Refer to types using the local identifier

On type errors, refer to types using the locally available name when
they have been imported into scope instead of the fully qualified path.

```
error[E0308]: mismatched types
 --> file.rs:7:24
  |
7 |     let y: Option<X> = Ok(());
  |                        ^^^^^^ expected enum `std::option::Option`, found enum `std::result::Result`
  |
  = note: expected type `Option<X>`
             found type `Result<(), _>`
  = help: here are some functions which might fulfill your needs:
          - .err()
          - .unwrap_err()
```

src/librustc/middle/const_val.rs

@@ -76,6 +76,10 @@ impl<'tcx> ConstVal<'tcx> {
             _ => None
         }
     }
+
+    pub fn to_usize(&self) -> Option<usize> {
+        self.to_const_int().and_then(|i| i.to_usize())
+    }
 }
 
 #[derive(Clone, Debug)]

src/librustc/ty/context.rs

@@ -1179,6 +1179,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.all_crate_nums(LOCAL_CRATE)
     }
 
+    pub fn cstore(&self) -> &CrateStore {
+        self.cstore
+    }
+
     pub fn def_key(self, id: DefId) -> hir_map::DefKey {
         if id.is_local() {
             self.hir.def_key(id)

src/librustc/ty/sty.rs

@@ -1469,4 +1469,10 @@ pub struct Const<'tcx> {
     pub val: ConstVal<'tcx>,
 }
 
+impl<'tcx> Const<'tcx> {
+    pub fn usize_val(&self) -> usize {
+        self.val.to_usize().unwrap_or(0)
+    }
+}
+
 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Const<'tcx> {}

src/librustc_const_math/int.rs

@@ -188,6 +188,15 @@ impl ConstInt {
         })
     }
 
+    /// Converts the value to a `usize` if it's in the range 0...std::usize::MAX
+    pub fn to_usize(&self) -> Option<usize> {
+        self.to_u128().and_then(|v| if v <= usize::max_value() as u128 {
+            Some(v as usize)
+        } else {
+            None
+        })
+    }
+
     /// Converts the value to a `u128` if it's in the range 0...std::u128::MAX
     pub fn to_u128(&self) -> Option<u128> {
         match *self {

src/test/compile-fail/bad-const-type.rs

@@ -10,7 +10,7 @@
 
 static i: String = 10;
 //~^ ERROR mismatched types
-//~| expected type `std::string::String`
+//~| expected type `String`
 //~| found type `{integer}`
 //~| expected struct `std::string::String`, found integral variable
 fn main() { println!("{}", i); }

src/test/compile-fail/cross-borrow-trait.rs

@@ -19,5 +19,5 @@ pub fn main() {
     let x: Box<Trait> = Box::new(Foo);
     let _y: &Trait = x; //~ ERROR E0308
                         //~| expected type `&Trait`
-                        //~| found type `std::boxed::Box<Trait>`
+                        //~| found type `Box<Trait>`
 }

src/test/compile-fail/destructure-trait-ref.rs

@@ -51,5 +51,5 @@ fn main() {
     let box box x = box 1isize as Box<T>;
     //~^ ERROR mismatched types
     //~| expected type `T`
-    //~| found type `std::boxed::Box<_>`
+    //~| found type `Box<_>`
 }

src/test/compile-fail/fn-trait-formatting.rs

@@ -16,15 +16,15 @@ fn main() {
     let _: () = (box |_: isize| {}) as Box<FnOnce(isize)>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::FnOnce(isize)>`
+    //~| found type `Box<std::ops::FnOnce(isize)>`
     let _: () = (box |_: isize, isize| {}) as Box<Fn(isize, isize)>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::Fn(isize, isize)>`
+    //~| found type `Box<std::ops::Fn(isize, isize)>`
     let _: () = (box || -> isize { unimplemented!() }) as Box<FnMut() -> isize>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::FnMut() -> isize>`
+    //~| found type `Box<std::ops::FnMut() -> isize>`
 
     needs_fn(1);
     //~^ ERROR : std::ops::Fn<(isize,)>`

src/test/compile-fail/fully-qualified-type-name1.rs

@@ -14,7 +14,7 @@ fn main() {
     let x: Option<usize>;
     x = 5;
     //~^ ERROR mismatched types
-    //~| expected type `std::option::Option<usize>`
+    //~| expected type `Option<usize>`
     //~| found type `{integer}`
     //~| expected enum `std::option::Option`, found integral variable
 }

