Suggest try_into when possible

Author: estebank

src/librustc_typeck/check/demand.rs

@@ -3,6 +3,10 @@ error[E0308]: mismatched types
    |
 LL |     f1(2i32, 4i32);
    |              ^^^^ expected u32, found i32
+help: change the type of the numeric literal from `i32` to `u32`
+   |
+LL |     f1(2i32, 4u32);
+   |              ^^^^
 
 error[E0277]: the trait bound `u32: Foo` is not satisfied
   --> $DIR/associated-types-path-2.rs:29:5
@@ -45,6 +49,10 @@ error[E0308]: mismatched types
    |
 LL |     let _: i32 = f2(2i32);
    |                  ^^^^^^^^ expected i32, found u32
+help: you can convert an `u32` to `i32` or panic if it the converted value wouldn't fit
+   |
+LL |     let _: i32 = f2(2i32).try_into().unwrap();
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 6 previous errors
 

src/test/ui/associated-types/associated-types-path-2.stderr

@@ -3,48 +3,80 @@ error[E0308]: mismatched types
    |
 LL |         OhNo = 0_u8,
    |                ^^^^ expected i8, found u8
+help: change the type of the numeric literal from `u8` to `i8`
+   |
+LL |         OhNo = 0_i8,
+   |                ^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:30:16
    |
 LL |         OhNo = 0_i8,
    |                ^^^^ expected u8, found i8
+help: change the type of the numeric literal from `i8` to `u8`
+   |
+LL |         OhNo = 0_u8,
+   |                ^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:43:16
    |
 LL |         OhNo = 0_u16,
    |                ^^^^^ expected i16, found u16
+help: change the type of the numeric literal from `u16` to `i16`
+   |
+LL |         OhNo = 0_i16,
+   |                ^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:56:16
    |
 LL |         OhNo = 0_i16,
    |                ^^^^^ expected u16, found i16
+help: change the type of the numeric literal from `i16` to `u16`
+   |
+LL |         OhNo = 0_u16,
+   |                ^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:69:16
    |
 LL |         OhNo = 0_u32,
    |                ^^^^^ expected i32, found u32
+help: change the type of the numeric literal from `u32` to `i32`
+   |
+LL |         OhNo = 0_i32,
+   |                ^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:82:16
    |
 LL |         OhNo = 0_i32,
    |                ^^^^^ expected u32, found i32
+help: change the type of the numeric literal from `i32` to `u32`
+   |
+LL |         OhNo = 0_u32,
+   |                ^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:95:16
    |
 LL |         OhNo = 0_u64,
    |                ^^^^^ expected i64, found u64
+help: change the type of the numeric literal from `u64` to `i64`
+   |
+LL |         OhNo = 0_i64,
+   |                ^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/discrim-ill-typed.rs:108:16
    |
 LL |         OhNo = 0_i64,
    |                ^^^^^ expected u64, found i64
+help: change the type of the numeric literal from `i64` to `u64`
+   |
+LL |         OhNo = 0_u64,
+   |                ^^^^^
 
 error: aborting due to 8 previous errors
 

src/test/ui/discrim/discrim-ill-typed.stderr

@@ -15,6 +15,10 @@ error[E0308]: mismatched types
    |
 LL |     let y: f32 = 1f64;
    |                  ^^^^ expected f32, found f64
+help: change the type of the numeric literal from `f64` to `f32`
+   |
+LL |     let y: f32 = 1f32;
+   |                  ^^^^
 
 error: aborting due to 2 previous errors
 

src/test/ui/float-literal-inference-restrictions.stderr

@@ -12,6 +12,10 @@ error[E0308]: mismatched types
    |
 LL |     bar::<isize>(i);  // i should not be re-coerced back to an isize
    |                  ^ expected isize, found usize
+help: you can convert an `usize` to `isize` or panic if it the converted value wouldn't fit
+   |
+LL |     bar::<isize>(i.try_into().unwrap());  // i should not be re-coerced back to an isize
+   |                  ^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 2 previous errors