Rollup merge of #105541 - compiler-errors:iter-comb, r=cjgillot

Simplify some iterator combinators

Saw a `flat_map().next()` instead of a `find_map()` in some method probe code, so did a quick search for some similar usages.

12 files changed, 98 insertions, 207 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 3c3cb8c6b9c..50cd13a2ccc 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -527,26 +527,21 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             // that are *partially* initialized by assigning to a field of an uninitialized
             // binding. We differentiate between them for more accurate wording here.
             "isn't fully initialized"
-        } else if spans
-            .iter()
-            .filter(|i| {
-                // We filter these to avoid misleading wording in cases like the following,
-                // where `x` has an `init`, but it is in the same place we're looking at:
-                // ```
-                // let x;
-                // x += 1;
-                // ```
-                !i.contains(span)
-                    // We filter these to avoid incorrect main message on `match-cfg-fake-edges.rs`
-                        && !visitor
-                            .errors
-                            .iter()
-                            .map(|(sp, _)| *sp)
-                            .any(|sp| span < sp && !sp.contains(span))
-            })
-            .count()
-            == 0
-        {
+        } else if !spans.iter().any(|i| {
+            // We filter these to avoid misleading wording in cases like the following,
+            // where `x` has an `init`, but it is in the same place we're looking at:
+            // ```
+            // let x;
+            // x += 1;
+            // ```
+            !i.contains(span)
+            // We filter these to avoid incorrect main message on `match-cfg-fake-edges.rs`
+            && !visitor
+                .errors
+                .iter()
+                .map(|(sp, _)| *sp)
+                .any(|sp| span < sp && !sp.contains(span))
+        }) {
             show_assign_sugg = true;
             "isn't initialized"
         } else {
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index bcc8afbfd95..567a9814fcc 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -4,9 +4,9 @@
 
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
+use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
-use rustc_hir::{self as hir, Item, ItemKind, Node};
 use rustc_infer::infer::{
     error_reporting::nice_region_error::{
         self, find_anon_type, find_param_with_region, suggest_adding_lifetime_params,
@@ -291,71 +291,6 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         outlives_suggestion.add_suggestion(self);
     }
 
-    fn get_impl_ident_and_self_ty_from_trait(
-        &self,
-        def_id: DefId,
-        trait_objects: &FxIndexSet<DefId>,
-    ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
-        let tcx = self.infcx.tcx;
-        match tcx.hir().get_if_local(def_id) {
-            Some(Node::ImplItem(impl_item)) => {
-                match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id()).def_id)
-                {
-                    Some(Node::Item(Item {
-                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                        ..
-                    })) => Some((impl_item.ident, self_ty)),
-                    _ => None,
-                }
-            }
-            Some(Node::TraitItem(trait_item)) => {
-                let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
-                match tcx.hir().find_by_def_id(trait_did.def_id) {
-                    Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
-                        // The method being called is defined in the `trait`, but the `'static`
-                        // obligation comes from the `impl`. Find that `impl` so that we can point
-                        // at it in the suggestion.
-                        let trait_did = trait_did.to_def_id();
-                        match tcx
-                            .hir()
-                            .trait_impls(trait_did)
-                            .iter()
-                            .filter_map(|&impl_did| {
-                                match tcx.hir().get_if_local(impl_did.to_def_id()) {
-                                    Some(Node::Item(Item {
-                                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                                        ..
-                                    })) if trait_objects.iter().all(|did| {
-                                        // FIXME: we should check `self_ty` against the receiver
-                                        // type in the `UnifyReceiver` context, but for now, use
-                                        // this imperfect proxy. This will fail if there are
-                                        // multiple `impl`s for the same trait like
-                                        // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
-                                        // In that case, only the first one will get suggestions.
-                                        let mut traits = vec![];
-                                        let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
-                                        hir_v.visit_ty(self_ty);
-                                        !traits.is_empty()
-                                    }) =>
-                                    {
-                                        Some(self_ty)
-                                    }
-                                    _ => None,
-                                }
-                            })
-                            .next()
-                        {
-                            Some(self_ty) => Some((trait_item.ident, self_ty)),
-                            _ => None,
-                        }
-                    }
-                    _ => None,
-                }
-            }
-            _ => None,
-        }
-    }
-
     /// Report an error because the universal region `fr` was required to outlive
     /// `outlived_fr` but it is not known to do so. For example:
     ///
@@ -850,7 +785,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         visitor.visit_ty(param.param_ty);
 
