Separate the receiver from arguments in HIR

compiler/rustc_ast_lowering/src/expr.rs

@@ -68,10 +68,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         ParenthesizedGenericArgs::Err,
                         ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                     ));
-                    let args = self.arena.alloc_from_iter(
-                        [&*receiver].into_iter().chain(args.iter()).map(|x| self.lower_expr_mut(x)),
-                    );
-                    hir::ExprKind::MethodCall(hir_seg, args, self.lower_span(span))
+                    let receiver = self.lower_expr(receiver);
+                    let args =
+                        self.arena.alloc_from_iter(args.iter().map(|x| self.lower_expr_mut(x)));
+                    hir::ExprKind::MethodCall(hir_seg, receiver, args, self.lower_span(span))
                 }
                 ExprKind::Binary(binop, ref lhs, ref rhs) => {
                     let binop = self.lower_binop(binop);

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -711,8 +711,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                             Applicability::MachineApplicable,
                         );
                         self.suggested = true;
-                    } else if let hir::ExprKind::MethodCall(_path, args @ [_, ..], sp) = expr.kind
-                        && let hir::ExprKind::Index(val, index) = args[0].kind
+                    } else if let hir::ExprKind::MethodCall(_path, receiver, _, sp) = expr.kind
+                        && let hir::ExprKind::Index(val, index) = receiver.kind
                         && expr.span == self.assign_span
                     {
                         // val[index].path(args..);
@@ -724,7 +724,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                                     ".get_mut(".to_string(),
                                 ),
                                 (
-                                    index.span.shrink_to_hi().with_hi(args[0].span.hi()),
+                                    index.span.shrink_to_hi().with_hi(receiver.span.hi()),
                                     ").map(|val| val".to_string(),
                                 ),
                                 (sp.shrink_to_hi(), ")".to_string()),
@@ -911,11 +911,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                                                         [
                                                             Expr {
                                                                 kind:
-                                                                    MethodCall(
-                                                                        path_segment,
-                                                                        _args,
-                                                                        span,
-                                                                    ),
+                                                                    MethodCall(path_segment, _, _, span),
                                                                 hir_id,
                                                                 ..
                                                             },

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -900,14 +900,13 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         let mut closure_span = None::<rustc_span::Span>;
         match expr.kind {
             hir::ExprKind::MethodCall(.., args, _) => {
-                // only the first closre parameter of the method. args[0] is MethodCall PathSegment
-                for i in 1..args.len() {
+                for arg in args {
                     if let hir::ExprKind::Closure(hir::Closure {
                         capture_clause: hir::CaptureBy::Ref,
                         ..
-                    }) = args[i].kind
+                    }) = arg.kind
                     {
-                        closure_span = Some(args[i].span.shrink_to_lo());
+                        closure_span = Some(arg.span.shrink_to_lo());
                         break;
                     }
                 }

compiler/rustc_hir/src/hir.rs

@@ -1881,19 +1881,19 @@ 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)`
     ///
     /// To resolve the called method to a `DefId`, call [`type_dependent_def_id`] with
     /// the `hir_id` of the `MethodCall` node itself.
     ///
     /// [`type_dependent_def_id`]: ../../rustc_middle/ty/struct.TypeckResults.html#method.type_dependent_def_id
-    MethodCall(&'hir PathSegment<'hir>, &'hir [Expr<'hir>], Span),
+    MethodCall(&'hir PathSegment<'hir>, &'hir Expr<'hir>, &'hir [Expr<'hir>], Span),
     /// A tuple (e.g., `(a, b, c, d)`).
     Tup(&'hir [Expr<'hir>]),
     /// A binary operation (e.g., `a + b`, `a * b`).
@@ -3497,8 +3497,8 @@ mod size_asserts {
     // These are in alphabetical order, which is easy to maintain.
     static_assert_size!(Block<'_>, 48);
     static_assert_size!(Body<'_>, 32);
-    static_assert_size!(Expr<'_>, 56);
-    static_assert_size!(ExprKind<'_>, 40);
+    static_assert_size!(Expr<'_>, 64);
+    static_assert_size!(ExprKind<'_>, 48);
     static_assert_size!(FnDecl<'_>, 40);
     static_assert_size!(ForeignItem<'_>, 72);
     static_assert_size!(ForeignItemKind<'_>, 40);