src/test/compile-fail/fully-qualified-type-name4.rs

@@ -15,7 +15,7 @@ use std::option::Option;
 fn bar(x: usize) -> Option<usize> {
     return x;
     //~^ ERROR mismatched types
-    //~| expected type `std::option::Option<usize>`
+    //~| expected type `Option<usize>`
     //~| found type `usize`
     //~| expected enum `std::option::Option`, found usize
 }

src/test/compile-fail/generic-type-params-name-repr.rs

@@ -36,12 +36,12 @@ fn main() {
     // Including cases where the default is using previous type params.
     let _: HashMap<String, isize> = ();
     //~^ ERROR mismatched types
-    //~| expected type `HashMap<std::string::String, isize>`
+    //~| expected type `HashMap<String, isize>`
     //~| found type `()`
     //~| expected struct `HashMap`, found ()
     let _: HashMap<String, isize, Hash<String>> = ();
     //~^ ERROR mismatched types
-    //~| expected type `HashMap<std::string::String, isize>`
+    //~| expected type `HashMap<String, isize>`
     //~| found type `()`
     //~| expected struct `HashMap`, found ()
 

src/test/compile-fail/issue-13466.rs

@@ -17,14 +17,14 @@ pub fn main() {
     let _x: usize = match Some(1) {
         Ok(u) => u,
         //~^ ERROR mismatched types
-        //~| expected type `std::option::Option<{integer}>`
-        //~| found type `std::result::Result<_, _>`
+        //~| expected type `Option<{integer}>`
+        //~| found type `Result<_, _>`
         //~| expected enum `std::option::Option`, found enum `std::result::Result`
 
         Err(e) => panic!(e)
         //~^ ERROR mismatched types
-        //~| expected type `std::option::Option<{integer}>`
-        //~| found type `std::result::Result<_, _>`
+        //~| expected type `Option<{integer}>`
+        //~| found type `Result<_, _>`
         //~| expected enum `std::option::Option`, found enum `std::result::Result`
     };
 }

src/test/compile-fail/issue-15783.rs

@@ -17,8 +17,8 @@ fn main() {
     let x = Some(&[name]);
     let msg = foo(x);
 //~^ ERROR mismatched types
-//~| expected type `std::option::Option<&[&str]>`
-//~| found type `std::option::Option<&[&str; 1]>`
+//~| expected type `Option<&[&str]>`
+//~| found type `Option<&[&str; 1]>`
 //~| expected slice, found array of 1 elements
     assert_eq!(msg, 3);
 }

src/test/compile-fail/issue-3680.rs

@@ -12,8 +12,8 @@ fn main() {
     match None {
         Err(_) => ()
         //~^ ERROR mismatched types
-        //~| expected type `std::option::Option<_>`
-        //~| found type `std::result::Result<_, _>`
+        //~| expected type `Option<_>`
+        //~| found type `Result<_, _>`
         //~| expected enum `std::option::Option`, found enum `std::result::Result`
     }
 }

src/test/compile-fail/issue-40749.rs

@@ -12,5 +12,5 @@ fn main() {
     [0; ..10];
     //~^ ERROR mismatched types
     //~| expected type `usize`
-    //~| found type `std::ops::RangeTo<{integer}>`
+    //~| found type `RangeTo<{integer}>`
 }

src/test/compile-fail/issue-5100.rs

@@ -43,7 +43,7 @@ fn main() {
         box (true, false) => ()
 //~^ ERROR mismatched types
 //~| expected type `(bool, bool)`
-//~| found type `std::boxed::Box<_>`
+//~| found type `Box<_>`
     }
 
     match (true, false) {

src/test/compile-fail/issue-7061.rs

@@ -13,7 +13,7 @@ struct BarStruct;
 impl<'a> BarStruct {
     fn foo(&'a mut self) -> Box<BarStruct> { self }
     //~^ ERROR mismatched types
-    //~| expected type `std::boxed::Box<BarStruct>`
+    //~| expected type `Box<BarStruct>`
     //~| found type `&'a mut BarStruct`
 }
 

