Make UnordItems::flat_map take UnordItems as args, too

compiler/rustc_data_structures/src/unord.rs

@@ -34,6 +34,11 @@
 pub struct UnordItems<T, I: Iterator<Item = T>>(I);
 
 impl<T, I: Iterator<Item = T>> UnordItems<T, I> {
+    #[inline]
+    pub fn new(iter: I) -> UnordItems<T, I> {
+        UnordItems(iter)
+    }
+
     #[inline]
     pub fn map<U, F: Fn(T) -> U>(self, f: F) -> UnordItems<U, impl Iterator<Item = U>> {
         UnordItems(self.0.map(f))
@@ -62,6 +67,14 @@ pub fn filter_map<U, F: Fn(T) -> Option<U>>(
         UnordItems(self.0.filter_map(f))
     }
 
+    #[inline]
+    pub fn chain(
+        self,
+        other: UnordItems<T, impl Iterator<Item = T>>,
+    ) -> UnordItems<T, impl Iterator<Item = T>> {
+        UnordItems(self.0.chain(other.0))
+    }
+
     #[inline]
     pub fn max(self) -> Option<T>
     where
@@ -102,10 +115,10 @@ pub fn count(self) -> usize {
     #[inline]
     pub fn flat_map<U, F, O>(self, f: F) -> UnordItems<O, impl Iterator<Item = O>>
     where
-        U: IntoIterator<Item = O>,
-        F: Fn(T) -> U,
+        U: Iterator<Item = O>,
+        F: Fn(T) -> UnordItems<O, U>,
     {
-        UnordItems(self.0.flat_map(f))
+        UnordItems(self.0.flat_map(move |x| f(x).0))
     }
 
     pub fn collect<C: From<UnordItems<T, I>>>(self) -> C {

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -12,6 +12,7 @@
 };
 use rustc_ast_pretty::pprust::{path_to_string, where_bound_predicate_to_string};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_data_structures::unord::UnordItems;
 use rustc_errors::codes::*;
 use rustc_errors::{
     Applicability, Diag, Diagnostic, ErrorGuaranteed, MultiSpan, SuggestionStyle, pluralize,
@@ -2670,7 +2671,11 @@ fn suggest_alternative_construction_methods(
             .extern_crate_map
             .items()
             // FIXME: This doesn't include impls like `impl Default for String`.
-            .flat_map(|(_, crate_)| self.r.tcx.implementations_of_trait((*crate_, default_trait)))
+            .flat_map(|(_, crate_)| {
+                UnordItems::new(
+                    self.r.tcx.implementations_of_trait((*crate_, default_trait)).into_iter(),
+                )
+            })
             .filter_map(|(_, simplified_self_ty)| *simplified_self_ty)
             .filter_map(|simplified_self_ty| match simplified_self_ty {
                 SimplifiedType::Adt(did) => Some(did),

src/tools/clippy/clippy_lints/src/len_without_is_empty.rs

@@ -1,6 +1,7 @@
 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::res::MaybeDef;
 use clippy_utils::{fulfill_or_allowed, get_parent_as_impl, sym};
+use rustc_data_structures::unord::UnordItems;
 use rustc_hir::def::Res;
 use rustc_hir::def_id::{DefId, DefIdSet};
 use rustc_hir::{
@@ -130,7 +131,7 @@ fn fill_trait_set(traitt: DefId, set: &mut DefIdSet, cx: &LateContext<'_>) {
         fill_trait_set(visited_trait.owner_id.to_def_id(), &mut current_and_super_traits, cx);
         let is_empty_method_found = current_and_super_traits
             .items()
-            .flat_map(|&i| cx.tcx.associated_items(i).filter_by_name_unhygienic(sym::is_empty))
+            .flat_map(|&i| UnordItems::new(cx.tcx.associated_items(i).filter_by_name_unhygienic(sym::is_empty)))
             .any(|i| i.is_method() && cx.tcx.fn_sig(i.def_id).skip_binder().inputs().skip_binder().len() == 1);
 
         if !is_empty_method_found {

src/tools/clippy/clippy_lints/src/pass_by_ref_or_value.rs

@@ -6,6 +6,7 @@
 use core::ops::ControlFlow;
 use rustc_abi::ExternAbi;
 use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::unord::UnordItems;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::attrs::InlineAttr;
@@ -181,7 +182,7 @@ fn check_poly_fn(&self, cx: &LateContext<'_>, def_id: LocalDefId, decl: &FnDecl<
                                 || typeck
                                     .adjustments()
                                     .items()
-                                    .flat_map(|(_, a)| a)
+                                    .flat_map(|(_, a)| UnordItems::new(a.iter()))
                                     .any(|a| matches!(a.kind, Adjust::Pointer(PointerCoercion::UnsafeFnPointer))))
                         {
                             continue;