compiler/rustc_hir/src/intravisit.rs

@@ -1094,8 +1094,9 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
             visitor.visit_expr(callee_expression);
             walk_list!(visitor, visit_expr, arguments);
         }
-        ExprKind::MethodCall(ref segment, arguments, _) => {
+        ExprKind::MethodCall(ref segment, receiver, arguments, _) => {
             visitor.visit_path_segment(expression.span, segment);
+            visitor.visit_expr(receiver);
             walk_list!(visitor, visit_expr, arguments);
         }
         ExprKind::Binary(_, ref left_expression, ref right_expression) => {

compiler/rustc_hir_pretty/src/lib.rs

@@ -1181,9 +1181,14 @@ impl<'a> State<'a> {
         self.print_call_post(args)
     }
 
-    fn print_expr_method_call(&mut self, segment: &hir::PathSegment<'_>, args: &[hir::Expr<'_>]) {
-        let base_args = &args[1..];
-        self.print_expr_maybe_paren(&args[0], parser::PREC_POSTFIX);
+    fn print_expr_method_call(
+        &mut self,
+        segment: &hir::PathSegment<'_>,
+        receiver: &hir::Expr<'_>,
+        args: &[hir::Expr<'_>],
+    ) {
+        let base_args = args;
+        self.print_expr_maybe_paren(&receiver, parser::PREC_POSTFIX);
         self.word(".");
         self.print_ident(segment.ident);
 
@@ -1394,8 +1399,8 @@ impl<'a> State<'a> {
             hir::ExprKind::Call(func, args) => {
                 self.print_expr_call(func, args);
             }
-            hir::ExprKind::MethodCall(segment, args, _) => {
-                self.print_expr_method_call(segment, args);
+            hir::ExprKind::MethodCall(segment, receiver, args, _) => {
+                self.print_expr_method_call(segment, receiver, args);
             }
             hir::ExprKind::Binary(op, lhs, rhs) => {
                 self.print_expr_binary(op, lhs, rhs);
@@ -2413,9 +2418,9 @@ fn contains_exterior_struct_lit(value: &hir::Expr<'_>) -> bool {
             contains_exterior_struct_lit(x)
         }
 
-        hir::ExprKind::MethodCall(.., exprs, _) => {
+        hir::ExprKind::MethodCall(_, receiver, ..) => {
             // `X { y: 1 }.bar(...)`
-            contains_exterior_struct_lit(&exprs[0])
+            contains_exterior_struct_lit(receiver)
         }
 
         _ => false,

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -901,7 +901,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                     }
                 }
             }
-            hir::ExprKind::MethodCall(segment, _, _) => {
+            hir::ExprKind::MethodCall(segment, ..) => {
                 if let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id) {
                     let generics = tcx.generics_of(def_id);
                     let insertable: Option<_> = try {
@@ -1132,7 +1132,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
                 let generic_args = &generics.own_substs_no_defaults(tcx, substs)
                     [generics.own_counts().lifetimes..];
                 let span = match expr.kind {
-                    ExprKind::MethodCall(path, _, _) => path.ident.span,
+                    ExprKind::MethodCall(path, ..) => path.ident.span,
                     _ => expr.span,
                 };
 
@@ -1181,20 +1181,20 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
             })
             .any(|generics| generics.has_impl_trait())
         };
-        if let ExprKind::MethodCall(path, args, span) = expr.kind
+        if let ExprKind::MethodCall(path, receiver, args, span) = expr.kind
             && let Some(substs) = self.node_substs_opt(expr.hir_id)
             && substs.iter().any(|arg| self.generic_arg_contains_target(arg))
             && let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id)
             && self.infcx.tcx.trait_of_item(def_id).is_some()
             && !has_impl_trait(def_id)
         {
             let successor =
-                args.get(1).map_or_else(|| (")", span.hi()), |arg| (", ", arg.span.lo()));
+                args.get(0).map_or_else(|| (")", span.hi()), |arg| (", ", arg.span.lo()));
             let substs = self.infcx.resolve_vars_if_possible(substs);
             self.update_infer_source(InferSource {
                 span: path.ident.span,
                 kind: InferSourceKind::FullyQualifiedMethodCall {
-                    receiver: args.first().unwrap(),
+                    receiver,
                     successor,
                     substs,
                     def_id,