         let Some((ident, self_ty)) =
-            self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &visitor.0) else {return};
+            NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, instance.def_id(), &visitor.0) else { return; };
 
         self.suggest_constrain_dyn_trait_in_impl(diag, &visitor.0, ident, self_ty);
     }
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index effb2de4827..a92242b2615 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -1244,7 +1244,7 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
     ) -> RValue<'gcc> {
         // FIXME(antoyo): remove when having a proper API.
         let gcc_func = unsafe { std::mem::transmute(func) };
-        let call = if self.functions.borrow().values().find(|value| **value == gcc_func).is_some() {
+        let call = if self.functions.borrow().values().any(|value| *value == gcc_func) {
             self.function_call(func, args, funclet)
         }
         else {
diff --git a/compiler/rustc_codegen_gcc/src/context.rs b/compiler/rustc_codegen_gcc/src/context.rs
index 837708aeb0e..4424b31c054 100644
--- a/compiler/rustc_codegen_gcc/src/context.rs
+++ b/compiler/rustc_codegen_gcc/src/context.rs
@@ -253,7 +253,7 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
 
     pub fn rvalue_as_function(&self, value: RValue<'gcc>) -> Function<'gcc> {
         let function: Function<'gcc> = unsafe { std::mem::transmute(value) };
-        debug_assert!(self.functions.borrow().values().find(|value| **value == function).is_some(),
+        debug_assert!(self.functions.borrow().values().any(|value| *value == function),
             "{:?} ({:?}) is not a function", value, value.get_type());
         function
     }
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index b06927f9662..cecf3d3f1e0 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -240,10 +240,8 @@ fn typeck_with_fallback<'tcx>(
                         }),
                         Node::Expr(&hir::Expr { kind: hir::ExprKind::InlineAsm(asm), .. })
                         | Node::Item(&hir::Item { kind: hir::ItemKind::GlobalAsm(asm), .. }) => {
-                            let operand_ty = asm
-                                .operands
-                                .iter()
-                                .filter_map(|(op, _op_sp)| match op {
+                            let operand_ty =
+                                asm.operands.iter().find_map(|(op, _op_sp)| match op {
                                     hir::InlineAsmOperand::Const { anon_const }
                                         if anon_const.hir_id == id =>
                                     {
@@ -259,8 +257,7 @@ fn typeck_with_fallback<'tcx>(
                                         }))
                                     }
                                     _ => None,
-                                })
-                                .next();
+                                });
                             operand_ty.unwrap_or_else(fallback)
                         }
                         _ => fallback(),
diff --git a/compiler/rustc_hir_typeck/src/method/prelude2021.rs b/compiler/rustc_hir_typeck/src/method/prelude2021.rs
index dea14dd93d6..3d6c2119bea 100644
--- a/compiler/rustc_hir_typeck/src/method/prelude2021.rs
+++ b/compiler/rustc_hir_typeck/src/method/prelude2021.rs
@@ -341,8 +341,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Find an identifier with which this trait was imported (note that `_` doesn't count).
         let any_id = import_items
             .iter()
-            .filter_map(|item| if item.ident.name != Underscore { Some(item.ident) } else { None })
-            .next();
+            .find_map(|item| if item.ident.name != Underscore { Some(item.ident) } else { None });
         if let Some(any_id) = any_id {
             if any_id.name == Empty {
                 // Glob import, so just use its name.
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 1afaae0e020..2daf1979ee5 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -1111,7 +1111,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 // a raw pointer
                 !step.self_ty.references_error() && !step.from_unsafe_deref
             })
-            .flat_map(|step| {
+            .find_map(|step| {
                 let InferOk { value: self_ty, obligations: _ } = self
                     .fcx
                     .probe_instantiate_query_response(
@@ -1147,7 +1147,6 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         })
                     })
             })
-            .next()
     }
 
