remove unused return types such as empty Results or Options that would always be Some(..)

remove unused return type of dropck::check_drop_obligations()
don't wrap return type in Option in get_macro_by_def_id() since we would always return Some(..)
remove redundant return type of back::write::optimize()
don't Option-wrap return type of compute_type_parameters() since we always return Some(..)
don't return empty Result in assemble_generator_candidates()
don't return empty Result in assemble_closure_candidates()
don't return empty result in assemble_fn_pointer_candidates()
don't return empty result in assemble_candidates_from_impls()
don't return empty result in assemble_candidates_from_auto_impls()
don't return emtpy result in assemble_candidates_for_trait_alias()
don't return empty result in assemble_builtin_bound_candidates()
don't return empty results in assemble_extension_candidates_for_traits_in_scope() and assemble_extension_candidates_for_trait()
remove redundant wrapping of return type of StripItem::strip() since it always returns Some(..)
remove unused return type of assemble_extension_candidates_for_all_traits()

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -485,7 +485,7 @@ pub(crate) unsafe fn optimize(
     diag_handler: &Handler,
     module: &ModuleCodegen<ModuleLlvm>,
     config: &ModuleConfig,
-) -> Result<(), FatalError> {
+) {
     let _timer = cgcx.prof.generic_activity_with_arg("LLVM_module_optimize", &module.name[..]);
 
     let llmod = module.module_llvm.llmod();
@@ -511,7 +511,7 @@ pub(crate) unsafe fn optimize(
                 _ => llvm::OptStage::PreLinkNoLTO,
             };
             optimize_with_new_llvm_pass_manager(cgcx, module, config, opt_level, opt_stage);
-            return Ok(());
+            return;
         }
 
         if cgcx.prof.llvm_recording_enabled() {
@@ -634,7 +634,6 @@ pub(crate) unsafe fn optimize(
         llvm::LLVMDisposePassManager(fpm);
         llvm::LLVMDisposePassManager(mpm);
     }
-    Ok(())
 }
 
 unsafe fn add_sanitizer_passes(config: &ModuleConfig, passes: &mut Vec<&'static mut llvm::Pass>) {

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -2322,13 +2322,13 @@ fn set_members_of_composite_type(
             DIB(cx),
             composite_type_metadata,
             Some(type_array),
-            type_params,
+            Some(type_params),
         );
     }
 }
 
 /// Computes the type parameters for a type, if any, for the given metadata.
-fn compute_type_parameters(cx: &CodegenCx<'ll, 'tcx>, ty: Ty<'tcx>) -> Option<&'ll DIArray> {
+fn compute_type_parameters(cx: &CodegenCx<'ll, 'tcx>, ty: Ty<'tcx>) -> &'ll DIArray {
     if let ty::Adt(def, substs) = *ty.kind() {
         if substs.types().next().is_some() {
             let generics = cx.tcx.generics_of(def.did);
@@ -2358,10 +2358,10 @@ fn compute_type_parameters(cx: &CodegenCx<'ll, 'tcx>, ty: Ty<'tcx>) -> Option<&'
                 })
                 .collect();
 
-            return Some(create_DIArray(DIB(cx), &template_params[..]));
+            return create_DIArray(DIB(cx), &template_params[..]);
         }
     }
-    return Some(create_DIArray(DIB(cx), &[]));
+    return create_DIArray(DIB(cx), &[]);
 
     fn get_parameter_names(cx: &CodegenCx<'_, '_>, generics: &ty::Generics) -> Vec<Symbol> {
         let mut names = generics

compiler/rustc_codegen_llvm/src/lib.rs

@@ -160,7 +160,7 @@ impl WriteBackendMethods for LlvmCodegenBackend {
         module: &ModuleCodegen<Self::Module>,
         config: &ModuleConfig,
     ) -> Result<(), FatalError> {
-        back::write::optimize(cgcx, diag_handler, module, config)
+        Ok(back::write::optimize(cgcx, diag_handler, module, config))
     }
     unsafe fn optimize_thin(
         cgcx: &CodegenContext<Self>,

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -185,15 +185,15 @@ impl<'a> Resolver<'a> {
 
     crate fn get_macro(&mut self, res: Res) -> Option<Lrc<SyntaxExtension>> {
         match res {
-            Res::Def(DefKind::Macro(..), def_id) => self.get_macro_by_def_id(def_id),
+            Res::Def(DefKind::Macro(..), def_id) => Some(self.get_macro_by_def_id(def_id)),
             Res::NonMacroAttr(attr_kind) => Some(self.non_macro_attr(attr_kind.is_used())),
             _ => None,
         }
     }
 
