Suggest the smallest fitting type instead

Changes the behavior of the `overflowing_literals` suggestion so that it
always suggest the smallest type regardless of the original type size.

compiler/rustc_lint/src/types/literal.rs

@@ -204,14 +204,14 @@ fn get_type_suggestion(t: Ty<'_>, val: u128, negative: bool) -> Option<&'static
     match t.kind() {
         ty::Uint(ty::UintTy::Usize) | ty::Int(ty::IntTy::Isize) => None,
         ty::Uint(_) => Some(Integer::fit_unsigned(val).uint_ty_str()),
-        ty::Int(int) => {
+        ty::Int(_) => {
             let signed = literal_to_i128(val, negative).map(Integer::fit_signed);
             if negative {
                 signed.map(Integer::int_ty_str)
             } else {
                 let unsigned = Integer::fit_unsigned(val);
                 Some(if let Some(signed) = signed {
-                    if Some(unsigned.size().bits()) == int.bit_width() {
+                    if unsigned.size() < signed.size() {
                         unsigned.uint_ty_str()
                     } else {
                         signed.int_ty_str()

tests/ui/lint/type-overflow.rs

@@ -40,7 +40,7 @@ fn main() {
     //~| HELP consider using the type `u128` instead
 
     let fail = 0x8FFF_FFFF_FFFF_FFFE; //~WARNING literal out of range for `i32`
-    //~| HELP consider using the type `i128` instead
+    //~| HELP consider using the type `u64` instead
     //~| HELP
 
     let fail = -0b1111_1111i8; //~WARNING literal out of range for `i8`

tests/ui/lint/type-overflow.stderr

@@ -109,7 +109,7 @@ LL |     let fail = 0x8FFF_FFFF_FFFF_FFFE;
    |                ^^^^^^^^^^^^^^^^^^^^^
    |
    = note: the literal `0x8FFF_FFFF_FFFF_FFFE` (decimal `10376293541461622782`) does not fit into the type `i32` and will become `-2i32`
-   = help: consider using the type `i128` instead
+   = help: consider using the type `u64` instead
 help: to use as a negative number (decimal `-2`), consider using the type `u32` for the literal and cast it to `i32`
    |
 LL |     let fail = 0x8FFF_FFFF_FFFF_FFFEu32 as i32;