Do not consider method call receiver as an argument in AST.

compiler/rustc_ast/src/ast.rs

@@ -1338,14 +1338,13 @@ pub enum ExprKind {
     ///
     /// The `PathSegment` represents the method name and its generic arguments
     /// (within the angle brackets).
-    /// The first element of the vector of an `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.
-    /// Thus, `x.foo::<Bar, Baz>(a, b, c, d)` is represented as
-    /// `ExprKind::MethodCall(PathSegment { foo, [Bar, Baz] }, [x, a, b, c, d])`.
+    /// The standalone `Expr` is the receiver expression.
+    /// The vector of `Expr` is the arguments.
+    /// `x.foo::<Bar, Baz>(a, b, c, d)` is represented as
+    /// `ExprKind::MethodCall(PathSegment { foo, [Bar, Baz] }, x, [a, b, c, d])`.
     /// This `Span` is the span of the function, without the dot and receiver
     /// (e.g. `foo(a, b)` in `x.foo(a, b)`
-    MethodCall(PathSegment, Vec<P<Expr>>, Span),
+    MethodCall(PathSegment, P<Expr>, Vec<P<Expr>>, Span),
     /// A tuple (e.g., `(a, b, c, d)`).
     Tup(Vec<P<Expr>>),
     /// A binary operation (e.g., `a + b`, `a * b`).

compiler/rustc_ast/src/mut_visit.rs

@@ -1302,10 +1302,11 @@ pub fn noop_visit_expr<T: MutVisitor>(
             vis.visit_expr(f);
             visit_exprs(args, vis);
         }
-        ExprKind::MethodCall(PathSegment { ident, id, args }, exprs, span) => {
+        ExprKind::MethodCall(PathSegment { ident, id, args }, receiver, exprs, span) => {
             vis.visit_ident(ident);
             vis.visit_id(id);
             visit_opt(args, |args| vis.visit_generic_args(args));
+            vis.visit_expr(receiver);
             visit_exprs(exprs, vis);
             vis.visit_span(span);
         }

compiler/rustc_ast/src/util/parser.rs

@@ -396,9 +396,9 @@ pub fn contains_exterior_struct_lit(value: &ast::Expr) -> bool {
             contains_exterior_struct_lit(&x)
         }
 
-        ast::ExprKind::MethodCall(.., ref exprs, _) => {
+        ast::ExprKind::MethodCall(_, ref receiver, _, _) => {
             // X { y: 1 }.bar(...)
-            contains_exterior_struct_lit(&exprs[0])
+            contains_exterior_struct_lit(&receiver)
         }
 
         _ => false,

compiler/rustc_ast/src/visit.rs

@@ -813,8 +813,9 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_expr(callee_expression);
             walk_list!(visitor, visit_expr, arguments);
         }
-        ExprKind::MethodCall(ref segment, ref arguments, _span) => {
+        ExprKind::MethodCall(ref segment, ref receiver, ref arguments, _span) => {
             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_ast_lowering/src/expr.rs

@@ -62,7 +62,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         hir::ExprKind::Call(f, self.lower_exprs(args))
                     }
                 }
-                ExprKind::MethodCall(ref seg, ref args, span) => {
+                ExprKind::MethodCall(ref seg, ref receiver, ref args, span) => {
                     let hir_seg = self.arena.alloc(self.lower_path_segment(
                         e.span,
                         seg,
@@ -70,7 +70,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         ParenthesizedGenericArgs::Err,
                         ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                     ));
-                    let args = self.lower_exprs(args);
+                    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))
                 }
                 ExprKind::Binary(binop, ref lhs, ref rhs) => {

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -193,9 +193,13 @@ impl<'a> State<'a> {
         self.print_call_post(args)
     }
 
-    fn print_expr_method_call(&mut self, segment: &ast::PathSegment, args: &[P<ast::Expr>]) {
-        let base_args = &args[1..];
-        self.print_expr_maybe_paren(&args[0], parser::PREC_POSTFIX);
+    fn print_expr_method_call(
+        &mut self,
+        segment: &ast::PathSegment,
+        receiver: &ast::Expr,
+        base_args: &[P<ast::Expr>],
+    ) {
+        self.print_expr_maybe_paren(receiver, parser::PREC_POSTFIX);
         self.word(".");
         self.print_ident(segment.ident);
         if let Some(ref args) = segment.args {
@@ -303,8 +307,8 @@ impl<'a> State<'a> {
             ast::ExprKind::Call(ref func, ref args) => {
                 self.print_expr_call(func, &args);
             }
-            ast::ExprKind::MethodCall(ref segment, ref args, _) => {
-                self.print_expr_method_call(segment, &args);
+            ast::ExprKind::MethodCall(ref segment, ref receiver, ref args, _) => {
+                self.print_expr_method_call(segment, &receiver, &args);
             }
             ast::ExprKind::Binary(op, ref lhs, ref rhs) => {
                 self.print_expr_binary(op, lhs, rhs);

