Rollup merge of #41062 - estebank:private-field, r=arielb1

Do not recommend private fields called as method

```rust
error: no method named `dog_age` found for type `animal::Dog` in the current scope
  --> $DIR/private-field.rs:26:23
   |
26 |     let dog_age = dog.dog_age();
   |                       ^^^^^^^ private field, not a method
```
Fix #27654.

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

@@ -0,0 +1,29 @@
+// Copyright 2017 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.
+
+pub mod animal {
+    pub struct Dog {
+        pub age: usize,
+        dog_age: usize,
+    }
+
+    impl Dog {
+        pub fn new(age: usize) -> Dog {
+            Dog { age: age, dog_age: age * 7 }
+        }
+    }
+}
+
+fn main() {
+    let dog = animal::Dog::new(3);
+    let dog_age = dog.dog_age();
+    //let dog_age = dog.dog_age;
+    println!("{}", dog_age);
+}

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

@@ -0,0 +1,8 @@
+error: no method named `dog_age` found for type `animal::Dog` in the current scope
+  --> $DIR/private-field.rs:26:23
+   |
+26 |     let dog_age = dog.dog_age();
+   |                       ^^^^^^^ private field, not a method
+
+error: aborting due to previous error
+