Add E0611

Author: GuillaumeGomez

src/librustc_typeck/check/mod.rs

@@ -3051,8 +3051,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         if let Some((did, field_ty)) = private_candidate {
             let struct_path = self.tcx().item_path_str(did);
-            let msg = format!("field `{}` of struct `{}` is private", idx.node, struct_path);
-            self.tcx().sess.span_err(expr.span, &msg);
+            struct_span_err!(self.tcx().sess, expr.span, E0611,
+                             "field `{}` of tuple-struct `{}` is private",
+                             idx.node, struct_path);
             return field_ty;
         }
 

src/librustc_typeck/diagnostics.rs

@@ -4152,6 +4152,62 @@ println!("x: {}, y: {}", variable.x, variable.y);
 For more information see The Rust Book: https://doc.rust-lang.org/book/
 "##,
 
+E0611: r##"
+Attempted to access a private field on a tuple-struct.
+
+Erroneous code example:
+
+```compile_fail,E0611
+mod some_module {
+    pub struct Foo(u32);
+
+    impl Foo {
+        pub fn new() -> Foo { Foo(0) }
+    }
+}
+
+let y = some_module::Foo::new();
+println!("{}", y.0); // error: field `0` of tuple-struct `some_module::Foo`
+                     //        is private
+```
+
+Since the field is private, you have two solutions:
+
+1) Make the field public:
+
+```
+mod some_module {
+    pub struct Foo(pub u32); // The field is now public.
+
+    impl Foo {
+        pub fn new() -> Foo { Foo(0) }
+    }
+}
+
+let y = some_module::Foo::new();
+println!("{}", y.0); // So we can access it directly.
+```
+
+2) Add a getter function to keep the field private but allow for accessing its
+value:
+
+```
+mod some_module {
+    pub struct Foo(u32);
+
+    impl Foo {
+        pub fn new() -> Foo { Foo(0) }
+
+        // We add the getter function.
+        pub fn get(&self) -> &u32 { self.0 }
+    }
+}
+
+let y = some_module::Foo::new();
+println!("{}", y.get()); // So we can get the value through the function.
+```
+"##,
+
 E0617: r##"
 Attempted to pass an invalid type of variable into a variadic function.
 

src/test/compile-fail/E0611.rs

@@ -0,0 +1,22 @@
+// 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.
+
+mod a {
+    pub struct Foo(u32);
+
+    impl Foo {
+        pub fn new() -> Foo { Foo(0) }
+    }
+}
+
+fn main() {
+   let y = a::Foo::new();
+   y.0; //~ ERROR E0611
+}