--- a/compiler/rustc_middle/src/ty/consts/valtree.rs
+++ b/compiler/rustc_middle/src/ty/consts/valtree.rs
@@ -79,7 +79,7 @@ impl<'tcx> ValTree<'tcx> {
     }
 
     pub fn try_to_target_usize(self, tcx: TyCtxt<'tcx>) -> Option<u64> {
-        self.try_to_scalar_int().map(|s| s.try_to_target_usize(tcx).ok()).flatten()
+        self.try_to_scalar_int().and_then(|s| s.try_to_target_usize(tcx).ok())
     }
 
     /// Get the values inside the ValTree as a slice of bytes. This only works for
diff --git a/compiler/rustc_mir_build/src/build/expr/as_constant.rs b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
index cfacb5ea32777..99291740ac82f 100644
--- a/compiler/rustc_mir_build/src/build/expr/as_constant.rs
+++ b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
@@ -62,21 +62,21 @@ pub fn as_constant_inner<'tcx>(
             Constant { span, user_ty: None, literal }
         }
         ExprKind::NonHirLiteral { lit, ref user_ty } => {
-            let user_ty = user_ty.as_ref().map(push_cuta).flatten();
+            let user_ty = user_ty.as_ref().and_then(push_cuta);
 
             let literal = ConstantKind::Val(ConstValue::Scalar(Scalar::Int(lit)), ty);
 
             Constant { span, user_ty, literal }
         }
         ExprKind::ZstLiteral { ref user_ty } => {
-            let user_ty = user_ty.as_ref().map(push_cuta).flatten();
+            let user_ty = user_ty.as_ref().and_then(push_cuta);
 
             let literal = ConstantKind::Val(ConstValue::ZeroSized, ty);
 
             Constant { span, user_ty, literal }
         }
         ExprKind::NamedConst { def_id, substs, ref user_ty } => {
-            let user_ty = user_ty.as_ref().map(push_cuta).flatten();
+            let user_ty = user_ty.as_ref().and_then(push_cuta);
 
             let uneval = mir::UnevaluatedConst::new(ty::WithOptConstParam::unknown(def_id), substs);
             let literal = ConstantKind::Unevaluated(uneval, ty);
diff --git a/compiler/rustc_monomorphize/src/partitioning/default.rs b/compiler/rustc_monomorphize/src/partitioning/default.rs
index 50bcc3336d60d..482b78d42e377 100644
--- a/compiler/rustc_monomorphize/src/partitioning/default.rs
+++ b/compiler/rustc_monomorphize/src/partitioning/default.rs
@@ -89,10 +89,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
         }
 
         PreInliningPartitioning {
-            codegen_units: codegen_units
-                .into_iter()
-                .map(|(_, codegen_unit)| codegen_unit)
-                .collect(),
+            codegen_units: codegen_units.into_values().map(|codegen_unit| codegen_unit).collect(),
             roots,
             internalization_candidates,
         }
diff --git a/compiler/rustc_passes/src/entry.rs b/compiler/rustc_passes/src/entry.rs
index f3e683f4b3a0a..8c3dff23b272d 100644
--- a/compiler/rustc_passes/src/entry.rs
+++ b/compiler/rustc_passes/src/entry.rs
@@ -206,7 +206,7 @@ fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_>) {
     // The file may be empty, which leads to the diagnostic machinery not emitting this
     // note. This is a relatively simple way to detect that case and emit a span-less
     // note instead.
-    let file_empty = !tcx.sess.source_map().lookup_line(sp.hi()).is_ok();
+    let file_empty = tcx.sess.source_map().lookup_line(sp.hi()).is_err();
 
     tcx.sess.emit_err(NoMainErr {
         sp,
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 44a3d4e628ebc..e69a9d0aecaf4 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1669,8 +1669,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
     ) -> Option<Symbol> {
         let mut candidates = self
             .extern_prelude
-            .iter()
-            .map(|(ident, _)| ident.name)
+            .keys()
+            .map(|ident| ident.name)
             .chain(
                 self.module_map
                     .iter()
@@ -2007,7 +2007,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // 1) some consistent ordering for emitted diagnostics, and
         // 2) `std` suggestions before `core` suggestions.
         let mut extern_crate_names =
-            self.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
+            self.extern_prelude.keys().map(|ident| ident.name).collect::<Vec<_>>();
         extern_crate_names.sort_by(|a, b| b.as_str().partial_cmp(a.as_str()).unwrap());
 
         for name in extern_crate_names.into_iter() {
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 52f0b65fad672..06206efb9abd5 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -389,7 +389,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
         }
 
-        assert!(force || !finalize.is_some()); // `finalize` implies `force`
+        assert!(force || finalize.is_none()); // `finalize` implies `force`
 
         // Make sure `self`, `super` etc produce an error when passed to here.
         if orig_ident.is_path_segment_keyword() {
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index f66bad1d429a9..b82b07bcf0cc8 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -2421,8 +2421,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     .iter()
                     .rfind(|r| matches!(r.kind, ItemRibKind(_)))
                     .expect("associated item outside of an item");
-                seen_bindings
-                    .extend(parent_rib.bindings.iter().map(|(ident, _)| (*ident, ident.span)));
+                seen_bindings.extend(parent_rib.bindings.keys().map(|ident| (*ident, ident.span)));
             };
             add_bindings_for_ns(ValueNS);
             add_bindings_for_ns(TypeNS);
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index c75af48e80af4..be5d4fca7a009 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -911,7 +911,7 @@ mod parse {
         let mut seen_instruction_threshold = false;
         let mut seen_skip_entry = false;
         let mut seen_skip_exit = false;
-        for option in v.into_iter().map(|v| v.split(',')).flatten() {
+        for option in v.into_iter().flat_map(|v| v.split(',')) {
             match option {
                 "always" if !seen_always && !seen_never => {
                     options.always = true;
diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index 6d2dc94845d0d..cff3d277a78fb 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -110,8 +110,6 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
         body_id: LocalDefId,
         tys: FxIndexSet<Ty<'tcx>>,
     ) -> Bounds<'a, 'tcx> {
-        tys.into_iter()
-            .map(move |ty| self.implied_outlives_bounds(param_env, body_id, ty))
-            .flatten()
+        tys.into_iter().flat_map(move |ty| self.implied_outlives_bounds(param_env, body_id, ty))
     }
 }
diff --git a/compiler/rustc_traits/src/chalk/lowering.rs b/compiler/rustc_traits/src/chalk/lowering.rs
index 0e9bccba8d4c5..527f6013a1516 100644
--- a/compiler/rustc_traits/src/chalk/lowering.rs
+++ b/compiler/rustc_traits/src/chalk/lowering.rs
@@ -909,8 +909,7 @@ pub(crate) fn collect_bound_vars<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
             .or_else(|| bug!("Skipped bound var index: parameters={:?}", parameters));
     });
 
-    let binders =
-        chalk_ir::VariableKinds::from_iter(interner, parameters.into_iter().map(|(_, v)| v));
+    let binders = chalk_ir::VariableKinds::from_iter(interner, parameters.into_values());
 
     (new_ty, binders, named_parameters)
 }