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -240,8 +240,8 @@ impl<'cx, 'a> Context<'cx, 'a> {
                 self.manage_cond_expr(prefix);
                 self.manage_cond_expr(suffix);
             }
-            ExprKind::MethodCall(_, ref mut local_exprs, _) => {
-                for local_expr in local_exprs.iter_mut().skip(1) {
+            ExprKind::MethodCall(_, _,ref mut local_exprs, _) => {
+                for local_expr in local_exprs.iter_mut() {
                     self.manage_cond_expr(local_expr);
                 }
             }
@@ -377,14 +377,12 @@ impl<'cx, 'a> Context<'cx, 'a> {
                     id: DUMMY_NODE_ID,
                     ident: Ident::new(sym::try_capture, self.span),
                 },
-                vec![
                 expr_paren(self.cx, self.span, self.cx.expr_addr_of(self.span, wrapper)),
-                    expr_addr_of_mut(
+                vec![expr_addr_of_mut(
                     self.cx,
                     self.span,
                     self.cx.expr_path(Path::from_ident(capture)),
-                    ),
-                ],
+                )],
                 self.span,
             ))
             .add_trailing_semicolon();
@@ -442,10 +440,11 @@ fn expr_addr_of_mut(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {
 fn expr_method_call(
     cx: &ExtCtxt<'_>,
     path: PathSegment,
+    receiver: P<Expr>,
     args: Vec<P<Expr>>,
     span: Span,
 ) -> P<Expr> {
-    cx.expr(span, ExprKind::MethodCall(path, args, span))
+    cx.expr(span, ExprKind::MethodCall(path, receiver, args, span))
 }
 
 fn expr_paren(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {

compiler/rustc_lint/src/unused.rs

@@ -608,8 +608,7 @@ trait UnusedDelimLint {
             ref call_or_other => {
                 let (args_to_check, ctx) = match *call_or_other {
                     Call(_, ref args) => (&args[..], UnusedDelimsCtx::FunctionArg),
-                    // first "argument" is self (which sometimes needs delims)
-                    MethodCall(_, ref args, _) => (&args[1..], UnusedDelimsCtx::MethodArg),
+                    MethodCall(_, _, ref args, _) => (&args[..], UnusedDelimsCtx::MethodArg),
                     // actual catch-all arm
                     _ => {
                         return;

compiler/rustc_parse/src/parser/expr.rs

@@ -850,7 +850,7 @@ impl<'a> Parser<'a> {
                     ExprKind::Index(_, _) => "indexing",
                     ExprKind::Try(_) => "`?`",
                     ExprKind::Field(_, _) => "a field access",
-                    ExprKind::MethodCall(_, _, _) => "a method call",
+                    ExprKind::MethodCall(_, _, _, _) => "a method call",
                     ExprKind::Call(_, _) => "a function call",
                     ExprKind::Await(_) => "`.await`",
                     ExprKind::Err => return Ok(with_postfix),
@@ -1280,12 +1280,14 @@ impl<'a> Parser<'a> {
 
         if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
             // Method call `expr.f()`
-            let mut args = self.parse_paren_expr_seq()?;
-            args.insert(0, self_arg);
-
+            let args = self.parse_paren_expr_seq()?;
             let fn_span = fn_span_lo.to(self.prev_token.span);
             let span = lo.to(self.prev_token.span);
-            Ok(self.mk_expr(span, ExprKind::MethodCall(segment, args, fn_span), AttrVec::new()))
+            Ok(self.mk_expr(
+                span,
+                ExprKind::MethodCall(segment, self_arg, args, fn_span),
+                AttrVec::new(),
+            ))
         } else {
             // Field access `expr.f`
             if let Some(args) = segment.args {