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, args, _) = &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 = &args[0];
             let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
             let adjustments = cx.typeck_results().expr_adjustments(receiver_arg);
 

compiler/rustc_lint/src/builtin.rs

@@ -2412,13 +2412,13 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
                         _ => {}
                     }
                 }
-            } else if let hir::ExprKind::MethodCall(_, ref args, _) = expr.kind {
+            } else if let hir::ExprKind::MethodCall(_, receiver, ..) = expr.kind {
                 // Find problematic calls to `MaybeUninit::assume_init`.
                 let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
                 if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
                     // This is a call to *some* method named `assume_init`.
                     // See if the `self` parameter is one of the dangerous constructors.
-                    if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
+                    if let hir::ExprKind::Call(ref path_expr, _) = receiver.kind {
                         if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
                             let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
                             match cx.tcx.get_diagnostic_name(def_id) {

compiler/rustc_lint/src/internal.rs

@@ -51,7 +51,7 @@ fn typeck_results_of_method_fn<'tcx>(
     expr: &Expr<'_>,
 ) -> Option<(Span, DefId, ty::subst::SubstsRef<'tcx>)> {
     match expr.kind {
-        ExprKind::MethodCall(segment, _, _)
+        ExprKind::MethodCall(segment, ..)
             if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) =>
         {
             Some((segment.ident.span, def_id, cx.typeck_results().node_substs(expr.hir_id)))

compiler/rustc_lint/src/methods.rs

@@ -44,9 +44,13 @@ fn in_macro(span: Span) -> bool {
 
 fn first_method_call<'tcx>(
     expr: &'tcx Expr<'tcx>,
-) -> Option<(&'tcx PathSegment<'tcx>, &'tcx [Expr<'tcx>])> {
-    if let ExprKind::MethodCall(path, args, _) = &expr.kind {
-        if args.iter().any(|e| e.span.from_expansion()) { None } else { Some((path, *args)) }
+) -> Option<(&'tcx PathSegment<'tcx>, &'tcx Expr<'tcx>)> {
+    if let ExprKind::MethodCall(path, receiver, args, ..) = &expr.kind {
+        if args.iter().any(|e| e.span.from_expansion()) || receiver.span.from_expansion() {
+            None
+        } else {
+            Some((path, *receiver))
+        }
     } else {
         None
     }
@@ -59,15 +63,13 @@ impl<'tcx> LateLintPass<'tcx> for TemporaryCStringAsPtr {
         }
 
         match first_method_call(expr) {
-            Some((path, args)) if path.ident.name == sym::as_ptr => {
-                let unwrap_arg = &args[0];
+            Some((path, unwrap_arg)) if path.ident.name == sym::as_ptr => {
                 let as_ptr_span = path.ident.span;
                 match first_method_call(unwrap_arg) {
-                    Some((path, args))
+                    Some((path, receiver))
                         if path.ident.name == sym::unwrap || path.ident.name == sym::expect =>
                     {
-                        let source_arg = &args[0];
-                        lint_cstring_as_ptr(cx, as_ptr_span, source_arg, unwrap_arg);
+                        lint_cstring_as_ptr(cx, as_ptr_span, receiver, unwrap_arg);
                     }
                     _ => return,
                 }

compiler/rustc_lint/src/noop_method_call.rs

@@ -41,7 +41,7 @@ declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL]);
 impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         // We only care about method calls.
-        let ExprKind::MethodCall(call, elements, _) = &expr.kind else {
+        let ExprKind::MethodCall(call, receiver, ..) = &expr.kind else {
             return
         };
         // We only care about method calls corresponding to the `Clone`, `Deref` and `Borrow`
@@ -81,7 +81,6 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
         ) {
             return;
         }
-        let receiver = &elements[0];
         let receiver_ty = cx.typeck_results().expr_ty(receiver);
         let expr_ty = cx.typeck_results().expr_ty_adjusted(expr);
         if receiver_ty != expr_ty {

