refactor: remove unnecessary variables

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -906,7 +906,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     if let hir::ExprKind::Closure(hir::Closure {
                         capture_clause: hir::CaptureBy::Ref,
                         ..
-                    }) = arg.kind {
+                    }) = arg.kind
+                    {
                         closure_span = Some(arg.span.shrink_to_lo());
                         break;
                     }

compiler/rustc_hir/src/hir.rs

@@ -1881,11 +1881,11 @@ pub enum ExprKind<'hir> {
     ///
     /// The `PathSegment` represents the method name and its generic arguments
     /// (within the angle brackets).
-    /// The first element of the `&[Expr]` is the expression that evaluates
+    /// The `&Expr` is the expression that evaluates
     /// to the object on which the method is being called on (the receiver),
-    /// and the remaining elements are the rest of the arguments.
+    /// and the `&[Expr]` is the rest of the arguments.
     /// Thus, `x.foo::<Bar, Baz>(a, b, c, d)` is represented as
-    /// `ExprKind::MethodCall(PathSegment { foo, [Bar, Baz] }, [x, a, b, c, d], span)`.
+    /// `ExprKind::MethodCall(PathSegment { foo, [Bar, Baz] }, x, [a, b, c, d], span)`.
     /// The final `Span` represents the span of the function and arguments
     /// (e.g. `foo::<Bar, Baz>(a, b, c, d)` in `x.foo::<Bar, Baz>(a, b, c, d)`
     ///

compiler/rustc_lint/src/array_into_iter.rs

@@ -61,7 +61,7 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
         }
 
         // We only care about method call expressions.
-        if let hir::ExprKind::MethodCall(call, receiver, ..) = &expr.kind {
+        if let hir::ExprKind::MethodCall(call, receiver_arg, ..) = &expr.kind {
             if call.ident.name != sym::into_iter {
                 return;
             }
@@ -75,7 +75,6 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
             };
 
             // As this is a method call expression, we have at least one argument.
-            let receiver_arg = receiver;
             let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
             let adjustments = cx.typeck_results().expr_adjustments(receiver_arg);
 

compiler/rustc_lint/src/methods.rs

@@ -63,15 +63,13 @@ impl<'tcx> LateLintPass<'tcx> for TemporaryCStringAsPtr {
         }
 
         match first_method_call(expr) {
-            Some((path, receiver)) if path.ident.name == sym::as_ptr => {
+            Some((path, unwrap_arg)) if path.ident.name == sym::as_ptr => {
-                let unwrap_arg = receiver;
                 let as_ptr_span = path.ident.span;
                 match first_method_call(unwrap_arg) {
                     Some((path, receiver))
                         if path.ident.name == sym::unwrap || path.ident.name == sym::expect =>
                     {
-                        let source_arg = receiver;
+                        lint_cstring_as_ptr(cx, as_ptr_span, receiver, unwrap_arg);
-                        lint_cstring_as_ptr(cx, as_ptr_span, source_arg, unwrap_arg);
                     }
                     _ => return,
                 }

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -267,7 +267,8 @@ impl<'tcx> Cx<'tcx> {
                 // When we apply adjustments to the receiver, use the span of
                 // the overall method call for better diagnostics. args[0]
                 // is guaranteed to exist, since a method call always has a receiver.
-                let old_adjustment_span = self.adjustment_span.replace((receiver.hir_id, expr_span));
+                let old_adjustment_span =
+                    self.adjustment_span.replace((receiver.hir_id, expr_span));
                 info!("Using method span: {:?}", expr.span);
                 let args = std::iter::once(receiver)
                     .chain(args.iter())

compiler/rustc_passes/src/liveness.rs

@@ -1041,10 +1041,11 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
 
             hir::ExprKind::MethodCall(.., receiver, ref args, _) => {
                 let succ = self.check_is_ty_uninhabited(expr, succ);
-                std::iter::once(receiver)
+                let succ = args
-                    .chain(args.iter())
+                    .iter()
                     .rev()
-                    .fold(succ, |succ, expr| self.propagate_through_expr(expr, succ))
+                    .fold(succ, |succ, expr| self.propagate_through_expr(expr, succ));
+                self.propagate_through_expr(receiver, succ)
             }
 
