Rollup merge of #40816 - estebank:issue-38321, r=nikomatsakis

Clarify suggetion for field used as method

Instead of

```rust
error: no method named `src_addr` found for type `&wire::ipv4::Repr` in the current scope
   --> src/wire/ipv4.rs:409:34
    |
409 |         packet.set_src_addr(self.src_addr());
    |                                  ^^^^^^^^
    |
note: did you mean to write `self.src_addr`?
   --> src/wire/ipv4.rs:409:34
    |
409 |         packet.set_src_addr(self.src_addr());
    |                                  ^^^^^^^^
```

present

```rust
error: no method named `src_addr` found for type `&wire::ipv4::Repr` in the current scope
   --> src/wire/ipv4.rs:409:34
    |
409 |         packet.set_src_addr(self.src_addr());
    |                                  ^^^^^^^^ field, not a method
    |
    = help: did you mean to write `self.src_addr` instead of `self.src_addr(...)`?
```

Fix #38321.

src/test/ui/suggestions/confuse-field-and-method/issue-18343.rs

@@ -0,0 +1,21 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Obj<F> where F: FnMut() -> u32 {
+    closure: F,
+}
+
+fn main() {
+    let o = Obj { closure: || 42 };
+    o.closure();
+    //~^ ERROR no method named `closure` found
+    //~| HELP use `(o.closure)(...)` if you meant to call the function stored in the `closure` field
+    //~| NOTE field, not a method
+}

src/test/ui/suggestions/confuse-field-and-method/issue-18343.stderr

@@ -0,0 +1,10 @@
+error: no method named `closure` found for type `Obj<[closure@$DIR/issue-18343.rs:16:28: 16:33]>` in the current scope
+  --> $DIR/issue-18343.rs:17:7
+   |
+17 |     o.closure();
+   |       ^^^^^^^ field, not a method
+   |
+   = help: use `(o.closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: aborting due to previous error
+

src/test/ui/suggestions/confuse-field-and-method/issue-2392.rs

@@ -0,0 +1,105 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(core, fnbox)]
+
+use std::boxed::FnBox;
+
+struct FuncContainer {
+    f1: fn(data: u8),
+    f2: extern "C" fn(data: u8),
+    f3: unsafe fn(data: u8),
+}
+
+struct FuncContainerOuter {
+    container: Box<FuncContainer>
+}
+
+struct Obj<F> where F: FnOnce() -> u32 {
+    closure: F,
+    not_closure: usize,
+}
+
+struct BoxedObj {
+    boxed_closure: Box<FnBox() -> u32>,
+}
+
+struct Wrapper<F> where F: FnMut() -> u32 {
+    wrap: Obj<F>,
+}
+
+fn func() -> u32 {
+    0
+}
+
+fn check_expression() -> Obj<Box<FnBox() -> u32>> {
+    Obj { closure: Box::new(|| 42_u32) as Box<FnBox() -> u32>, not_closure: 42 }
+}
+
+fn main() {
+    // test variations of function
+
+    let o_closure = Obj { closure: || 42, not_closure: 42 };
+    o_closure.closure(); //~ ERROR no method named `closure` found
+    //~^ HELP use `(o_closure.closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+
+    o_closure.not_closure();
+    //~^ ERROR no method named `not_closure` found
+    //~| NOTE field, not a method
+    //~| HELP did you mean to write `o_closure.not_closure` instead of `o_closure.not_closure(...)`?
+
+    let o_func = Obj { closure: func, not_closure: 5 };
+    o_func.closure(); //~ ERROR no method named `closure` found
+    //~^ HELP use `(o_func.closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+
+    let boxed_fn = BoxedObj { boxed_closure: Box::new(func) };
+    boxed_fn.boxed_closure();//~ ERROR no method named `boxed_closure` found
+    //~^ HELP use `(boxed_fn.boxed_closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+
+    let boxed_closure = BoxedObj { boxed_closure: Box::new(|| 42_u32) as Box<FnBox() -> u32> };
+    boxed_closure.boxed_closure();//~ ERROR no method named `boxed_closure` found
+    //~^ HELP use `(boxed_closure.boxed_closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+
+    // test expression writing in the notes
+
+    let w = Wrapper { wrap: o_func };
+    w.wrap.closure();//~ ERROR no method named `closure` found
+    //~^ HELP use `(w.wrap.closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+
+    w.wrap.not_closure();
+    //~^ ERROR no method named `not_closure` found
+    //~| NOTE field, not a method
+    //~| HELP did you mean to write `w.wrap.not_closure` instead of `w.wrap.not_closure(...)`?
+
+    check_expression().closure();//~ ERROR no method named `closure` found
+    //~^ HELP use `(check_expression().closure)(...)` if you meant to call the function stored
+    //~| NOTE field, not a method
+}
+
+impl FuncContainerOuter {
+    fn run(&self) {
+        unsafe {
+            (*self.container).f1(1); //~ ERROR no method named `f1` found
+            //~^ HELP use `((*self.container).f1)(...)`
+            //~| NOTE field, not a method
+            (*self.container).f2(1); //~ ERROR no method named `f2` found
+            //~^ HELP use `((*self.container).f2)(...)`
+            //~| NOTE field, not a method
+            (*self.container).f3(1); //~ ERROR no method named `f3` found
+            //~^ HELP use `((*self.container).f3)(...)`
+            //~| NOTE field, not a method
+        }
+    }
+}

