Add E0608

Author: GuillaumeGomez

src/librustc_typeck/check/mod.rs

@@ -3889,13 +3889,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                           element_ty
                       }
                       None => {
-                          let mut err = self.type_error_struct(
-                              expr.span,
-                              |actual| {
-                                  format!("cannot index a value of type `{}`",
-                                          actual)
-                              },
-                              base_t);
+                          let mut err = struct_span_err!(tcx.sess, expr.span, E0608,
+                                                         "cannot index into a value of type `{}`",
+                                                         base_t);
                           // Try to give some advice about indexing tuples.
                           if let ty::TyTuple(..) = base_t.sty {
                               let mut needs_note = true;

src/librustc_typeck/diagnostics.rs

@@ -4095,6 +4095,27 @@ assert_eq!(!Question::No, true);
 ```
 "##,
 
+E0608: r##"
+An attempt to index into a type which doesn't implement the `std::ops::Index`
+trait was performed.
+
+Erroneous code example:
+
+```compile_fail,E0608
+0u8[2]; // error: cannot index into a value of type `u8`
+```
+
+To be able to index a value from a type, it needs to implement the
+`std::ops::Index` trait. Example:
+
+```
+let v: Vec<u8> = vec![0, 1, 2, 3];
+
+// The `Vec` type implements the `Index` trait so you can do:
+println!("{}", v[2]);
+```
+"##,
+
 E0609: r##"
 Attempted to access a non-existent field in a struct.
 

src/test/compile-fail/E0608.rs

@@ -0,0 +1,13 @@
+// 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.
+
+fn main() {
+    0u8[2]; //~ ERROR E0608
+}

src/test/compile-fail/index-bot.rs

@@ -9,5 +9,5 @@
 // except according to those terms.
 
 fn main() {
-    (return)[0]; //~ ERROR cannot index a value of type `!`
+    (return)[0]; //~ ERROR cannot index into a value of type `!`
 }

src/test/compile-fail/index_message.rs

@@ -10,5 +10,5 @@
 
 fn main() {
     let z = ();
-    let _ = z[0]; //~ ERROR cannot index a value of type `()`
+    let _ = z[0]; //~ ERROR cannot index into a value of type `()`
 }

src/test/compile-fail/issue-27842.rs

@@ -12,13 +12,13 @@ fn main() {
     let tup = (0, 1, 2);
     // the case where we show a suggestion
     let _ = tup[0];
-    //~^ ERROR cannot index a value of type
+    //~^ ERROR cannot index into a value of type
     //~| HELP to access tuple elements, use
     //~| SUGGESTION let _ = tup.0
 
     // the case where we show just a general hint
     let i = 0_usize;
     let _ = tup[i];
-    //~^ ERROR cannot index a value of type
+    //~^ ERROR cannot index into a value of type
     //~| HELP to access tuple elements, use tuple indexing syntax (e.g. `tuple.0`)
 }

src/test/compile-fail/issue-40861.rs

@@ -12,5 +12,5 @@ fn f(_: &[f32]) {}
 
 fn main() {
     ()[f(&[1.0])];
-    //~^ ERROR cannot index a value of type `()`
+    //~^ ERROR cannot index into a value of type `()`
 }

src/test/compile-fail/slice-2.rs

@@ -14,8 +14,8 @@ struct Foo;
 
 fn main() {
     let x = Foo;
-    &x[..]; //~ ERROR cannot index a value of type `Foo`
-    &x[Foo..]; //~ ERROR cannot index a value of type `Foo`
-    &x[..Foo]; //~ ERROR cannot index a value of type `Foo`
-    &x[Foo..Foo]; //~ ERROR cannot index a value of type `Foo`
+    &x[..]; //~ ERROR cannot index into a value of type `Foo`
+    &x[Foo..]; //~ ERROR cannot index into a value of type `Foo`
+    &x[..Foo]; //~ ERROR cannot index into a value of type `Foo`
+    &x[Foo..Foo]; //~ ERROR cannot index into a value of type `Foo`
 }

src/test/ui/span/suggestion-non-ascii.stderr

@@ -1,4 +1,4 @@
-error: cannot index a value of type `({integer},)`
+error[E0608]: cannot index into a value of type `({integer},)`
   --> $DIR/suggestion-non-ascii.rs:14:21
    |
 14 |     println!("☃{}", tup[0]);