     /// For each type `T` in the step list, this attempts to find a method where
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 71c3803e64f..b04ef55a994 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -257,9 +257,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self.tcx
                             .inherent_impls(adt_def.did())
                             .iter()
-                            .filter_map(|def_id| self.associated_value(*def_id, item_name))
-                            .count()
-                            >= 1
+                            .any(|def_id| self.associated_value(*def_id, item_name).is_some())
                     } else {
                         false
                     }
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
index 9bd2202d260..d9cdfa9dd4f 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -239,7 +239,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             let mut v = TraitObjectVisitor(FxIndexSet::default());
             v.visit_ty(param.param_ty);
             if let Some((ident, self_ty)) =
-                self.get_impl_ident_and_self_ty_from_trait(item_def_id, &v.0)
+                NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, item_def_id, &v.0)
                 && self.suggest_constrain_dyn_trait_in_impl(&mut err, &v.0, ident, self_ty)
             {
                 override_error_code = Some(ident.name);
@@ -309,19 +309,12 @@ pub fn suggest_new_region_bound(
                 let did = item_id.owner_id.to_def_id();
                 let ty = tcx.mk_opaque(did, ty::InternalSubsts::identity_for_item(tcx, did));
 
-                if let Some(span) = opaque
-                    .bounds
-                    .iter()
-                    .filter_map(|arg| match arg {
-                        GenericBound::Outlives(Lifetime {
-                            res: LifetimeName::Static,
-                            ident,
-                            ..
-                        }) => Some(ident.span),
-                        _ => None,
-                    })
-                    .next()
-                {
+                if let Some(span) = opaque.bounds.iter().find_map(|arg| match arg {
+                    GenericBound::Outlives(Lifetime {
+                        res: LifetimeName::Static, ident, ..
+                    }) => Some(ident.span),
+                    _ => None,
+                }) {
                     if let Some(explicit_static) = &explicit_static {
                         err.span_suggestion_verbose(
                             span,
@@ -338,20 +331,14 @@ pub fn suggest_new_region_bound(
                             Applicability::MaybeIncorrect,
                         );
                     }
-                } else if opaque
-                    .bounds
-                    .iter()
-                    .filter_map(|arg| match arg {
-                        GenericBound::Outlives(Lifetime { ident, .. })
-                            if ident.name.to_string() == lifetime_name =>
-                        {
-                            Some(ident.span)
-                        }
-                        _ => None,
-                    })
-                    .next()
-                    .is_some()
-                {
+                } else if opaque.bounds.iter().any(|arg| match arg {
+                    GenericBound::Outlives(Lifetime { ident, .. })
+                        if ident.name.to_string() == lifetime_name =>
+                    {
+                        true
+                    }
+                    _ => false,
+                }) {
                 } else {
                     err.span_suggestion_verbose(
                         fn_return.span.shrink_to_hi(),
@@ -403,66 +390,54 @@ pub fn suggest_new_region_bound(
 }
 
