Reword when _ couldn't be inferred

Author: Esteban Küber

src/librustc/infer/error_reporting/need_type_info.rs

@@ -96,7 +96,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let name = self.extract_type_name(&ty);
 
         let mut err_span = span;
-        let mut labels = vec![(span, format!("cannot infer type for `{}`", name))];
+        let mut labels = vec![(
+            span,
+            if &name == "_" {
+                "cannot infer type".to_string()
+            } else {
+                format!("cannot infer type for `{}`", name)
+            },
+        )];
 
         let mut local_visitor = FindLocalByTypeVisitor {
             infcx: &self,

src/test/ui/error-codes/E0282.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let x = "hello".chars().rev().collect(); //~ ERROR E0282
    |         ^
    |         |
-   |         cannot infer type for `_`
+   |         cannot infer type
    |         consider giving `x` a type
 
 error: aborting due to previous error

src/test/ui/issue-12187-1.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let &v = new();
    |         -^
    |         ||
-   |         |cannot infer type for `_`
+   |         |cannot infer type
    |         consider giving the pattern a type
 
 error: aborting due to previous error

src/test/ui/issue-12187-2.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let &v = new();
    |         -^
    |         ||
-   |         |cannot infer type for `_`
+   |         |cannot infer type
    |         consider giving the pattern a type
 
 error: aborting due to previous error

src/test/ui/issue-15965.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL | /         { return () }
 LL | | //~^ ERROR type annotations needed [E0282]
 LL | |     ()
-   | |______^ cannot infer type for `_`
+   | |______^ cannot infer type
    |
    = note: type must be known at this point
 

src/test/ui/issue-18159.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let x; //~ ERROR type annotations needed
    |         ^
    |         |
-   |         cannot infer type for `_`
+   |         cannot infer type
    |         consider giving `x` a type
 
 error: aborting due to previous error

src/test/ui/issue-20261.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     for (ref i,) in [].iter() {
    |         -------- consider giving `__next` a type
 LL |         i.clone();
-   |           ^^^^^ cannot infer type for `_`
+   |           ^^^^^ cannot infer type
    |
    = note: type must be known at this point
 

src/test/ui/issue-2151.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let x = panic!();
    |         - consider giving `x` a type
 LL |     x.clone(); //~ ERROR type annotations needed
-   |     ^ cannot infer type for `_`
+   |     ^ cannot infer type
    |
    = note: type must be known at this point
 

src/test/ui/issue-23041.stderr

@@ -2,7 +2,7 @@ error[E0282]: type annotations needed
   --> $DIR/issue-23041.rs:16:22
    |
 LL |     b.downcast_ref::<fn(_)->_>(); //~ ERROR E0282
-   |                      ^^^^^^^^ cannot infer type for `_`
+   |                      ^^^^^^^^ cannot infer type
 
 error: aborting due to previous error
 

src/test/ui/issue-24013.stderr

@@ -2,7 +2,7 @@ error[E0282]: type annotations needed
   --> $DIR/issue-24013.rs:15:20
    |
 LL |     unsafe {swap::<&mut _>(transmute(&a), transmute(&b))};
-   |                    ^^^^^^ cannot infer type for `_`
+   |                    ^^^^^^ cannot infer type
 
 error: aborting due to previous error
 

src/test/ui/issue-7813.stderr

@@ -2,7 +2,7 @@ error[E0282]: type annotations needed
   --> $DIR/issue-7813.rs:12:13
    |
 LL |     let v = &[]; //~ ERROR type annotations needed
-   |         -   ^^^ cannot infer type for `_`
+   |         -   ^^^ cannot infer type
    |         |
    |         consider giving `v` a type
 

src/test/ui/span/issue-42234-unknown-receiver-type.stderr

@@ -13,7 +13,7 @@ error[E0282]: type annotations needed
    |
 LL | /     data.iter() //~ ERROR 22:5: 23:20: type annotations needed
 LL | |         .sum::<_>()
-   | |___________________^ cannot infer type for `_`
+   | |___________________^ cannot infer type
    |
    = note: type must be known at this point
 

src/test/ui/span/method-and-field-eager-resolution.stderr

@@ -4,7 +4,7 @@ error[E0282]: type annotations needed
 LL |     let mut x = Default::default();
    |         ----- consider giving `x` a type
 LL |     x.0;
-   |     ^ cannot infer type for `_`
+   |     ^ cannot infer type
    |
    = note: type must be known at this point
 
@@ -14,7 +14,7 @@ error[E0282]: type annotations needed
 LL |     let mut x = Default::default();
    |         ----- consider giving `x` a type
 LL |     x[0];
-   |     ^ cannot infer type for `_`
+   |     ^ cannot infer type
    |
    = note: type must be known at this point
 

src/test/ui/type-check/cannot_infer_local_or_array.stderr

@@ -2,7 +2,7 @@ error[E0282]: type annotations needed
   --> $DIR/cannot_infer_local_or_array.rs:12:13
    |
 LL |     let x = []; //~ ERROR type annotations needed
-   |         -   ^^ cannot infer type for `_`
+   |         -   ^^ cannot infer type
    |         |
    |         consider giving `x` a type