more clippy fixes

use is_empty() instead of len comparison (clippy::len_zero)
use if let instead of while let loop that never loops (clippy::never_loop)
remove redundant returns (clippy::needless_return)
remove redundant closures (clippy::redundant_closure)
use if let instead of match and wildcard pattern (clippy::single_match)
don't repeat field names redundantly (clippy::redundant_field_names)

src/librustc_interface/passes.rs

@@ -711,7 +711,7 @@ impl<'tcx> QueryContext<'tcx> {
     }
 
     pub fn print_stats(&mut self) {
-        self.enter(|tcx| ty::query::print_stats(tcx))
+        self.enter(ty::query::print_stats)
     }
 }
 

src/librustc_mir/interpret/terminator.rs

@@ -30,7 +30,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 trace!("SwitchInt({:?})", *discr);
 
                 // Branch to the `otherwise` case by default, if no match is found.
-                assert!(targets.len() > 0);
+                assert!(!targets.is_empty());
                 let mut target_block = targets[targets.len() - 1];
 
                 for (index, &const_int) in values.iter().enumerate() {

src/librustc_save_analysis/lib.rs

@@ -591,7 +591,7 @@ impl<'l, 'tcx> SaveContext<'l, 'tcx> {
                 Some(Data::RefData(Ref {
                     kind: RefKind::Function,
                     span,
-                    ref_id: def_id.or(decl_id).map(id_from_def_id).unwrap_or_else(|| null_id()),
+                    ref_id: def_id.or(decl_id).map(id_from_def_id).unwrap_or_else(null_id),
                 }))
             }
             ast::ExprKind::Path(_, ref path) => {

src/librustc_session/config.rs

@@ -1650,7 +1650,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
 
     check_thread_count(&debugging_opts, error_format);
 
-    let incremental = cg.incremental.as_ref().map(|m| PathBuf::from(m));
+    let incremental = cg.incremental.as_ref().map(PathBuf::from);
 
     if debugging_opts.profile && incremental.is_some() {
         early_error(

src/librustc_target/spec/i686_apple_darwin.rs

@@ -16,7 +16,7 @@ pub fn target() -> TargetResult {
     let llvm_target = super::apple_base::macos_llvm_target(&arch);
 
     Ok(Target {
-        llvm_target: llvm_target,
+        llvm_target,
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),

src/librustc_target/spec/x86_64_apple_darwin.rs

@@ -16,7 +16,7 @@ pub fn target() -> TargetResult {
     let llvm_target = super::apple_base::macos_llvm_target(&arch);
 
     Ok(Target {
-        llvm_target: llvm_target,
+        llvm_target,
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
         target_c_int_width: "32".to_string(),

src/librustdoc/clean/auto_trait.rs

@@ -497,11 +497,8 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                     // of the type.
                     // Therefore, we make sure that we never add a ?Sized
                     // bound for projections
-                    match &ty {
-                        &Type::QPath { .. } => {
-                            has_sized.insert(ty.clone());
-                        }
-                        _ => {}
+                    if let Type::QPath { .. } = ty {
+                        has_sized.insert(ty.clone());
                     }
 
                     if bounds.is_empty() {

src/librustdoc/clean/mod.rs

@@ -521,11 +521,8 @@ impl<'tcx> Clean<Option<WherePredicate>>
     fn clean(&self, cx: &DocContext<'_>) -> Option<WherePredicate> {
         let ty::OutlivesPredicate(ref a, ref b) = *self;
 
-        match (a, b) {
-            (ty::ReEmpty(_), ty::ReEmpty(_)) => {
-                return None;
-            }
-            _ => {}
+        if let (ty::ReEmpty(_), ty::ReEmpty(_)) = (a, b) {
+            return None;
         }
 
         Some(WherePredicate::RegionPredicate {
@@ -539,9 +536,8 @@ impl<'tcx> Clean<Option<WherePredicate>> for ty::OutlivesPredicate<Ty<'tcx>, ty:
     fn clean(&self, cx: &DocContext<'_>) -> Option<WherePredicate> {
         let ty::OutlivesPredicate(ref ty, ref lt) = *self;
 
