fix more clippy::complexity findings

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -597,10 +597,7 @@ impl<'a> TraitDef<'a> {
 
             let mut ty_params = params
                 .iter()
-                .filter_map(|param| match param.kind {
-                    ast::GenericParamKind::Type { .. } => Some(param),
-                    _ => None,
-                })
+                .filter(|param| matches!(param.kind,  ast::GenericParamKind::Type{..}))
                 .peekable();
 
             if ty_params.peek().is_some() {

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -854,8 +854,8 @@ fn generic_simd_intrinsic(
         ));
     }
 
-    if name_str.starts_with("simd_shuffle") {
-        let n: u64 = name_str["simd_shuffle".len()..].parse().unwrap_or_else(|_| {
+    if let Some(stripped) = name_str.strip_prefix("simd_shuffle") {
+        let n: u64 = stripped.parse().unwrap_or_else(|_| {
             span_bug!(span, "bad `simd_shuffle` instruction only caught in codegen?")
         });
 

compiler/rustc_llvm/build.rs

@@ -201,10 +201,10 @@ fn main() {
     cmd.args(&components);
 
     for lib in output(&mut cmd).split_whitespace() {
-        let name = if lib.starts_with("-l") {
-            &lib[2..]
-        } else if lib.starts_with('-') {
-            &lib[1..]
+        let name = if let Some(stripped) = lib.strip_prefix("-l") {
+            stripped
+        } else if let Some(stripped) = lib.strip_prefix('-') {
+            stripped
         } else if Path::new(lib).exists() {
             // On MSVC llvm-config will print the full name to libraries, but
             // we're only interested in the name part
@@ -241,17 +241,17 @@ fn main() {
     cmd.arg(llvm_link_arg).arg("--ldflags");
     for lib in output(&mut cmd).split_whitespace() {
         if is_crossed {
-            if lib.starts_with("-LIBPATH:") {
-                println!("cargo:rustc-link-search=native={}", lib[9..].replace(&host, &target));
-            } else if lib.starts_with("-L") {
-                println!("cargo:rustc-link-search=native={}", lib[2..].replace(&host, &target));
+            if let Some(stripped) = lib.strip_prefix("-LIBPATH:") {
+                println!("cargo:rustc-link-search=native={}", stripped.replace(&host, &target));
+            } else if let Some(stripped) = lib.strip_prefix("-L") {
+                println!("cargo:rustc-link-search=native={}", stripped.replace(&host, &target));
             }
-        } else if lib.starts_with("-LIBPATH:") {
-            println!("cargo:rustc-link-search=native={}", &lib[9..]);
-        } else if lib.starts_with("-l") {
-            println!("cargo:rustc-link-lib={}", &lib[2..]);
-        } else if lib.starts_with("-L") {
-            println!("cargo:rustc-link-search=native={}", &lib[2..]);
+        } else if let Some(stripped) = lib.strip_prefix("-LIBPATH:") {
+            println!("cargo:rustc-link-search=native={}", stripped);
+        } else if let Some(stripped) = lib.strip_prefix("-l") {
+            println!("cargo:rustc-link-lib={}", stripped);
+        } else if let Some(stripped) = lib.strip_prefix("-L") {
+            println!("cargo:rustc-link-search=native={}", stripped);
         }
     }
 
@@ -262,10 +262,10 @@ fn main() {
     let llvm_linker_flags = tracked_env_var_os("LLVM_LINKER_FLAGS");
     if let Some(s) = llvm_linker_flags {
         for lib in s.into_string().unwrap().split_whitespace() {
-            if lib.starts_with("-l") {
-                println!("cargo:rustc-link-lib={}", &lib[2..]);
-            } else if lib.starts_with("-L") {
-                println!("cargo:rustc-link-search=native={}", &lib[2..]);
+            if let Some(stripped) = lib.strip_prefix("-l") {
+                println!("cargo:rustc-link-lib={}", stripped);
+            } else if let Some(stripped) = lib.strip_prefix("-L") {
+                println!("cargo:rustc-link-search=native={}", stripped);
             }
         }
     }