             hir::ExprKind::Tup(ref exprs) => self.propagate_through_exprs(exprs, succ),

compiler/rustc_typeck/src/check/demand.rs

@@ -770,16 +770,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     if let hir::ExprKind::MethodCall(ref segment, receiver, args, _) = expr.kind {
                         let clone_trait =
                             self.tcx.require_lang_item(LangItem::Clone, Some(segment.ident.span));
-                        if let (true, Some(true), sym::clone) = (
+                        if args.is_empty()
-                            args.is_empty(),
+                            && self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
-                            self.typeck_results.borrow().type_dependent_def_id(expr.hir_id).map(
                                 |did| {
                                     let ai = self.tcx.associated_item(did);
                                     ai.trait_container(self.tcx) == Some(clone_trait)
                                 },
-                            ),
+                            ) == Some(true)
-                            segment.ident.name,
+                            && segment.ident.name == sym::clone
-                        ) {
+                        {
                             // If this expression had a clone call when suggesting borrowing
                             // we want to suggest removing it because it'd now be unnecessary.
                             sugg_sp = receiver.span;

compiler/rustc_typeck/src/check/expr.rs

@@ -1195,14 +1195,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         expr: &'tcx hir::Expr<'tcx>,
         segment: &hir::PathSegment<'_>,
-        receiver: &'tcx hir::Expr<'tcx>,
+        rcvr: &'tcx hir::Expr<'tcx>,
         args: &'tcx [hir::Expr<'tcx>],
         expected: Expectation<'tcx>,
     ) -> Ty<'tcx> {
-        let rcvr = &receiver;
         let rcvr_t = self.check_expr(&rcvr);
         // no need to check for bot/err -- callee does that
-        let rcvr_t = self.structurally_resolved_type(receiver.span, rcvr_t);
+        let rcvr_t = self.structurally_resolved_type(rcvr.span, rcvr_t);
         let span = segment.ident.span;
 
         let method = match self.lookup_method(rcvr_t, segment, span, expr, rcvr, args) {
@@ -1219,9 +1218,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         span,
                         rcvr_t,
                         segment.ident,
-                        SelfSource::MethodCall(receiver),
+                        SelfSource::MethodCall(rcvr),
                         error,
-                        Some((receiver, args)),
+                        Some((rcvr, args)),
                     ) {
                         err.emit();
                     }

compiler/rustc_typeck/src/check/fn_ctxt/checks.rs

@@ -1913,14 +1913,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .enumerate()
             .filter(|(_, ty)| find_param_in_ty(**ty, param_to_point_at))
             .collect();
-        let args: Vec<&'tcx hir::Expr<'tcx>> = if let Some(receiver) = receiver {
-            std::iter::once(receiver).chain(args.iter()).collect()
-        } else {
-            args.iter().collect()
-        };
-
         // If there's one field that references the given generic, great!
-        if let [(idx, _)] = args_referencing_param.as_slice() && let Some(arg) = args.get(*idx) {
+        if let [(idx, _)] = args_referencing_param.as_slice()
+            && let Some(arg) = receiver
+                .map_or(args.get(*idx), |rcvr| if *idx == 0 { Some(rcvr) } else { args.get(*idx - 1) }) {
             error.obligation.cause.span = arg.span.find_ancestor_in_same_ctxt(error.obligation.cause.span).unwrap_or(arg.span);
             error.obligation.cause.map_code(|parent_code| {
                 ObligationCauseCode::FunctionArgumentObligation {