-        match lt {
-            ty::ReEmpty(_) => return None,
-            _ => {}
+        if let ty::ReEmpty(_) = lt {
+            return None;
         }
 
         Some(WherePredicate::BoundPredicate {
@@ -2239,15 +2235,12 @@ impl Clean<Vec<Item>> for doctree::Import<'_> {
         } else {
             let name = self.name;
             if !please_inline {
-                match path.res {
-                    Res::Def(DefKind::Mod, did) => {
-                        if !did.is_local() && did.index == CRATE_DEF_INDEX {
-                            // if we're `pub use`ing an extern crate root, don't inline it unless we
-                            // were specifically asked for it
-                            denied = true;
-                        }
+                if let Res::Def(DefKind::Mod, did) = path.res {
+                    if !did.is_local() && did.index == CRATE_DEF_INDEX {
+                        // if we're `pub use`ing an extern crate root, don't inline it unless we
+                        // were specifically asked for it
+                        denied = true;
                     }
-                    _ => {}
                 }
             }
             if !denied {
@@ -2426,10 +2419,9 @@ impl From<GenericBound> for SimpleBound {
             GenericBound::TraitBound(t, mod_) => match t.trait_ {
                 Type::ResolvedPath { path, param_names, .. } => SimpleBound::TraitBound(
                     path.segments,
-                    param_names.map_or_else(
-                        || Vec::new(),
-                        |v| v.iter().map(|p| SimpleBound::from(p.clone())).collect(),
-                    ),
+                    param_names.map_or_else(Vec::new, |v| {
+                        v.iter().map(|p| SimpleBound::from(p.clone())).collect()
+                    }),
                     t.generic_params,
                     mod_,
                 ),

src/librustdoc/clean/utils.rs

@@ -121,7 +121,7 @@ pub fn external_generic_args(
     let args: Vec<_> = substs
         .iter()
         .filter_map(|kind| match kind.unpack() {
-            GenericArgKind::Lifetime(lt) => lt.clean(cx).map(|lt| GenericArg::Lifetime(lt)),
+            GenericArgKind::Lifetime(lt) => lt.clean(cx).map(GenericArg::Lifetime),
             GenericArgKind::Type(_) if skip_self => {
                 skip_self = false;
                 None
@@ -198,27 +198,24 @@ pub fn get_real_types(
         }) {
             let bounds = where_pred.get_bounds().unwrap_or_else(|| &[]);
             for bound in bounds.iter() {
-                match *bound {
-                    GenericBound::TraitBound(ref poly_trait, _) => {
-                        for x in poly_trait.generic_params.iter() {
-                            if !x.is_type() {
-                                continue;
-                            }
-                            if let Some(ty) = x.get_type() {
-                                let adds = get_real_types(generics, &ty, cx, recurse + 1);
-                                if !adds.is_empty() {
-                                    res.extend(adds);
-                                } else if !ty.is_full_generic() {
-                                    if let Some(did) = ty.def_id() {
-                                        if let Some(kind) = cx.tcx.def_kind(did).clean(cx) {
-                                            res.insert((ty, kind));
-                                        }
+                if let GenericBound::TraitBound(ref poly_trait, _) = *bound {
+                    for x in poly_trait.generic_params.iter() {
+                        if !x.is_type() {
+                            continue;
+                        }
+                        if let Some(ty) = x.get_type() {
+                            let adds = get_real_types(generics, &ty, cx, recurse + 1);
+                            if !adds.is_empty() {
+                                res.extend(adds);
+                            } else if !ty.is_full_generic() {
+                                if let Some(did) = ty.def_id() {
+                                    if let Some(kind) = cx.tcx.def_kind(did).clean(cx) {
+                                        res.insert((ty, kind));
                                     }
                                 }
                             }
                         }
                     }
-                    _ => {}
                 }
             }
         }