compiler/rustc_resolve/src/late.rs

@@ -3796,9 +3796,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             ExprKind::Field(ref subexpression, _) => {
                 self.resolve_expr(subexpression, Some(expr));
             }
-            ExprKind::MethodCall(ref segment, ref arguments, _) => {
-                let mut arguments = arguments.iter();
-                self.resolve_expr(arguments.next().unwrap(), Some(expr));
+            ExprKind::MethodCall(ref segment, ref receiver, ref arguments, _) => {
+                self.resolve_expr(receiver, Some(expr));
                 for argument in arguments {
                     self.resolve_expr(argument, None);
                 }

src/test/ui/cfg/cfg-method-receiver.rs

@@ -0,0 +1,12 @@
+macro_rules! cbor_map {
+    ($key:expr) => {
+        $key.signum();
+        //~^ ERROR can't call method `signum` on ambiguous numeric type `{integer}` [E0689]
+    };
+}
+
+fn main() {
+    cbor_map! { #[cfg(test)] 4};
+    //~^ ERROR attributes on expressions are experimental
+    //~| ERROR removing an expression is not supported in this position
+}

src/test/ui/cfg/cfg-method-receiver.stderr

@@ -0,0 +1,34 @@
+error[E0658]: attributes on expressions are experimental
+  --> $DIR/cfg-method-receiver.rs:9:17
+   |
+LL |     cbor_map! { #[cfg(test)] 4};
+   |                 ^^^^^^^^^^^^
+   |
+   = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
+   = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable
+
+error: removing an expression is not supported in this position
+  --> $DIR/cfg-method-receiver.rs:9:17
+   |
+LL |     cbor_map! { #[cfg(test)] 4};
+   |                 ^^^^^^^^^^^^
+
+error[E0689]: can't call method `signum` on ambiguous numeric type `{integer}`
+  --> $DIR/cfg-method-receiver.rs:3:14
+   |
+LL |         $key.signum();
+   |              ^^^^^^
+...
+LL |     cbor_map! { #[cfg(test)] 4};
+   |     --------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `cbor_map` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: you must specify a concrete type for this numeric value, like `i32`
+   |
+LL |     cbor_map! { #[cfg(test)] 4_i32};
+   |                              ~~~~~
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0658, E0689.
+For more information about an error, try `rustc --explain E0658`.

src/tools/clippy/clippy_lints/src/double_parens.rs

@@ -61,9 +61,8 @@ impl EarlyLintPass for DoubleParens {
                     }
                 }
             },
-            ExprKind::MethodCall(_, ref params, _) => {
-                if params.len() == 2 {
-                    let param = &params[1];
+            ExprKind::MethodCall(_, _, ref params, _) => {
+                if let [ref param] = params[..] {
                     if let ExprKind::Paren(_) = param.kind {
                         span_lint(cx, DOUBLE_PARENS, param.span, msg);
                     }

src/tools/clippy/clippy_lints/src/option_env_unwrap.rs

@@ -37,9 +37,9 @@ declare_lint_pass!(OptionEnvUnwrap => [OPTION_ENV_UNWRAP]);
 impl EarlyLintPass for OptionEnvUnwrap {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
         if_chain! {
-            if let ExprKind::MethodCall(path_segment, args, _) = &expr.kind;
+            if let ExprKind::MethodCall(path_segment, receiver, _, _) = &expr.kind;
             if matches!(path_segment.ident.name, sym::expect | sym::unwrap);
-            if let ExprKind::Call(caller, _) = &args[0].kind;
+            if let ExprKind::Call(caller, _) = &receiver.kind;
             if is_direct_expn_of(caller.span, "option_env").is_some();
             then {
                 span_lint_and_help(

src/tools/clippy/clippy_lints/src/precedence.rs

@@ -109,12 +109,12 @@ impl EarlyLintPass for Precedence {
             let mut arg = operand;
 
             let mut all_odd = true;
-            while let ExprKind::MethodCall(path_segment, args, _) = &arg.kind {
+            while let ExprKind::MethodCall(path_segment, receiver, _, _) = &arg.kind {
                 let path_segment_str = path_segment.ident.name.as_str();
                 all_odd &= ALLOWED_ODD_FUNCTIONS
                     .iter()
                     .any(|odd_function| **odd_function == *path_segment_str);
-                arg = args.first().expect("A method always has a receiver.");
+                arg = receiver;
             }
 