-    crate fn get_macro_by_def_id(&mut self, def_id: DefId) -> Option<Lrc<SyntaxExtension>> {
+    crate fn get_macro_by_def_id(&mut self, def_id: DefId) -> Lrc<SyntaxExtension> {
         if let Some(ext) = self.macro_map.get(&def_id) {
-            return Some(ext.clone());
+            return ext.clone();
         }
 
         let ext = Lrc::new(match self.cstore().load_macro_untracked(def_id, &self.session) {
@@ -202,7 +202,7 @@ impl<'a> Resolver<'a> {
         });
 
         self.macro_map.insert(def_id, ext.clone());
-        Some(ext)
+        ext
     }
 
     crate fn build_reduced_graph(

compiler/rustc_resolve/src/lib.rs

@@ -1991,14 +1991,13 @@ impl<'a> Resolver<'a> {
             {
                 // The macro is a proc macro derive
                 if let Some(def_id) = module.expansion.expn_data().macro_def_id {
-                    if let Some(ext) = self.get_macro_by_def_id(def_id) {
+                    let ext = self.get_macro_by_def_id(def_id);
-                        if !ext.is_builtin
+                    if !ext.is_builtin
-                            && ext.macro_kind() == MacroKind::Derive
+                        && ext.macro_kind() == MacroKind::Derive
-                            && parent.expansion.outer_expn_is_descendant_of(span.ctxt())
+                        && parent.expansion.outer_expn_is_descendant_of(span.ctxt())
-                        {
+                    {
-                            *poisoned = Some(node_id);
+                        *poisoned = Some(node_id);
-                            return module.parent;
+                        return module.parent;
-                        }
                     }
                 }
             }

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -247,7 +247,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let mut candidates = SelectionCandidateSet { vec: Vec::new(), ambiguous: false };
 
-        self.assemble_candidates_for_trait_alias(obligation, &mut candidates)?;
+        self.assemble_candidates_for_trait_alias(obligation, &mut candidates);
 
         // Other bounds. Consider both in-scope bounds from fn decl
         // and applicable impls. There is a certain set of precedence rules here.
@@ -259,11 +259,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             // User-defined copy impls are permitted, but only for
             // structs and enums.
-            self.assemble_candidates_from_impls(obligation, &mut candidates)?;
+            self.assemble_candidates_from_impls(obligation, &mut candidates);
 
             // For other types, we'll use the builtin rules.
             let copy_conditions = self.copy_clone_conditions(obligation);
-            self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates)?;
+            self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates);
         } else if lang_items.discriminant_kind_trait() == Some(def_id) {
             // `DiscriminantKind` is automatically implemented for every type.
             candidates.vec.push(DiscriminantKindCandidate);
@@ -271,7 +271,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             // Sized is never implementable by end-users, it is
             // always automatically computed.
             let sized_conditions = self.sized_conditions(obligation);
-            self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates)?;
+            self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates);
         } else if lang_items.unsize_trait() == Some(def_id) {
             self.assemble_candidates_for_unsizing(obligation, &mut candidates);
         } else {
@@ -280,13 +280,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 // for `Copy` also has builtin support for `Clone`, and tuples/arrays of `Clone`
                 // types have builtin support for `Clone`.
                 let clone_conditions = self.copy_clone_conditions(obligation);
-                self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates)?;
+                self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates);
             }
 
-            self.assemble_generator_candidates(obligation, &mut candidates)?;
+            self.assemble_generator_candidates(obligation, &mut candidates);
-            self.assemble_closure_candidates(obligation, &mut candidates)?;
+            self.assemble_closure_candidates(obligation, &mut candidates);
-            self.assemble_fn_pointer_candidates(obligation, &mut candidates)?;
+            self.assemble_fn_pointer_candidates(obligation, &mut candidates);
-            self.assemble_candidates_from_impls(obligation, &mut candidates)?;
+            self.assemble_candidates_from_impls(obligation, &mut candidates);
             self.assemble_candidates_from_object_ty(obligation, &mut candidates);
         }
 