compiler/rustc_lint/src/types.rs

@@ -1458,7 +1458,7 @@ impl InvalidAtomicOrdering {
             sym::AtomicI64,
             sym::AtomicI128,
         ];
-        if let ExprKind::MethodCall(ref method_path, args, _) = &expr.kind
+        if let ExprKind::MethodCall(ref method_path, _, args, _) = &expr.kind
             && recognized_names.contains(&method_path.ident.name)
             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
             && let Some(impl_did) = cx.tcx.impl_of_method(m_def_id)
@@ -1494,8 +1494,8 @@ impl InvalidAtomicOrdering {
     fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
         if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
             && let Some((ordering_arg, invalid_ordering)) = match method {
-                sym::load => Some((&args[1], sym::Release)),
-                sym::store => Some((&args[2], sym::Acquire)),
+                sym::load => Some((&args[0], sym::Release)),
+                sym::store => Some((&args[1], sym::Acquire)),
                 _ => None,
             }
             && let Some(ordering) = Self::match_ordering(cx, ordering_arg)
@@ -1536,8 +1536,8 @@ impl InvalidAtomicOrdering {
             else {return };
 
         let fail_order_arg = match method {
-            sym::fetch_update => &args[2],
-            sym::compare_exchange | sym::compare_exchange_weak => &args[4],
+            sym::fetch_update => &args[1],
+            sym::compare_exchange | sym::compare_exchange_weak => &args[3],
             _ => return,
         };
 

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

@@ -261,15 +261,19 @@ impl<'tcx> Cx<'tcx> {
 
         let kind = match expr.kind {
             // Here comes the interesting stuff:
-            hir::ExprKind::MethodCall(segment, ref args, fn_span) => {
+            hir::ExprKind::MethodCall(segment, receiver, ref args, fn_span) => {
                 // Rewrite a.b(c) into UFCS form like Trait::b(a, c)
                 let expr = self.method_callee(expr, segment.ident.span, None);
                 // 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((args[0].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 = self.mirror_exprs(args);
+                let args = std::iter::once(receiver)
+                    .chain(args.iter())
+                    .map(|expr| self.mirror_expr(expr))
+                    .collect();
                 self.adjustment_span = old_adjustment_span;
                 ExprKind::Call {
                     ty: expr.ty,

compiler/rustc_passes/src/liveness.rs

@@ -1039,9 +1039,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 self.propagate_through_expr(&f, succ)
             }
 
-            hir::ExprKind::MethodCall(.., ref args, _) => {
+            hir::ExprKind::MethodCall(.., receiver, ref args, _) => {
                 let succ = self.check_is_ty_uninhabited(expr, succ);
-                self.propagate_through_exprs(args, succ)
+                let succ = self.propagate_through_exprs(args, succ);
+                self.propagate_through_expr(receiver, succ)
             }
 
             hir::ExprKind::Tup(ref exprs) => self.propagate_through_exprs(exprs, succ),

compiler/rustc_save_analysis/src/dump_visitor.rs

@@ -803,6 +803,7 @@ impl<'tcx> DumpVisitor<'tcx> {
         &mut self,
         ex: &'tcx hir::Expr<'tcx>,
         seg: &'tcx hir::PathSegment<'tcx>,
+        receiver: &'tcx hir::Expr<'tcx>,
         args: &'tcx [hir::Expr<'tcx>],
     ) {
         debug!("process_method_call {:?} {:?}", ex, ex.span);
@@ -823,6 +824,7 @@ impl<'tcx> DumpVisitor<'tcx> {
         }
 
         // walk receiver and args
+        self.visit_expr(receiver);
         walk_list!(self, visit_expr, args);
     }
 
@@ -1340,7 +1342,9 @@ impl<'tcx> Visitor<'tcx> for DumpVisitor<'tcx> {
                 let res = self.save_ctxt.get_path_res(hir_expr.hir_id);
                 self.process_struct_lit(ex, path, fields, adt.variant_of_res(res), *rest)
             }
-            hir::ExprKind::MethodCall(ref seg, args, _) => self.process_method_call(ex, seg, args),
+            hir::ExprKind::MethodCall(ref seg, receiver, args, _) => {
+                self.process_method_call(ex, seg, receiver, args)
+            }
             hir::ExprKind::Field(ref sub_ex, _) => {
                 self.visit_expr(&sub_ex);