use and_then/flat_map for map().flatten()

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 {

compiler/rustc_middle/src/ty/consts/valtree.rs

@@ -79,7 +79,7 @@ pub fn try_to_scalar_int(self) -> Option<ScalarInt> {
     }
 
     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

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);

compiler/rustc_session/src/options.rs

@@ -911,7 +911,7 @@ pub(crate) fn parse_instrument_xray(
         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;

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -110,8 +110,6 @@ fn implied_bounds_tys(
         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))
     }
 }