@@ -295,7 +295,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Auto implementations have lower priority, so we only
         // consider triggering a default if there is no other impl that can apply.
         if candidates.vec.is_empty() {
-            self.assemble_candidates_from_auto_impls(obligation, &mut candidates)?;
+            self.assemble_candidates_from_auto_impls(obligation, &mut candidates);
         }
         debug!("candidate list size: {}", candidates.vec.len());
         Ok(candidates)
@@ -367,9 +367,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         if self.tcx().lang_items().gen_trait() != Some(obligation.predicate.def_id()) {
-            return Ok(());
+            return;
         }
 
         // Okay to skip binder because the substs on generator types never
@@ -388,8 +388,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
             _ => {}
         }
-
-        Ok(())
     }
 
     /// Checks for the artificial impl that the compiler will create for an obligation like `X :
@@ -402,11 +400,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         let kind = match self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) {
             Some(k) => k,
             None => {
-                return Ok(());
+                return;
             }
         };
 
@@ -435,8 +433,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
             _ => {}
         }
-
-        Ok(())
     }
 
     /// Implements one of the `Fn()` family for a fn pointer.
@@ -444,10 +440,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         // We provide impl of all fn traits for fn pointers.
         if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() {
-            return Ok(());
+            return;
         }
 
         // Okay to skip binder because what we are inspecting doesn't involve bound regions.
@@ -485,8 +481,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
             _ => {}
         }
-
-        Ok(())
     }
 
     /// Searches for impls that might apply to `obligation`.
@@ -494,7 +488,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         debug!(?obligation, "assemble_candidates_from_impls");
 
         // Essentially any user-written impl will match with an error type,
@@ -504,7 +498,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Since compilation is already guaranteed to fail, this is just
         // to try to show the 'nicest' possible errors to the user.
         if obligation.references_error() {
-            return Ok(());
+            return;
         }
 
         self.tcx().for_each_relevant_impl(
@@ -518,15 +512,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 });
             },
         );
-
-        Ok(())
     }
 
     fn assemble_candidates_from_auto_impls(
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         // Okay to skip binder here because the tests we do below do not involve bound regions.
         let self_ty = obligation.self_ty().skip_binder();
         debug!(?self_ty, "assemble_candidates_from_auto_impls");
@@ -585,8 +577,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 _ => candidates.vec.push(AutoImplCandidate(def_id)),
             }
         }
-
-        Ok(())
     }
 
     /// Searches for impls that might apply to `obligation`.
@@ -753,7 +743,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         // Okay to skip binder here because the tests we do below do not involve bound regions.
         let self_ty = obligation.self_ty().skip_binder();
         debug!(?self_ty, "assemble_candidates_for_trait_alias");
@@ -763,8 +753,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         if self.tcx().is_trait_alias(def_id) {
             candidates.vec.push(TraitAliasCandidate(def_id));
         }
-
-        Ok(())
     }
 
     /// Assembles the trait which are built-in to the language itself:
@@ -773,7 +761,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         conditions: BuiltinImplConditions<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
-    ) -> Result<(), SelectionError<'tcx>> {
+    ) {
         match conditions {
             BuiltinImplConditions::Where(nested) => {
                 debug!(?nested, "builtin_bound");
@@ -787,7 +775,5 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 candidates.ambiguous = true;
             }
         }
-
-        Ok(())
     }
 }

compiler/rustc_typeck/src/check/dropck.rs

@@ -267,15 +267,13 @@ crate fn check_drop_obligations<'a, 'tcx>(
     ty: Ty<'tcx>,
     span: Span,
     body_id: hir::HirId,
-) -> Result<(), ErrorReported> {
+) {
     debug!("check_drop_obligations typ: {:?}", ty);
 
     let cause = &ObligationCause::misc(span, body_id);
     let infer_ok = rcx.infcx.at(cause, rcx.fcx.param_env).dropck_outlives(ty);
     debug!("dropck_outlives = {:#?}", infer_ok);
     rcx.fcx.register_infer_ok_obligations(infer_ok);
-
-    Ok(())
 }
 
