Fix more clippy warnings

Fixes more of:

clippy::unused_unit
clippy::op_ref
clippy::useless_format
clippy::needless_return
clippy::useless_conversion
clippy::bind_instead_of_map
clippy::into_iter_on_ref
clippy::redundant_clone
clippy::nonminimal_bool
clippy::redundant_closure
clippy::option_as_ref_deref
clippy::len_zero
clippy::iter_cloned_collect
clippy::filter_next

src/librustc_ast/tokenstream.rs

@@ -392,7 +392,7 @@ impl TokenStream {
                         break;
                     }
                 }
-                token_trees = out.into_iter().map(|t| TokenTree::Token(t)).collect();
+                token_trees = out.into_iter().map(TokenTree::Token).collect();
                 if token_trees.len() != 1 {
                     debug!("break_tokens: broke {:?} to {:?}", tree, token_trees);
                 }

src/librustc_ast_lowering/expr.rs

@@ -1237,10 +1237,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
                                             ) => {
                                                 assert!(!*late);
                                                 let out_op_sp = if input { op_sp2 } else { op_sp };
-                                                let msg = &format!(
-                                                    "use `lateout` instead of \
-                                                     `out` to avoid conflict"
-                                                );
+                                                let msg = "use `lateout` instead of \
+                                                     `out` to avoid conflict";
                                                 err.span_help(out_op_sp, msg);
                                             }
                                             _ => {}

src/librustc_builtin_macros/asm.rs

@@ -457,7 +457,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, sp: Span, args: AsmArgs) -> P<ast
 
                 let mut chars = arg.format.ty.chars();
                 let mut modifier = chars.next();
-                if !chars.next().is_none() {
+                if chars.next().is_some() {
                     let span = arg
                         .format
                         .ty_span

src/librustc_codegen_ssa/mir/constant.rs

@@ -63,7 +63,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     .tcx()
                     .destructure_const(ty::ParamEnv::reveal_all().and(&c))
                     .fields
-                    .into_iter()
+                    .iter()
                     .map(|field| {
                         if let Some(prim) = field.val.try_to_scalar() {
                             let layout = bx.layout_of(field_ty);

src/librustc_errors/annotate_snippet_emitter_writer.rs

@@ -159,14 +159,10 @@ impl AnnotateSnippetEmitterWriter {
                             // FIXME(#59346): Not really sure when `fold` should be true or false
                             fold: false,
                             annotations: annotations
-                                .into_iter()
+                                .iter()
                                 .map(|annotation| SourceAnnotation {
                                     range: (annotation.start_col, annotation.end_col),
-                                    label: annotation
-                                        .label
-                                        .as_ref()
-                                        .map(|s| s.as_str())
-                                        .unwrap_or_default(),
+                                    label: annotation.label.as_deref().unwrap_or_default(),
                                     annotation_type: annotation_type_for_level(*level),
                                 })
                                 .collect(),

src/librustc_infer/infer/error_reporting/need_type_info.rs

@@ -550,7 +550,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let error_code = error_code.into();
         let mut err = self.tcx.sess.struct_span_err_with_code(
             local_visitor.target_span,
-            &format!("type annotations needed"),
+            "type annotations needed",
             error_code,
         );
 

src/librustc_infer/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -77,8 +77,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             }
             _ => {}
         }
-        let mut type_param_span: MultiSpan =
-            visitor.types.iter().cloned().collect::<Vec<_>>().into();
+        let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
         for &span in &visitor.types {
             type_param_span.push_span_label(
                 span,

src/librustc_lexer/src/lib.rs

@@ -187,9 +187,9 @@ pub fn strip_shebang(input: &str) -> Option<usize> {
             // Ok, this is a shebang but if the next non-whitespace token is `[` or maybe
             // a doc comment (due to `TokenKind::(Line,Block)Comment` ambiguity at lexer level),
             // then it may be valid Rust code, so consider it Rust code.
-            let next_non_whitespace_token = tokenize(input_tail).map(|tok| tok.kind).filter(|tok|
+            let next_non_whitespace_token = tokenize(input_tail).map(|tok| tok.kind).find(|tok|
                 !matches!(tok, TokenKind::Whitespace | TokenKind::LineComment | TokenKind::BlockComment { .. })
-            ).next();
+            );
             if next_non_whitespace_token != Some(TokenKind::OpenBracket) {
                 // No other choice than to consider this a shebang.
                 return Some(2 + first_line_tail.len());

src/librustc_mir/const_eval/eval_queries.rs

@@ -309,9 +309,7 @@ pub fn const_eval_raw_provider<'tcx>(
 
     let res = ecx.load_mir(cid.instance.def, cid.promoted);
     res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body))
-        .and_then(|place| {
-            Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
-        })
+        .map(|place| RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
         .map_err(|error| {
             let err = error_to_const_error(&ecx, error);
             // errors in statics are always emitted as fatal errors

src/librustc_mir/transform/check_packed_ref.rs

@@ -51,7 +51,7 @@ impl<'a, 'tcx> Visitor<'tcx> for PackedRefChecker<'a, 'tcx> {
                     lint_root,
                     source_info.span,
                     |lint| {
-                        lint.build(&format!("reference to packed field is unaligned",))
+                        lint.build("reference to packed field is unaligned")
                             .note(
                                 "fields of packed structs are not properly aligned, and creating \
                                 a misaligned reference is undefined behavior (even if that \

src/librustc_mir/transform/nrvo.rs

@@ -111,7 +111,7 @@ fn local_eligible_for_nrvo(body: &mut mir::Body<'_>) -> Option<Local> {
         copied_to_return_place = Some(returned_local);
     }
 