src/librustdoc/html/markdown.rs

@@ -448,7 +448,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for SummaryLine<'a, I> {
         if !self.started {
             self.started = true;
         }
-        while let Some(event) = self.inner.next() {
+        if let Some(event) = self.inner.next() {
             let mut is_start = true;
             let is_allowed_tag = match event {
                 Event::Start(Tag::CodeBlock(_)) | Event::End(Tag::CodeBlock(_)) => {
@@ -944,75 +944,70 @@ crate fn rust_code_blocks(md: &str) -> Vec<RustCodeBlock> {
     let mut p = Parser::new_ext(md, opts()).into_offset_iter();
 
     while let Some((event, offset)) = p.next() {
-        match event {
-            Event::Start(Tag::CodeBlock(syntax)) => {
-                let (syntax, code_start, code_end, range, is_fenced) = match syntax {
-                    CodeBlockKind::Fenced(syntax) => {
-                        let syntax = syntax.as_ref();
-                        let lang_string = if syntax.is_empty() {
-                            LangString::all_false()
-                        } else {
-                            LangString::parse(&*syntax, ErrorCodes::Yes, false)
-                        };
-                        if !lang_string.rust {
+        if let Event::Start(Tag::CodeBlock(syntax)) = event {
+            let (syntax, code_start, code_end, range, is_fenced) = match syntax {
+                CodeBlockKind::Fenced(syntax) => {
+                    let syntax = syntax.as_ref();
+                    let lang_string = if syntax.is_empty() {
+                        LangString::all_false()
+                    } else {
+                        LangString::parse(&*syntax, ErrorCodes::Yes, false)
+                    };
+                    if !lang_string.rust {
+                        continue;
+                    }
+                    let syntax = if syntax.is_empty() { None } else { Some(syntax.to_owned()) };
+                    let (code_start, mut code_end) = match p.next() {
+                        Some((Event::Text(_), offset)) => (offset.start, offset.end),
+                        Some((_, sub_offset)) => {
+                            let code = Range { start: sub_offset.start, end: sub_offset.start };
+                            code_blocks.push(RustCodeBlock {
+                                is_fenced: true,
+                                range: offset,
+                                code,
+                                syntax,
+                            });
                             continue;
                         }
-                        let syntax = if syntax.is_empty() { None } else { Some(syntax.to_owned()) };
-                        let (code_start, mut code_end) = match p.next() {
-                            Some((Event::Text(_), offset)) => (offset.start, offset.end),
-                            Some((_, sub_offset)) => {
-                                let code = Range { start: sub_offset.start, end: sub_offset.start };
-                                code_blocks.push(RustCodeBlock {
-                                    is_fenced: true,
-                                    range: offset,
-                                    code,
-                                    syntax,
-                                });
-                                continue;
-                            }
-                            None => {
-                                let code = Range { start: offset.end, end: offset.end };
-                                code_blocks.push(RustCodeBlock {
-                                    is_fenced: true,
-                                    range: offset,
-                                    code,
-                                    syntax,
-                                });
-                                continue;
-                            }
-                        };
-                        while let Some((Event::Text(_), offset)) = p.next() {
-                            code_end = offset.end;
+                        None => {
+                            let code = Range { start: offset.end, end: offset.end };
+                            code_blocks.push(RustCodeBlock {
+                                is_fenced: true,
+                                range: offset,
+                                code,
+                                syntax,
+                            });
+                            continue;
                         }
-                        (syntax, code_start, code_end, offset, true)
+                    };
+                    while let Some((Event::Text(_), offset)) = p.next() {
+                        code_end = offset.end;
                     }
-                    CodeBlockKind::Indented => {
-                        // The ending of the offset goes too far sometime so we reduce it by one in
-                        // these cases.
-                        if offset.end > offset.start
-                            && md.get(offset.end..=offset.end) == Some(&"\n")
-                        {
-                            (
-                                None,
-                                offset.start,
-                                offset.end,
-                                Range { start: offset.start, end: offset.end - 1 },
-                                false,
-                            )
-                        } else {
-                            (None, offset.start, offset.end, offset, false)
-                        }
+                    (syntax, code_start, code_end, offset, true)
+                }
+                CodeBlockKind::Indented => {
+                    // The ending of the offset goes too far sometime so we reduce it by one in
+                    // these cases.
+                    if offset.end > offset.start && md.get(offset.end..=offset.end) == Some(&"\n") {
+                        (
+                            None,
+                            offset.start,
+                            offset.end,
+                            Range { start: offset.start, end: offset.end - 1 },
+                            false,
+                        )
+                    } else {
+                        (None, offset.start, offset.end, offset, false)
                     }
-                };
+                }
+            };
 