compiler/rustc_mir/src/transform/coverage/debug.rs

@@ -285,7 +285,7 @@ impl DebugCounters {
                 ),
             };
             counters
-                .insert(id.into(), DebugCounter::new(counter_kind.clone(), some_block_label))
+                .insert(id, DebugCounter::new(counter_kind.clone(), some_block_label))
                 .expect_none(
                     "attempt to add the same counter_kind to DebugCounters more than once",
                 );
@@ -340,7 +340,7 @@ impl DebugCounters {
         if self.some_counters.is_some() && (counter_format.block || !counter_format.id) {
             let counters = self.some_counters.as_ref().unwrap();
             if let Some(DebugCounter { some_block_label: Some(block_label), .. }) =
-                counters.get(&id.into())
+                counters.get(&id)
             {
                 return if counter_format.id {
                     format!("{}#{}", block_label, id.index())

compiler/rustc_mir/src/transform/early_otherwise_branch.rs

@@ -216,9 +216,10 @@ impl<'a, 'tcx> Helper<'a, 'tcx> {
         let discr = self.find_switch_discriminant_info(bb, switch)?;
 
         // go through each target, finding a discriminant read, and a switch
-        let results = discr.targets_with_values.iter().map(|(value, target)| {
-            self.find_discriminant_switch_pairing(&discr, target.clone(), value.clone())
-        });
+        let results = discr
+            .targets_with_values
+            .iter()
+            .map(|(value, target)| self.find_discriminant_switch_pairing(&discr, *target, *value));
 
         // if the optimization did not apply for one of the targets, then abort
         if results.clone().any(|x| x.is_none()) || results.len() == 0 {

compiler/rustc_mir_build/src/build/scope.rs

@@ -616,8 +616,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 debug!("stmt_expr Break val block_context.push(SubExpr)");
                 self.block_context.push(BlockFrame::SubExpr);
                 unpack!(block = self.into(destination, dest_scope, block, value));
-                dest_scope
-                    .map(|scope| self.unschedule_drop(scope, destination.as_local().unwrap()));
+                if let Some(scope) = dest_scope {
+                    self.unschedule_drop(scope, destination.as_local().unwrap())
+                };
                 self.block_context.pop();
             } else {
                 self.cfg.push_assign_unit(block, source_info, destination, self.hir.tcx())

compiler/rustc_session/src/session.rs

@@ -1109,10 +1109,7 @@ impl Session {
     }
 
     pub fn link_dead_code(&self) -> bool {
-        match self.opts.cg.link_dead_code {
-            Some(explicitly_set) => explicitly_set,
-            None => false,
-        }
+        self.opts.cg.link_dead_code.unwrap_or(false)
     }
 
     pub fn mark_attr_known(&self, attr: &Attribute) {

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1448,31 +1448,30 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             });
         };
 
-        typeck_results
+        if let Some(cause) = typeck_results
             .generator_interior_types
             .iter()
             .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty_matches(ty))
-            .map(|cause| {
-                // Check to see if any awaited expressions have the target type.
-                let from_awaited_ty = visitor
-                    .awaits
-                    .into_iter()
-                    .map(|id| hir.expect_expr(id))
-                    .find(|await_expr| {
-                        let ty = typeck_results.expr_ty_adjusted(&await_expr);
-                        debug!(
-                            "maybe_note_obligation_cause_for_async_await: await_expr={:?}",
-                            await_expr
-                        );
-                        ty_matches(ty)
-                    })
-                    .map(|expr| expr.span);
-                let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } =
-                    cause;
+        {
+            // Check to see if any awaited expressions have the target type.
+            let from_awaited_ty = visitor
+                .awaits
+                .into_iter()
+                .map(|id| hir.expect_expr(id))
+                .find(|await_expr| {
+                    let ty = typeck_results.expr_ty_adjusted(&await_expr);
+                    debug!(
+                        "maybe_note_obligation_cause_for_async_await: await_expr={:?}",
+                        await_expr
+                    );
+                    ty_matches(ty)
+                })
+                .map(|expr| expr.span);
+            let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;
 
-                interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span));
-                interior_extra_info = Some((*scope_span, *yield_span, *expr, from_awaited_ty));
-            });
+            interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span));
+            interior_extra_info = Some((*scope_span, *yield_span, *expr, from_awaited_ty));
+        };
 
         debug!(
             "maybe_note_obligation_cause_for_async_await: interior_or_upvar={:?} \

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

@@ -447,7 +447,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
                 nested.push(Obligation::new(
                     obligation.cause.clone(),
-                    obligation.param_env.clone(),
+                    obligation.param_env,
                     normalized_super_trait,
                 ));
             }
@@ -485,7 +485,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
                 nested.push(Obligation::new(
                     obligation.cause.clone(),
-                    obligation.param_env.clone(),
+                    obligation.param_env,
                     normalized_bound,
                 ));
             }

compiler/rustc_typeck/src/check/upvar.rs

@@ -297,17 +297,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                     closure_captures.insert(*var_hir_id, upvar_id);
 