-    return copied_to_return_place;
+    copied_to_return_place
 }
 
 fn find_local_assigned_to_return_place(
@@ -136,7 +136,7 @@ fn find_local_assigned_to_return_place(
         }
     }
 
-    return None;
+    None
 }
 
 // If this statement is an assignment of an unprojected local to the return place,

src/librustc_mir/transform/simplify_try.rs

@@ -99,7 +99,7 @@ fn get_arm_identity_info<'a, 'tcx>(stmts: &'a [Statement<'tcx>]) -> Option<ArmId
     fn try_eat<'a, 'tcx>(
         stmt_iter: &mut StmtIter<'a, 'tcx>,
         test: impl Fn(&'a Statement<'tcx>) -> bool,
-        mut action: impl FnMut(usize, &'a Statement<'tcx>) -> (),
+        mut action: impl FnMut(usize, &'a Statement<'tcx>),
     ) {
         while stmt_iter.peek().map(|(_, stmt)| test(stmt)).unwrap_or(false) {
             let (idx, stmt) = stmt_iter.next().unwrap();
@@ -271,7 +271,7 @@ fn optimization_applies<'tcx>(
     }
 
     // Verify the assigment chain consists of the form b = a; c = b; d = c; etc...
-    if opt_info.field_tmp_assignments.len() == 0 {
+    if opt_info.field_tmp_assignments.is_empty() {
         trace!("NO: no assignments found");
     }
     let mut last_assigned_to = opt_info.field_tmp_assignments[0].1;

src/librustc_parse/lexer/mod.rs

@@ -401,7 +401,7 @@ impl<'a> StringReader<'a> {
         let content_end = suffix_start - BytePos(postfix_len);
         let id = self.symbol_from_to(content_start, content_end);
         self.validate_literal_escape(mode, content_start, content_end);
-        return (lit_kind, id);
+        (lit_kind, id)
     }
 
     pub fn pos(&self) -> BytePos {

src/librustc_parse/parser/diagnostics.rs

@@ -936,7 +936,7 @@ impl<'a> Parser<'a> {
         } else if !sm.is_multiline(self.prev_token.span.until(self.token.span)) {
             // The current token is in the same line as the prior token, not recoverable.
         } else if [token::Comma, token::Colon].contains(&self.token.kind)
-            && &self.prev_token.kind == &token::CloseDelim(token::Paren)
+            && self.prev_token.kind == token::CloseDelim(token::Paren)
         {
             // Likely typo: The current token is on a new line and is expected to be
             // `.`, `;`, `?`, or an operator after a close delimiter token.

src/librustc_parse/parser/mod.rs

@@ -193,7 +193,7 @@ impl TokenCursor {
                         tree,
                         self.stack.len()
                     );
-                    collecting.buf.push(tree.clone().into())
+                    collecting.buf.push(tree.clone())
                 }
             }
 
@@ -675,7 +675,7 @@ impl<'a> Parser<'a> {
                             // If this was a missing `@` in a binding pattern
                             // bail with a suggestion
                             // https://github.com/rust-lang/rust/issues/72373
-                            if self.prev_token.is_ident() && &self.token.kind == &token::DotDot {
+                            if self.prev_token.is_ident() && self.token.kind == token::DotDot {
                                 let msg = format!(
                                     "if you meant to bind the contents of \
                                     the rest of the array pattern into `{}`, use `@`",
@@ -1193,7 +1193,7 @@ impl<'a> Parser<'a> {
         let mut collected_tokens = if let Some(collecting) = self.token_cursor.collecting.take() {
             collecting.buf
         } else {
-            let msg = format!("our vector went away?");
+            let msg = "our vector went away?";
             debug!("collect_tokens: {}", msg);
             self.sess.span_diagnostic.delay_span_bug(self.token.span, &msg);
             // This can happen due to a bad interaction of two unrelated recovery mechanisms

src/librustc_passes/intrinsicck.rs

@@ -232,7 +232,7 @@ impl ExprVisitor<'tcx> {
         // size).
         if let Some((in_expr, Some(in_asm_ty))) = tied_input {
             if in_asm_ty != asm_ty {
-                let msg = &format!("incompatible types for asm inout argument");
+                let msg = "incompatible types for asm inout argument";
                 let mut err = self.tcx.sess.struct_span_err(vec![in_expr.span, expr.span], msg);
                 err.span_label(
                     in_expr.span,

src/librustdoc/html/sources.rs

@@ -126,7 +126,7 @@ impl<'a> SourceCollector<'a> {
             &self.scx.themes,
         );
         self.scx.fs.write(&cur, v.as_bytes())?;
-        self.scx.local_sources.insert(p.clone(), href);
+        self.scx.local_sources.insert(p, href);
         Ok(())
     }
 }

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -451,7 +451,7 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
                             ..
                         },
                     ..
-                })) => segments.first().and_then(|seg| Some(seg.ident.to_string())),
+                })) => segments.first().map(|seg| seg.ident.to_string()),
                 Some(hir::Node::Item(hir::Item {
                     ident, kind: hir::ItemKind::Enum(..), ..
                 }))