 // This is an implementation of the TypeRelation trait with the

compiler/rustc_typeck/src/check/method/probe.rs

@@ -423,9 +423,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             probe_cx.assemble_inherent_candidates();
             match scope {
                 ProbeScope::TraitsInScope => {
-                    probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)?
+                    probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id)
                 }
-                ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits()?,
+                ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(),
             };
             op(probe_cx)
         })
@@ -866,35 +866,29 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
-    fn assemble_extension_candidates_for_traits_in_scope(
+    fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) {
-        &mut self,
-        expr_hir_id: hir::HirId,
-    ) -> Result<(), MethodError<'tcx>> {
         let mut duplicates = FxHashSet::default();
         let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id);
         if let Some(applicable_traits) = opt_applicable_traits {
             for trait_candidate in applicable_traits.iter() {
                 let trait_did = trait_candidate.def_id;
                 if duplicates.insert(trait_did) {
-                    let result = self.assemble_extension_candidates_for_trait(
+                    self.assemble_extension_candidates_for_trait(
                         &trait_candidate.import_ids,
                         trait_did,
                     );
-                    result?;
                 }
             }
         }
-        Ok(())
     }
 
-    fn assemble_extension_candidates_for_all_traits(&mut self) -> Result<(), MethodError<'tcx>> {
+    fn assemble_extension_candidates_for_all_traits(&mut self) {
         let mut duplicates = FxHashSet::default();
         for trait_info in suggest::all_traits(self.tcx) {
             if duplicates.insert(trait_info.def_id) {
-                self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id)?;
+                self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id);
             }
         }
-        Ok(())
     }
 
     pub fn matches_return_type(
@@ -932,7 +926,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         &mut self,
         import_ids: &SmallVec<[LocalDefId; 1]>,
         trait_def_id: DefId,
-    ) -> Result<(), MethodError<'tcx>> {
+    ) {
         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
         let trait_substs = self.fresh_item_substs(trait_def_id);
         let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
@@ -980,7 +974,6 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 );
             }
         }
-        Ok(())
     }
 
     fn candidate_method_names(&self) -> Vec<Ident> {
@@ -1027,7 +1020,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         let span = self.span;
         let tcx = self.tcx;
 
-        self.assemble_extension_candidates_for_all_traits()?;
+        self.assemble_extension_candidates_for_all_traits();
 
         let out_of_scope_traits = match self.pick_core() {
             Some(Ok(p)) => vec![p.item.container.id()],

compiler/rustc_typeck/src/check/regionck.rs

@@ -325,7 +325,7 @@ impl<'a, 'tcx> RegionCtxt<'a, 'tcx> {
         pat.each_binding(|_, hir_id, span, _| {
             let typ = self.resolve_node_type(hir_id);
             let body_id = self.body_id;
-            let _ = dropck::check_drop_obligations(self, typ, span, body_id);
+            dropck::check_drop_obligations(self, typ, span, body_id);
         })
     }
 }
@@ -488,7 +488,7 @@ impl<'a, 'tcx> RegionCtxt<'a, 'tcx> {
             if place_with_id.place.projections.is_empty() {
                 let typ = self.resolve_type(place_with_id.place.ty());
                 let body_id = self.body_id;
-                let _ = dropck::check_drop_obligations(self, typ, span, body_id);
+                dropck::check_drop_obligations(self, typ, span, body_id);
             }
         }
     }

src/librustdoc/fold.rs

@@ -3,12 +3,12 @@ use crate::clean::*;
 crate struct StripItem(pub Item);
 
 impl StripItem {
-    crate fn strip(self) -> Option<Item> {
+    crate fn strip(self) -> Item {
         match self.0 {
-            Item { kind: box StrippedItem(..), .. } => Some(self.0),
+            Item { kind: box StrippedItem(..), .. } => self.0,
             mut i => {
                 i.kind = box StrippedItem(i.kind);
-                Some(i)
+                i
             }
         }
     }

src/librustdoc/passes/strip_hidden.rs

@@ -49,7 +49,7 @@ impl<'a> DocFolder for Stripper<'a> {
                     let old = mem::replace(&mut self.update_retained, false);
                     let ret = StripItem(self.fold_item_recur(i)).strip();
                     self.update_retained = old;
-                    return ret;
+                    return Some(ret);
                 }
                 _ => return None,
             }

src/librustdoc/passes/stripper.rs

@@ -51,7 +51,7 @@ impl<'a> DocFolder for Stripper<'a> {
 
             clean::StructFieldItem(..) => {
                 if !i.visibility.is_public() {
-                    return StripItem(i).strip();
+                    return Some(StripItem(i).strip());
                 }
             }
 
@@ -61,7 +61,7 @@ impl<'a> DocFolder for Stripper<'a> {
                     let old = mem::replace(&mut self.update_retained, false);
                     let ret = StripItem(self.fold_item_recur(i)).strip();
                     self.update_retained = old;
-                    return ret;
+                    return Some(ret);
                 }
             }