src/test/ui/suggestions/confuse-field-and-method/issue-2392.stderr

@@ -0,0 +1,90 @@
+error: no method named `closure` found for type `Obj<[closure@$DIR/issue-2392.rs:49:36: 49:41]>` in the current scope
+  --> $DIR/issue-2392.rs:50:15
+   |
+50 |     o_closure.closure(); //~ ERROR no method named `closure` found
+   |               ^^^^^^^ field, not a method
+   |
+   = help: use `(o_closure.closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: no method named `not_closure` found for type `Obj<[closure@$DIR/issue-2392.rs:49:36: 49:41]>` in the current scope
+  --> $DIR/issue-2392.rs:54:15
+   |
+54 |     o_closure.not_closure();
+   |               ^^^^^^^^^^^ field, not a method
+   |
+   = help: did you mean to write `o_closure.not_closure` instead of `o_closure.not_closure(...)`?
+
+error: no method named `closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
+  --> $DIR/issue-2392.rs:60:12
+   |
+60 |     o_func.closure(); //~ ERROR no method named `closure` found
+   |            ^^^^^^^ field, not a method
+   |
+   = help: use `(o_func.closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: no method named `boxed_closure` found for type `BoxedObj` in the current scope
+  --> $DIR/issue-2392.rs:65:14
+   |
+65 |     boxed_fn.boxed_closure();//~ ERROR no method named `boxed_closure` found
+   |              ^^^^^^^^^^^^^ field, not a method
+   |
+   = help: use `(boxed_fn.boxed_closure)(...)` if you meant to call the function stored in the `boxed_closure` field
+
+error: no method named `boxed_closure` found for type `BoxedObj` in the current scope
+  --> $DIR/issue-2392.rs:70:19
+   |
+70 |     boxed_closure.boxed_closure();//~ ERROR no method named `boxed_closure` found
+   |                   ^^^^^^^^^^^^^ field, not a method
+   |
+   = help: use `(boxed_closure.boxed_closure)(...)` if you meant to call the function stored in the `boxed_closure` field
+
+error: no method named `closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
+  --> $DIR/issue-2392.rs:77:12
+   |
+77 |     w.wrap.closure();//~ ERROR no method named `closure` found
+   |            ^^^^^^^ field, not a method
+   |
+   = help: use `(w.wrap.closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: no method named `not_closure` found for type `Obj<fn() -> u32 {func}>` in the current scope
+  --> $DIR/issue-2392.rs:81:12
+   |
+81 |     w.wrap.not_closure();
+   |            ^^^^^^^^^^^ field, not a method
+   |
+   = help: did you mean to write `w.wrap.not_closure` instead of `w.wrap.not_closure(...)`?
+
+error: no method named `closure` found for type `Obj<std::boxed::Box<std::boxed::FnBox<(), Output=u32> + 'static>>` in the current scope
+  --> $DIR/issue-2392.rs:86:24
+   |
+86 |     check_expression().closure();//~ ERROR no method named `closure` found
+   |                        ^^^^^^^ field, not a method
+   |
+   = help: use `(check_expression().closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: no method named `f1` found for type `FuncContainer` in the current scope
+  --> $DIR/issue-2392.rs:94:31
+   |
+94 |             (*self.container).f1(1); //~ ERROR no method named `f1` found
+   |                               ^^ field, not a method
+   |
+   = help: use `((*self.container).f1)(...)` if you meant to call the function stored in the `f1` field
+
+error: no method named `f2` found for type `FuncContainer` in the current scope
+  --> $DIR/issue-2392.rs:97:31
+   |
+97 |             (*self.container).f2(1); //~ ERROR no method named `f2` found
+   |                               ^^ field, not a method
+   |
+   = help: use `((*self.container).f2)(...)` if you meant to call the function stored in the `f2` field
+
+error: no method named `f3` found for type `FuncContainer` in the current scope
+   --> $DIR/issue-2392.rs:100:31
+    |
+100 |             (*self.container).f3(1); //~ ERROR no method named `f3` found
+    |                               ^^ field, not a method
+    |
+    = help: use `((*self.container).f3)(...)` if you meant to call the function stored in the `f3` field
+
+error: aborting due to 11 previous errors
+