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
-    fn get_impl_ident_and_self_ty_from_trait(
-        &self,
+    pub fn get_impl_ident_and_self_ty_from_trait(
+        tcx: TyCtxt<'tcx>,
         def_id: DefId,
         trait_objects: &FxIndexSet<DefId>,
     ) -> Option<(Ident, &'tcx hir::Ty<'tcx>)> {
-        let tcx = self.tcx();
-        match tcx.hir().get_if_local(def_id) {
-            Some(Node::ImplItem(impl_item)) => {
-                match tcx.hir().find_by_def_id(tcx.hir().get_parent_item(impl_item.hir_id()).def_id)
+        match tcx.hir().get_if_local(def_id)? {
+            Node::ImplItem(impl_item) => {
+                let impl_did = tcx.hir().get_parent_item(impl_item.hir_id());
+                if let hir::OwnerNode::Item(Item {
+                    kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
+                    ..
+                }) = tcx.hir().owner(impl_did)
                 {
-                    Some(Node::Item(Item {
-                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                        ..
-                    })) => Some((impl_item.ident, self_ty)),
-                    _ => None,
+                    Some((impl_item.ident, self_ty))
+                } else {
+                    None
                 }
             }
-            Some(Node::TraitItem(trait_item)) => {
-                let trait_did = tcx.hir().get_parent_item(trait_item.hir_id());
-                match tcx.hir().find_by_def_id(trait_did.def_id) {
-                    Some(Node::Item(Item { kind: ItemKind::Trait(..), .. })) => {
-                        // The method being called is defined in the `trait`, but the `'static`
-                        // obligation comes from the `impl`. Find that `impl` so that we can point
-                        // at it in the suggestion.
-                        let trait_did = trait_did.to_def_id();
-                        match tcx
-                            .hir()
-                            .trait_impls(trait_did)
-                            .iter()
-                            .filter_map(|&impl_did| {
-                                match tcx.hir().get_if_local(impl_did.to_def_id()) {
-                                    Some(Node::Item(Item {
-                                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
-                                        ..
-                                    })) if trait_objects.iter().all(|did| {
-                                        // FIXME: we should check `self_ty` against the receiver
-                                        // type in the `UnifyReceiver` context, but for now, use
-                                        // this imperfect proxy. This will fail if there are
-                                        // multiple `impl`s for the same trait like
-                                        // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
-                                        // In that case, only the first one will get suggestions.
-                                        let mut traits = vec![];
-                                        let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
-                                        hir_v.visit_ty(self_ty);
-                                        !traits.is_empty()
-                                    }) =>
-                                    {
-                                        Some(self_ty)
-                                    }
-                                    _ => None,
-                                }
-                            })
-                            .next()
-                        {
-                            Some(self_ty) => Some((trait_item.ident, self_ty)),
-                            _ => None,
-                        }
+            Node::TraitItem(trait_item) => {
+                let trait_id = tcx.hir().get_parent_item(trait_item.hir_id());
+                debug_assert_eq!(tcx.def_kind(trait_id.def_id), hir::def::DefKind::Trait);
+                // The method being called is defined in the `trait`, but the `'static`
+                // obligation comes from the `impl`. Find that `impl` so that we can point
+                // at it in the suggestion.
+                let trait_did = trait_id.to_def_id();
+                tcx.hir().trait_impls(trait_did).iter().find_map(|&impl_did| {
+                    if let Node::Item(Item {
+                        kind: ItemKind::Impl(hir::Impl { self_ty, .. }),
+                        ..
+                    }) = tcx.hir().find_by_def_id(impl_did)?
+                        && trait_objects.iter().all(|did| {
+                            // FIXME: we should check `self_ty` against the receiver
+                            // type in the `UnifyReceiver` context, but for now, use
+                            // this imperfect proxy. This will fail if there are
+                            // multiple `impl`s for the same trait like
+                            // `impl Foo for Box<dyn Bar>` and `impl Foo for dyn Bar`.
+                            // In that case, only the first one will get suggestions.
+                            let mut traits = vec![];
+                            let mut hir_v = HirTraitObjectVisitor(&mut traits, *did);
+                            hir_v.visit_ty(self_ty);
+                            !traits.is_empty()
+                        })
+                    {
+                        Some((trait_item.ident, *self_ty))
+                    } else {
+                        None
                     }
-                    _ => None,
-                }
+                })
             }
             _ => None,
         }
@@ -493,7 +468,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 
         // Get the `Ident` of the method being called and the corresponding `impl` (to point at
         // `Bar` in `impl Foo for dyn Bar {}` and the definition of the method being called).
-        let Some((ident, self_ty)) = self.get_impl_ident_and_self_ty_from_trait(instance.def_id(), &v.0) else {
+        let Some((ident, self_ty)) = NiceRegionError::get_impl_ident_and_self_ty_from_trait(tcx, instance.def_id(), &v.0) else {
             return false;
         };
 