-                    let new_capture_kind = if let Some(capture_kind) =
-                        upvar_capture_map.get(&upvar_id)
-                    {
-                        // upvar_capture_map only stores the UpvarCapture (CaptureKind),
-                        // so we create a fake capture info with no expression.
-                        let fake_capture_info =
-                            ty::CaptureInfo { expr_id: None, capture_kind: capture_kind.clone() };
-                        determine_capture_info(fake_capture_info, capture_info).capture_kind
-                    } else {
-                        capture_info.capture_kind
-                    };
+                    let new_capture_kind =
+                        if let Some(capture_kind) = upvar_capture_map.get(&upvar_id) {
+                            // upvar_capture_map only stores the UpvarCapture (CaptureKind),
+                            // so we create a fake capture info with no expression.
+                            let fake_capture_info =
+                                ty::CaptureInfo { expr_id: None, capture_kind: *capture_kind };
+                            determine_capture_info(fake_capture_info, capture_info).capture_kind
+                        } else {
+                            capture_info.capture_kind
+                        };
                     upvar_capture_map.insert(upvar_id, new_capture_kind);
                 }
             }

compiler/rustc_typeck/src/collect.rs

@@ -2141,13 +2141,8 @@ fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicat
             // * It must be an associated type for this trait (*not* a
             //   supertrait).
             if let ty::Projection(projection) = ty.kind() {
-                if projection.substs == trait_identity_substs
+                projection.substs == trait_identity_substs
                     && tcx.associated_item(projection.item_def_id).container.id() == def_id
-                {
-                    true
-                } else {
-                    false
-                }
             } else {
                 false
             }

src/bootstrap/dist.rs

@@ -1186,7 +1186,7 @@ pub fn sanitize_sh(path: &Path) -> String {
     return change_drive(unc_to_lfs(&path)).unwrap_or(path);
 
     fn unc_to_lfs(s: &str) -> &str {
-        if s.starts_with("//?/") { &s[4..] } else { s }
+        s.strip_prefix("//?/").unwrap_or(s)
     }
 
     fn change_drive(s: &str) -> Option<String> {

src/bootstrap/sanity.rs

@@ -159,11 +159,7 @@ pub fn check(build: &mut Build) {
             panic!("the iOS target is only supported on macOS");
         }
 
-        build
-            .config
-            .target_config
-            .entry(target.clone())
-            .or_insert(Target::from_triple(&target.triple));
+        build.config.target_config.entry(*target).or_insert(Target::from_triple(&target.triple));
 
         if target.contains("-none-") || target.contains("nvptx") {
             if build.no_std(*target) == Some(false) {
@@ -176,7 +172,7 @@ pub fn check(build: &mut Build) {
             // If this is a native target (host is also musl) and no musl-root is given,
             // fall back to the system toolchain in /usr before giving up
             if build.musl_root(*target).is_none() && build.config.build == *target {
-                let target = build.config.target_config.entry(target.clone()).or_default();
+                let target = build.config.target_config.entry(*target).or_default();
                 target.musl_root = Some("/usr".into());
             }
             match build.musl_libdir(*target) {

src/librustdoc/html/markdown.rs

@@ -139,9 +139,9 @@ fn map_line(s: &str) -> Line<'_> {
     let trimmed = s.trim();
     if trimmed.starts_with("##") {
         Line::Shown(Cow::Owned(s.replacen("##", "#", 1)))
-    } else if trimmed.starts_with("# ") {
+    } else if let Some(stripped) = trimmed.strip_prefix("# ") {
         // # text
-        Line::Hidden(&trimmed[2..])
+        Line::Hidden(&stripped)
     } else if trimmed == "#" {
         // We cannot handle '#text' because it could be #[attr].
         Line::Hidden("")

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -1012,15 +1012,14 @@ impl LinkCollector<'_, '_> {
         } else {
             // This is a bug.
             debug!("attempting to resolve item without parent module: {}", path_str);
-            let err_kind = ResolutionFailure::NoParentItem.into();
             resolution_failure(
                 self,
                 &item,
                 path_str,
                 disambiguator,
                 dox,
                 link_range,
-                smallvec![err_kind],
+                smallvec![ResolutionFailure::NoParentItem],
             );
             return None;
         };