src/tools/clippy/clippy_lints/src/dereference.rs

@@ -798,57 +798,55 @@ fn walk_parents<'tcx>(
                     }),
                 ExprKind::MethodCall(_, receiver, args, _) => {
                     let id = cx.typeck_results().type_dependent_def_id(parent.hir_id).unwrap();
-                    std::iter::once(receiver)
+                    if receiver.hir_id == child_id {
-                        .chain(args.iter())
+                        // Check for calls to trait methods where the trait is implemented on a reference.
+                        // Two cases need to be handled:
+                        // * `self` methods on `&T` will never have auto-borrow
+                        // * `&self` methods on `&T` can have auto-borrow, but `&self` methods on `T` will take
+                        //   priority.
+                        if e.hir_id != child_id {
+                            return Some(Position::ReborrowStable(precedence))
+                        } else if let Some(trait_id) = cx.tcx.trait_of_item(id)
+                            && let arg_ty = cx.tcx.erase_regions(cx.typeck_results().expr_ty_adjusted(e))
+                            && let ty::Ref(_, sub_ty, _) = *arg_ty.kind()
+                            && let subs = match cx
+                                .typeck_results()
+                                .node_substs_opt(parent.hir_id)
+                                .and_then(|subs| subs.get(1..))
+                            {
+                                Some(subs) => cx.tcx.mk_substs(subs.iter().copied()),
+                                None => cx.tcx.mk_substs(std::iter::empty::<ty::subst::GenericArg<'_>>()),
+                            } && let impl_ty = if cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref() {
+                                // Trait methods taking `&self`
+                                sub_ty
+                            } else {
+                                // Trait methods taking `self`
+                                arg_ty
+                            } && impl_ty.is_ref()
+                            && cx.tcx.infer_ctxt().enter(|infcx|
+                                infcx
+                                    .type_implements_trait(trait_id, impl_ty, subs, cx.param_env)
+                                    .must_apply_modulo_regions()
+                            )
+                        {
+                            return Some(Position::MethodReceiverRefImpl)
+                        } else {
+                            return Some(Position::MethodReceiver)
+                        }
+                    }
+                    args.iter()
                         .position(|arg| arg.hir_id == child_id)
                         .map(|i| {
-                            if i == 0 {
+                            let ty = cx.tcx.fn_sig(id).skip_binder().inputs()[i + 1];
-                                // Check for calls to trait methods where the trait is implemented on a reference.
+                            if let ty::Param(param_ty) = ty.kind() {
-                                // Two cases need to be handled:
+                                needless_borrow_impl_arg_position(cx, parent, i + 1, *param_ty, e, precedence, msrv)
-                                // * `self` methods on `&T` will never have auto-borrow
+                            } else {
-                                // * `&self` methods on `&T` can have auto-borrow, but `&self` methods on `T` will take
+                                ty_auto_deref_stability(
-                                //   priority.
+                                    cx,
-                                if e.hir_id != child_id {
+                                    cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(id).input(i + 1)),
-                                Position::ReborrowStable(precedence)
+                                    precedence,
-                            } else if let Some(trait_id) = cx.tcx.trait_of_item(id)
-                                && let arg_ty = cx.tcx.erase_regions(cx.typeck_results().expr_ty_adjusted(e))
-                                && let ty::Ref(_, sub_ty, _) = *arg_ty.kind()
-                                && let subs = match cx
-                                    .typeck_results()
-                                    .node_substs_opt(parent.hir_id)
-                                    .and_then(|subs| subs.get(1..))
-                                {
-                                    Some(subs) => cx.tcx.mk_substs(subs.iter().copied()),
-                                    None => cx.tcx.mk_substs(std::iter::empty::<ty::subst::GenericArg<'_>>()),
-                                } && let impl_ty = if cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref() {
-                                    // Trait methods taking `&self`
-                                    sub_ty
-                                } else {
-                                    // Trait methods taking `self`
-                                    arg_ty
-                                } && impl_ty.is_ref()
-                                && cx.tcx.infer_ctxt().enter(|infcx|
-                                    infcx
-                                        .type_implements_trait(trait_id, impl_ty, subs, cx.param_env)
-                                        .must_apply_modulo_regions()
                                 )
-                            {
+                                .position_for_arg()
-                                Position::MethodReceiverRefImpl
-                            } else {
-                                Position::MethodReceiver
-                            }
-                            } else {
-                                let ty = cx.tcx.fn_sig(id).skip_binder().inputs()[i];
-                                if let ty::Param(param_ty) = ty.kind() {
-                                    needless_borrow_impl_arg_position(cx, parent, i, *param_ty, e, precedence, msrv)
-                                } else {
-                                    ty_auto_deref_stability(
-                                        cx,
-                                        cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(id).input(i)),
-                                        precedence,
-                                    )
-                                    .position_for_arg()
-                                }
                             }
                         })
                 },