-                code_blocks.push(RustCodeBlock {
-                    is_fenced,
-                    range,
-                    code: Range { start: code_start, end: code_end },
-                    syntax,
-                });
-            }
-            _ => (),
+            code_blocks.push(RustCodeBlock {
+                is_fenced,
+                range,
+                code: Range { start: code_start, end: code_end },
+                syntax,
+            });
         }
     }
 

src/librustdoc/html/render.rs

@@ -782,7 +782,7 @@ themePicker.onblur = handleThemeButtonsBlur;
                         .split('"')
                         .next()
                         .map(|s| s.to_owned())
-                        .unwrap_or_else(|| String::new()),
+                        .unwrap_or_else(String::new),
                 );
             }
         }
@@ -2158,7 +2158,7 @@ fn item_module(w: &mut Buffer, cx: &Context, item: &clean::Item, items: &[clean:
                     docs = MarkdownSummaryLine(doc_value, &myitem.links()).to_string(),
                     class = myitem.type_(),
                     add = add,
-                    stab = stab.unwrap_or_else(|| String::new()),
+                    stab = stab.unwrap_or_else(String::new),
                     unsafety_flag = unsafety_flag,
                     href = item_path(myitem.type_(), myitem.name.as_ref().unwrap()),
                     title = [full_path(cx, myitem), myitem.type_().to_string()]
@@ -4593,12 +4593,9 @@ fn collect_paths_for_type(first_ty: clean::Type) -> Vec<String> {
                 let get_extern = || cache.external_paths.get(&did).map(|s| s.0.clone());
                 let fqp = cache.exact_paths.get(&did).cloned().or_else(get_extern);
 
-                match fqp {
-                    Some(path) => {
-                        out.push(path.join("::"));
-                    }
-                    _ => {}
-                };
+                if let Some(path) = fqp {
+                    out.push(path.join("::"));
+                }
             }
             clean::Type::Tuple(tys) => {
                 work.extend(tys.into_iter());

src/librustdoc/html/render/cache.rs

@@ -590,7 +590,7 @@ fn build_index(krate: &clean::Crate, cache: &mut Cache) -> String {
     for item in search_index {
         item.parent_idx = item.parent.and_then(|defid| {
             if defid_to_pathid.contains_key(&defid) {
-                defid_to_pathid.get(&defid).map(|x| *x)
+                defid_to_pathid.get(&defid).copied()
             } else {
                 let pathid = lastpathid;
                 defid_to_pathid.insert(defid, pathid);

src/libstd/io/stdio.rs

@@ -496,7 +496,7 @@ pub fn stdout() -> Stdout {
         unsafe {
             let ret = Arc::new(ReentrantMutex::new(RefCell::new(LineWriter::new(stdout))));
             ret.init();
-            return ret;
+            ret
         }
     }
 }
@@ -664,7 +664,7 @@ pub fn stderr() -> Stderr {
             *INSTANCE.lock().borrow_mut() = Maybe::Real(stderr);
         }
     });
-    return Stderr { inner: &INSTANCE };
+    Stderr { inner: &INSTANCE }
 }
 
 impl Stderr {

src/libstd/sys/unix/process/process_unix.rs

@@ -72,7 +72,7 @@ impl Command {
             }
         };
 
-        let mut p = Process { pid: pid, status: None };
+        let mut p = Process { pid, status: None };
         drop(output);
         let mut bytes = [0; 8];