src/test/compile-fail/issue-7092.rs

@@ -16,7 +16,7 @@ fn foo(x: Whatever) {
         Some(field) =>
 //~^ ERROR mismatched types
 //~| expected type `Whatever`
-//~| found type `std::option::Option<_>`
+//~| found type `Option<_>`
 //~| expected enum `Whatever`, found enum `std::option::Option`
             field.access(),
     }

src/test/compile-fail/issue-7867.rs

@@ -25,13 +25,13 @@ fn main() {
     match &Some(42) {
         Some(x) => (),
         //~^ ERROR mismatched types
-        //~| expected type `&std::option::Option<{integer}>`
-        //~| found type `std::option::Option<_>`
+        //~| expected type `&Option<{integer}>`
+        //~| found type `Option<_>`
         //~| expected reference, found enum `std::option::Option`
         None => ()
         //~^ ERROR mismatched types
-        //~| expected type `&std::option::Option<{integer}>`
-        //~| found type `std::option::Option<_>`
+        //~| expected type `&Option<{integer}>`
+        //~| found type `Option<_>`
         //~| expected reference, found enum `std::option::Option`
     }
 }

src/test/compile-fail/noexporttypeexe.rs

@@ -20,6 +20,6 @@ fn main() {
   let x: isize = noexporttypelib::foo();
     //~^ ERROR mismatched types
     //~| expected type `isize`
-    //~| found type `std::option::Option<isize>`
+    //~| found type `Option<isize>`
     //~| expected isize, found enum `std::option::Option`
 }

src/test/compile-fail/occurs-check-2.rs

@@ -17,6 +17,6 @@ fn main() {
     f = box g;
     //~^  ERROR mismatched types
     //~| expected type `_`
-    //~| found type `std::boxed::Box<_>`
+    //~| found type `Box<_>`
     //~| cyclic type of infinite size
 }

src/test/compile-fail/occurs-check.rs

@@ -15,6 +15,6 @@ fn main() {
     f = box f;
     //~^ ERROR mismatched types
     //~| expected type `_`
-    //~| found type `std::boxed::Box<_>`
+    //~| found type `Box<_>`
     //~| cyclic type of infinite size
 }

src/test/compile-fail/regions-infer-paramd-indirect.rs

@@ -32,8 +32,8 @@ impl<'a> set_f<'a> for c<'a> {
     fn set_f_bad(&mut self, b: Box<b>) {
         self.f = b;
         //~^ ERROR mismatched types
-        //~| expected type `std::boxed::Box<std::boxed::Box<&'a isize>>`
-        //~| found type `std::boxed::Box<std::boxed::Box<&isize>>`
+        //~| expected type `Box<Box<&'a isize>>`
+        //~| found type `Box<Box<&isize>>`
         //~| lifetime mismatch
     }
 }

src/test/compile-fail/tag-that-dare-not-speak-its-name.rs

@@ -22,6 +22,6 @@ fn main() {
     let x : char = last(y);
     //~^ ERROR mismatched types
     //~| expected type `char`
-    //~| found type `std::option::Option<_>`
+    //~| found type `Option<_>`
     //~| expected char, found enum `std::option::Option`
 }

src/test/compile-fail/terr-sorts.rs

@@ -20,7 +20,7 @@ fn want_foo(f: foo) {}
 fn have_bar(b: bar) {
     want_foo(b); //~  ERROR mismatched types
                  //~| expected type `foo`
-                 //~| found type `std::boxed::Box<foo>`
+                 //~| found type `Box<foo>`
 }
 
 fn main() {}

src/test/compile-fail/type-mismatch-same-crate-name.rs

@@ -33,7 +33,7 @@ fn main() {
         //~^ ERROR mismatched types
         //~| Perhaps two different versions of crate `crate_a1`
         //~| expected trait `main::a::Bar`
-        //~| expected type `std::boxed::Box<main::a::Bar + 'static>`
-        //~| found type `std::boxed::Box<main::a::Bar>`
+        //~| expected type `Box<main::a::Bar + 'static>`
+        //~| found type `Box<main::a::Bar>`
     }
 }