             if_chain! {

src/tools/clippy/clippy_lints/src/suspicious_operation_groupings.rs

@@ -595,7 +595,7 @@ fn ident_difference_expr_with_base_location(
         | (Unary(_, _), Unary(_, _))
         | (Binary(_, _, _), Binary(_, _, _))
         | (Tup(_), Tup(_))
-        | (MethodCall(_, _, _), MethodCall(_, _, _))
+        | (MethodCall(_, _, _, _), MethodCall(_, _, _, _))
         | (Call(_, _), Call(_, _))
         | (ConstBlock(_), ConstBlock(_))
         | (Array(_), Array(_))

src/tools/clippy/clippy_lints/src/unused_rounding.rs

@@ -30,11 +30,10 @@ declare_clippy_lint! {
 declare_lint_pass!(UnusedRounding => [UNUSED_ROUNDING]);
 
 fn is_useless_rounding(expr: &Expr) -> Option<(&str, String)> {
-    if let ExprKind::MethodCall(name_ident, args, _) = &expr.kind
+    if let ExprKind::MethodCall(name_ident, receiver, _, _) = &expr.kind
         && let method_name = name_ident.ident.name.as_str()
         && (method_name == "ceil" || method_name == "round" || method_name == "floor")
-        && !args.is_empty()
-        && let ExprKind::Lit(spanned) = &args[0].kind
+        && let ExprKind::Lit(spanned) = &receiver.kind
         && let LitKind::Float(symbol, ty) = spanned.kind {
             let f = symbol.as_str().parse::<f64>().unwrap();
             let f_str = symbol.to_string() + if let LitFloatType::Suffixed(ty) = ty {

src/tools/clippy/clippy_utils/src/ast_utils.rs

@@ -147,7 +147,9 @@ pub fn eq_expr(l: &Expr, r: &Expr) -> bool {
         (Array(l), Array(r)) | (Tup(l), Tup(r)) => over(l, r, |l, r| eq_expr(l, r)),
         (Repeat(le, ls), Repeat(re, rs)) => eq_expr(le, re) && eq_expr(&ls.value, &rs.value),
         (Call(lc, la), Call(rc, ra)) => eq_expr(lc, rc) && over(la, ra, |l, r| eq_expr(l, r)),
-        (MethodCall(lc, la, _), MethodCall(rc, ra, _)) => eq_path_seg(lc, rc) && over(la, ra, |l, r| eq_expr(l, r)),
+        (MethodCall(lc, ls, la, _), MethodCall(rc, rs, ra, _)) => {
+            eq_path_seg(lc, rc) && eq_expr(ls, rs) && over(la, ra, |l, r| eq_expr(l, r))
+        },
         (Binary(lo, ll, lr), Binary(ro, rl, rr)) => lo.node == ro.node && eq_expr(ll, rl) && eq_expr(lr, rr),
         (Unary(lo, l), Unary(ro, r)) => mem::discriminant(lo) == mem::discriminant(ro) && eq_expr(l, r),
         (Lit(l), Lit(r)) => l.kind == r.kind,

src/tools/rustfmt/src/chains.rs

@@ -145,7 +145,7 @@ impl ChainItemKind {
 
     fn from_ast(context: &RewriteContext<'_>, expr: &ast::Expr) -> (ChainItemKind, Span) {
         let (kind, span) = match expr.kind {
-            ast::ExprKind::MethodCall(ref segment, ref expressions, _) => {
+            ast::ExprKind::MethodCall(ref segment, ref receiver, ref expressions, _) => {
                 let types = if let Some(ref generic_args) = segment.args {
                     if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
                         data.args
@@ -163,7 +163,7 @@ impl ChainItemKind {
                 } else {
                     vec![]
                 };
-                let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
+                let span = mk_sp(receiver.span.hi(), expr.span.hi());
                 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
                 (kind, span)
             }
@@ -253,7 +253,7 @@ impl ChainItem {
             format!("::<{}>", type_list.join(", "))
         };
         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
-        rewrite_call(context, &callee_str, &args[1..], span, shape)
+        rewrite_call(context, &callee_str, &args, span, shape)
     }
 }
 
@@ -400,8 +400,8 @@ impl Chain {
     // is a try! macro, we'll convert it to shorthand when the option is set.
     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
         match expr.kind {
-            ast::ExprKind::MethodCall(_, ref expressions, _) => {
-                Some(Self::convert_try(&expressions[0], context))
+            ast::ExprKind::MethodCall(_, ref receiver, _, _) => {
+                Some(Self::convert_try(&receiver, context))
             }
             ast::ExprKind::Field(ref subexpr, _)
             | ast::ExprKind::Try(ref subexpr)