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index a7a5234049f..525079681ca 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -256,7 +256,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                         cx.tcx,
                         cx.tcx.explicit_item_bounds(def).iter().cloned(),
                     )
-                    .filter_map(|obligation| {
+                    .find_map(|obligation| {
                         // We only look at the `DefId`, so it is safe to skip the binder here.
                         if let ty::PredicateKind::Clause(ty::Clause::Trait(
                             ref poly_trait_predicate,
@@ -270,22 +270,17 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                         }
                     })
                     .map(|inner| MustUsePath::Opaque(Box::new(inner)))
-                    .next()
                 }
-                ty::Dynamic(binders, _, _) => binders
-                    .iter()
-                    .filter_map(|predicate| {
-                        if let ty::ExistentialPredicate::Trait(ref trait_ref) =
-                            predicate.skip_binder()
-                        {
-                            let def_id = trait_ref.def_id;
-                            is_def_must_use(cx, def_id, span)
-                        } else {
-                            None
-                        }
-                        .map(|inner| MustUsePath::TraitObject(Box::new(inner)))
-                    })
-                    .next(),
+                ty::Dynamic(binders, _, _) => binders.iter().find_map(|predicate| {
+                    if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder()
+                    {
+                        let def_id = trait_ref.def_id;
+                        is_def_must_use(cx, def_id, span)
+                            .map(|inner| MustUsePath::TraitObject(Box::new(inner)))
+                    } else {
+                        None
+                    }
+                }),
                 ty::Tuple(tys) => {
                     let elem_exprs = if let hir::ExprKind::Tup(elem_exprs) = expr.kind {
                         debug_assert_eq!(elem_exprs.len(), tys.len());
diff --git a/compiler/rustc_macros/src/symbols/tests.rs b/compiler/rustc_macros/src/symbols/tests.rs
index 842d2a97718..bd0c08a53c4 100644
--- a/compiler/rustc_macros/src/symbols/tests.rs
+++ b/compiler/rustc_macros/src/symbols/tests.rs
@@ -16,14 +16,13 @@ fn test_symbols() {
     let m: &syn::ItemMacro = file
         .items
         .iter()
-        .filter_map(|i| {
+        .find_map(|i| {
             if let syn::Item::Macro(m) = i {
                 if m.mac.path == symbols_path { Some(m) } else { None }
             } else {
                 None
             }
         })
-        .next()
         .expect("did not find `symbols!` macro invocation.");
 
     let body_tokens = m.mac.tokens.clone();
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 0c4b35b8833..e41fe325b81 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -820,13 +820,12 @@ impl<'a> Resolver<'a> {
             // binding if it exists. What we really want here is having two separate scopes in
             // a module - one for non-globs and one for globs, but until that's done use this
             // hack to avoid inconsistent resolution ICEs during import validation.
-            let binding = [resolution.binding, resolution.shadowed_glob]
-                .into_iter()
-                .filter_map(|binding| match (binding, ignore_binding) {
+            let binding = [resolution.binding, resolution.shadowed_glob].into_iter().find_map(
+                |binding| match (binding, ignore_binding) {
                     (Some(binding), Some(ignored)) if ptr::eq(binding, ignored) => None,
                     _ => binding,
-                })
-                .next();
+                },
+            );
             let Some(binding) = binding else {
                 return Err((Determined, Weak::No));
             };