src/test/ui/block-result/consider-removing-last-semi.stderr

@@ -9,7 +9,7 @@ error[E0308]: mismatched types
 14 | | }
    | |_^ expected struct `std::string::String`, found ()
    |
-   = note: expected type `std::string::String`
+   = note: expected type `String`
               found type `()`
 
 error[E0308]: mismatched types
@@ -23,7 +23,7 @@ error[E0308]: mismatched types
 19 | | }
    | |_^ expected struct `std::string::String`, found ()
    |
-   = note: expected type `std::string::String`
+   = note: expected type `String`
               found type `()`
 
 error: aborting due to 2 previous errors

src/test/ui/block-result/issue-13428.stderr

@@ -12,7 +12,7 @@ error[E0308]: mismatched types
 19 | | }
    | |_^ expected struct `std::string::String`, found ()
    |
-   = note: expected type `std::string::String`
+   = note: expected type `String`
               found type `()`
 
 error[E0308]: mismatched types
@@ -26,7 +26,7 @@ error[E0308]: mismatched types
 24 | | }
    | |_^ expected struct `std::string::String`, found ()
    |
-   = note: expected type `std::string::String`
+   = note: expected type `String`
               found type `()`
 
 error: aborting due to 2 previous errors

src/test/ui/coercion-missing-tail-expected-type.stderr

@@ -21,7 +21,7 @@ error[E0308]: mismatched types
 19 | | }
    | |_^ expected enum `std::result::Result`, found ()
    |
-   = note: expected type `std::result::Result<u8, u64>`
+   = note: expected type `Result<u8, u64>`
               found type `()`
 
 error: aborting due to 2 previous errors

src/test/ui/lifetime-errors/ex2d-push-inference-variable-2.stderr

@@ -27,7 +27,7 @@ note: but, the lifetime must be valid for the lifetime 'b as defined on the func
 18 | |     a.push(b);
 19 | | }
    | |_^
-note: ...so that expression is assignable (expected &mut std::vec::Vec<Ref<'_, i32>>, found &mut std::vec::Vec<Ref<'b, i32>>)
+note: ...so that expression is assignable (expected &mut Vec<Ref<'_, i32>>, found &mut Vec<Ref<'b, i32>>)
   --> $DIR/ex2d-push-inference-variable-2.rs:16:33
    |
 16 |     let a: &mut Vec<Ref<i32>> = x;

src/test/ui/lifetime-errors/ex2e-push-inference-variable-3.stderr

@@ -27,7 +27,7 @@ note: but, the lifetime must be valid for the lifetime 'b as defined on the func
 18 | |     Vec::push(a, b);
 19 | | }
    | |_^
-note: ...so that expression is assignable (expected &mut std::vec::Vec<Ref<'_, i32>>, found &mut std::vec::Vec<Ref<'b, i32>>)
+note: ...so that expression is assignable (expected &mut Vec<Ref<'_, i32>>, found &mut Vec<Ref<'b, i32>>)
   --> $DIR/ex2e-push-inference-variable-3.rs:16:33
    |
 16 |     let a: &mut Vec<Ref<i32>> = x;

src/test/ui/local-ident.rs

@@ -0,0 +1,25 @@
+// 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.
+
+use Mod1::S;
+use Mod2::*;
+
+fn main() {
+    let x: X = S;
+    let y: Option<usize> = Ok(2);
+}
+
+mod Mod1 {
+    pub struct S;
+}
+
+mod Mod2 {
+    pub struct X;
+}

src/test/ui/local-ident.stderr

@@ -0,0 +1,24 @@
+error[E0308]: mismatched types
+  --> $DIR/local-ident.rs:15:16
+   |
+15 |     let x: X = S;
+   |                ^ expected struct `Mod2::X`, found struct `Mod1::S`
+   |
+   = note: expected type `X`
+              found type `S`
+
+error[E0308]: mismatched types
+  --> $DIR/local-ident.rs:16:28
+   |
+16 |     let y: Option<usize> = Ok(2);
+   |                            ^^^^^ expected enum `std::option::Option`, found enum `std::result::Result`
+   |
+   = note: expected type `Option<usize>`
+              found type `Result<{integer}, _>`
+   = help: here are some functions which might fulfill your needs:
+           - .err()
+           - .ok()
+           - .unwrap_err()
+
+error: aborting due to 2 previous errors
+