Auto merge of #101261 - TaKO8Ki:separate-receiver-from-arguments-in-hir, r=cjgillot

Separate the receiver from arguments in HIR

Related to #100232

cc `@cjgillot`

Author: bors

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,
                                                                 ..
                                                             },