src/test/ui/suggestions/confuse-field-and-method/issue-32128.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Example {
+    example: Box<Fn(i32) -> i32>
+}
+
+fn main() {
+    let demo = Example {
+        example: Box::new(|x| {
+            x + 1
+        })
+    };
+
+    demo.example(1);
+    //~^ ERROR no method named `example`
+    //~| HELP use `(demo.example)(...)`
+    //~| NOTE field, not a method
+    // (demo.example)(1);
+}

src/test/ui/suggestions/confuse-field-and-method/issue-32128.stderr

@@ -0,0 +1,10 @@
+error: no method named `example` found for type `Example` in the current scope
+  --> $DIR/issue-32128.rs:22:10
+   |
+22 |     demo.example(1);
+   |          ^^^^^^^ field, not a method
+   |
+   = help: use `(demo.example)(...)` if you meant to call the function stored in the `example` field
+
+error: aborting due to previous error
+

src/test/ui/suggestions/confuse-field-and-method/issue-33784.rs

@@ -0,0 +1,49 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::ops::Deref;
+
+struct Obj<F> where F: FnMut() -> u32 {
+    fn_ptr: fn() -> (),
+    closure: F,
+}
+
+struct C {
+    c_fn_ptr: fn() -> (),
+}
+
+struct D(C);
+
+impl Deref for D {
+    type Target = C;
+    fn deref(&self) -> &C {
+        &self.0
+    }
+}
+
+
+fn empty() {}
+
+fn main() {
+    let o = Obj { fn_ptr: empty, closure: || 42 };
+    let p = &o;
+    p.closure(); //~ ERROR no method named `closure` found
+    //~^ HELP use `(p.closure)(...)` if you meant to call the function stored in the `closure` field
+    //~| NOTE `closure` is a field storing a function, not a method
+    let q = &p;
+    q.fn_ptr(); //~ ERROR no method named `fn_ptr` found
+    //~^ HELP use `(q.fn_ptr)(...)` if you meant to call the function stored in the `fn_ptr` field
+    //~| NOTE `fn_ptr` is a field storing a function, not a method
+    let r = D(C { c_fn_ptr: empty });
+    let s = &r;
+    s.c_fn_ptr(); //~ ERROR no method named `c_fn_ptr` found
+    //~^ HELP use `(s.c_fn_ptr)(...)` if you meant to call the function stored in the `c_fn_ptr`
+    //~| NOTE `c_fn_ptr` is a field storing a function, not a method
+}

src/test/ui/suggestions/confuse-field-and-method/issue-33784.stderr

@@ -0,0 +1,26 @@
+error: no method named `closure` found for type `&Obj<[closure@$DIR/issue-33784.rs:35:43: 35:48]>` in the current scope
+  --> $DIR/issue-33784.rs:37:7
+   |
+37 |     p.closure(); //~ ERROR no method named `closure` found
+   |       ^^^^^^^ field, not a method
+   |
+   = help: use `(p.closure)(...)` if you meant to call the function stored in the `closure` field
+
+error: no method named `fn_ptr` found for type `&&Obj<[closure@$DIR/issue-33784.rs:35:43: 35:48]>` in the current scope
+  --> $DIR/issue-33784.rs:41:7
+   |
+41 |     q.fn_ptr(); //~ ERROR no method named `fn_ptr` found
+   |       ^^^^^^ field, not a method
+   |
+   = help: use `(q.fn_ptr)(...)` if you meant to call the function stored in the `fn_ptr` field
+
+error: no method named `c_fn_ptr` found for type `&D` in the current scope
+  --> $DIR/issue-33784.rs:46:7
+   |
+46 |     s.c_fn_ptr(); //~ ERROR no method named `c_fn_ptr` found
+   |       ^^^^^^^^ field, not a method
+   |
+   = help: use `(s.c_fn_ptr)(...)` if you meant to call the function stored in the `c_fn_ptr` field
+
+error: aborting due to 3 previous errors
+