Suggest try_into when possible

src/librustc/hir/map/mod.rs

@@ -734,6 +734,14 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    pub fn is_const_scope(&self, hir_id: HirId) -> bool {
+        self.walk_parent_nodes(hir_id, |node| match *node {
+            Node::Item(Item { node: ItemKind::Const(_, _), .. }) => true,
+            Node::Item(Item { node: ItemKind::Fn(_, header, _, _), .. }) => header.is_const(),
+            _ => false,
+        }, |_| false).map(|id| id != CRATE_HIR_ID).unwrap_or(false)
+    }
+
     /// If there is some error when walking the parents (e.g., a node does not
     /// have a parent in the map or a node can't be found), then we return the
     /// last good `NodeId` we found. Note that reaching the crate root (`id == 0`),

src/librustc/hir/mod.rs

@@ -2288,6 +2288,15 @@ pub struct FnHeader {
     pub abi: Abi,
 }
 
+impl FnHeader {
+    pub fn is_const(&self) -> bool {
+        match &self.constness {
+            Constness::Const => true,
+            _ => false,
+        }
+    }
+}
+
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug, HashStable)]
 pub enum ItemKind {
     /// An `extern crate` item, with optional *original* crate name if the crate was renamed.

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

@@ -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/discrim/discrim-ill-typed.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/float-literal-inference-restrictions.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/indexing-requires-a-uint.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