src/tools/clippy/clippy_lints/src/infinite_iter.rs

@@ -59,7 +59,7 @@ impl<'tcx> LateLintPass<'tcx> for InfiniteIter {
             MaybeInfinite => (MAYBE_INFINITE_ITER, "possible infinite iteration detected"),
             Finite => {
                 return;
-            },
+            }
         };
         span_lint(cx, lint, expr.span, msg);
     }
@@ -229,11 +229,9 @@ fn complete_infinite_iter(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
                     return MaybeInfinite.and(is_infinite(cx, receiver));
                 }
             }
-            if method.ident.name == sym!(last) {
+            if method.ident.name == sym!(last) && args.is_empty() {
-                let not_double_ended = cx
+                let not_double_ended =
-                    .tcx
+                    cx.tcx.get_diagnostic_item(sym::DoubleEndedIterator).map_or(false, |id| {
-                    .get_diagnostic_item(sym::DoubleEndedIterator)
-                    .map_or(false, |id| {
                         !implements_trait(cx, cx.typeck_results().expr_ty(receiver), id, &[])
                     });
                 if not_double_ended {

src/tools/clippy/clippy_lints/src/len_zero.rs

@@ -370,7 +370,7 @@ fn check_for_is_empty<'tcx>(
 }
 
 fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>, op: &str, compare_to: u32) {
-    if let (&ExprKind::MethodCall(method_path, receiver, ..), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind) {
+    if let (&ExprKind::MethodCall(method_path, receiver, args, _), &ExprKind::Lit(ref lit)) = (&method.kind, &lit.kind) {
         // check if we are in an is_empty() method
         if let Some(name) = get_item_name(cx, method) {
             if name.as_str() == "is_empty" {
@@ -378,7 +378,7 @@ fn check_cmp(cx: &LateContext<'_>, span: Span, method: &Expr<'_>, lit: &Expr<'_>
             }
         }
 
-        check_len(cx, span, method_path.ident.name, receiver, &lit.node, op, compare_to);
+        check_len(cx, span, method_path.ident.name, receiver, args, &lit.node, op, compare_to);
     } else {
         check_empty_expr(cx, span, method, lit, op);
     }
@@ -389,6 +389,7 @@ fn check_len(
     span: Span,
     method_name: Symbol,
     receiver: &Expr<'_>,
+    args: &[Expr<'_>],
     lit: &LitKind,
     op: &str,
     compare_to: u32,
@@ -399,7 +400,7 @@ fn check_len(
             return;
         }
 
-        if method_name == sym::len && has_is_empty(cx, receiver) {
+        if method_name == sym::len && args.is_empty() && has_is_empty(cx, receiver) {
             let mut applicability = Applicability::MachineApplicable;
             span_lint_and_sugg(
                 cx,

src/tools/clippy/clippy_lints/src/methods/clone_on_copy.rs

@@ -21,10 +21,7 @@ pub(super) fn check(
     receiver: &Expr<'_>,
     args: &[Expr<'_>],
 ) {
-    let arg = match args {
+    let arg = if method_name == sym::clone && args.is_empty() { receiver } else { return };
-        [] if method_name == sym::clone => receiver,
-        _ => return,
-    };
     if cx
         .typeck_results()
         .type_dependent_def_id(expr.hir_id)

src/tools/clippy/clippy_lints/src/methods/clone_on_ref_ptr.rs

@@ -20,8 +20,7 @@ pub(super) fn check(
     if !(args.is_empty() && method_name == sym::clone) {
         return;
     }
-    let arg = receiver;
+    let obj_ty = cx.typeck_results().expr_ty(receiver).peel_refs();
-    let obj_ty = cx.typeck_results().expr_ty(arg).peel_refs();
 
     if let ty::Adt(_, subst) = obj_ty.kind() {
         let caller_type = if is_type_diagnostic_item(cx, obj_ty, sym::Rc) {
@@ -34,7 +33,7 @@ pub(super) fn check(
             return;
         };
 
-        let snippet = snippet_with_macro_callsite(cx, arg.span, "..");
+        let snippet = snippet_with_macro_callsite(cx, receiver.span, "..");
 
         span_lint_and_sugg(
             cx,

src/tools/clippy/clippy_lints/src/methods/mod.rs

@@ -3381,7 +3381,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
 impl Methods {
     #[allow(clippy::too_many_lines)]
     fn check_methods<'tcx>(&self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some((name, recv, [args @ ..], span)) = method_call(expr) {
+        if let Some((name, recv, args, span)) = method_call(expr) {
             match (name, args) {
                 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
                     zst_offset::check(cx, expr, recv);
@@ -3485,7 +3485,7 @@ impl Methods {
                     }
                 },
                 ("last", []) | ("skip", [_]) => {
-                    if let Some((name2, recv2, [args2 @ ..], _span2)) = method_call(recv) {
+                    if let Some((name2, recv2, args2, _span2)) = method_call(recv) {
                         if let ("cloned", []) = (name2, args2) {
                             iter_overeager_cloned::check(cx, expr, recv, recv2, false, false);
                         }
@@ -3500,7 +3500,7 @@ impl Methods {
                     } else {
                         map_err_ignore::check(cx, expr, m_arg);
                     }
-                    if let Some((name, recv2, [args @ ..], span2)) = method_call(recv) {
+                    if let Some((name, recv2, args, span2)) = method_call(recv) {
                         match (name, args) {
                             ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, self.msrv),
                             ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, self.msrv),
@@ -3520,7 +3520,7 @@ impl Methods {
                     manual_ok_or::check(cx, expr, recv, def, map);
                 },
                 ("next", []) => {
-                    if let Some((name2, recv2, [args2 @ ..], _)) = method_call(recv) {
+                    if let Some((name2, recv2, args2, _)) = method_call(recv) {
                         match (name2, args2) {
                             ("cloned", []) => iter_overeager_cloned::check(cx, expr, recv, recv2, false, false),
                             ("filter", [arg]) => filter_next::check(cx, expr, recv2, arg),
@@ -3593,7 +3593,7 @@ impl Methods {
                 },
                 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
                 ("take", [_arg]) => {
-                    if let Some((name2, recv2, [args2 @ ..], _span2)) = method_call(recv) {
+                    if let Some((name2, recv2, args2, _span2)) = method_call(recv) {
                         if let ("cloned", []) = (name2, args2) {
                             iter_overeager_cloned::check(cx, expr, recv, recv2, false, false);
                         }

src/tools/clippy/clippy_lints/src/minmax.rs

@@ -109,14 +109,12 @@ fn fetch_const<'a>(
     args: &'a [Expr<'a>],
     m: MinMax,
 ) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
-    if (receiver.is_some() && args.len() != 1) || (receiver.is_none() && args.len() != 2) {
+    let mut args = receiver.into_iter().chain(args.into_iter());
+    let arg0 = args.next()?;
+    let arg1 = args.next()?;
+    if args.next().is_some() {
         return None;
     }
-    let (arg0, arg1) = if let Some(receiver) = receiver {
-        (receiver, &args[0])
-    } else {
-        (&args[0], &args[1])
-    };
     constant_simple(cx, cx.typeck_results(), arg0).map_or_else(
         || constant_simple(cx, cx.typeck_results(), arg1).map(|c| (m, c, arg0)),
         |c| {

src/tools/clippy/clippy_lints/src/unused_peekable.rs

@@ -150,7 +150,7 @@ impl<'tcx> Visitor<'_> for PeekableVisitor<'_, 'tcx> {
                                     ..
                                 },
                                 self_arg,
-                                [remaining_args @ ..],
+                                remaining_args,
                                 _,
                             ) => {
                                 let method_name = method_name_ident.name.as_str();