Suggest .into() over try_into() when it would work

src/librustc_typeck/check/demand.rs

@@ -753,17 +753,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             match (&expected_ty.kind, &checked_ty.kind) {
                 (&ty::Int(ref exp), &ty::Int(ref found)) => {
-                    let is_fallible = match (found.bit_width(), exp.bit_width()) {
-                        (Some(found), Some(exp)) if found > exp => true,
+                    let is_fallible = match (exp.bit_width(), found.bit_width()) {
+                        (Some(exp), Some(found)) if exp < found => true,
+                        (None, Some(8 | 16)) => false,
                         (None, _) | (_, None) => true,
                         _ => false,
                     };
                     suggest_to_change_suffix_or_into(err, is_fallible);
                     true
                 }
                 (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
-                    let is_fallible = match (found.bit_width(), exp.bit_width()) {
-                        (Some(found), Some(exp)) if found > exp => true,
+                    let is_fallible = match (exp.bit_width(), found.bit_width()) {
+                        (Some(exp), Some(found)) if exp < found => true,
+                        (None, Some(8 | 16)) => false,
                         (None, _) | (_, None) => true,
                         _ => false,
                     };

src/test/ui/integer-literal-suffix-inference.rs

@@ -16,6 +16,7 @@ fn main() {
     fn id_i16(n: i16) -> i16 { n }
     fn id_i32(n: i32) -> i32 { n }
     fn id_i64(n: i64) -> i64 { n }
+    fn id_isize(n: isize) -> isize { n }
 
     // the smallest values that need these types
     let b8: u8 = 16;
@@ -27,6 +28,11 @@ fn main() {
     fn id_u16(n: u16) -> u16 { n }
     fn id_u32(n: u32) -> u32 { n }
     fn id_u64(n: u64) -> u64 { n }
+    fn id_usize(n: usize) -> usize { n }
+
+    // Values for testing *size
+    let asize: isize = 1;
+    let bsize: usize = 3;
 
     id_i8(a8); // ok
     id_i8(a16);
@@ -38,6 +44,9 @@ fn main() {
     id_i8(a64);
     //~^ ERROR mismatched types
     //~| expected `i8`, found `i64`
+    id_i8(asize);
+    //~^ ERROR mismatched types
+    //~| expected `i8`, found `isize`
 
     id_i16(a8);
     //~^ ERROR mismatched types
@@ -49,6 +58,9 @@ fn main() {
     id_i16(a64);
     //~^ ERROR mismatched types
     //~| expected `i16`, found `i64`
+    id_i16(asize);
+    //~^ ERROR mismatched types
+    //~| expected `i16`, found `isize`
 
     id_i32(a8);
     //~^ ERROR mismatched types
@@ -60,6 +72,9 @@ fn main() {
     id_i32(a64);
     //~^ ERROR mismatched types
     //~| expected `i32`, found `i64`
+    id_i32(asize);
+    //~^ ERROR mismatched types
+    //~| expected `i32`, found `isize`
 
     id_i64(a8);
     //~^ ERROR mismatched types
@@ -71,6 +86,23 @@ fn main() {
     //~^ ERROR mismatched types
     //~| expected `i64`, found `i32`
     id_i64(a64); // ok
+    id_i64(asize);
+    //~^ ERROR mismatched types
+    //~| expected `i64`, found `isize`
+
+    id_isize(a8);
+    //~^ ERROR mismatched types
+    //~| expected `isize`, found `i8`
+    id_isize(a16);
+    //~^ ERROR mismatched types
+    //~| expected `isize`, found `i16`
+    id_isize(a32);
+    //~^ ERROR mismatched types
+    //~| expected `isize`, found `i32`
+    id_isize(a64);
+    //~^ ERROR mismatched types
+    //~| expected `isize`, found `i64`
+    id_isize(asize); //ok
 
     id_i8(c8); // ok
     id_i8(c16);
@@ -126,6 +158,9 @@ fn main() {
     id_u8(b64);
     //~^ ERROR mismatched types
     //~| expected `u8`, found `u64`
+    id_u8(bsize);
+    //~^ ERROR mismatched types
+    //~| expected `u8`, found `usize`
 
     id_u16(b8);
     //~^ ERROR mismatched types
@@ -137,6 +172,9 @@ fn main() {
     id_u16(b64);
     //~^ ERROR mismatched types
     //~| expected `u16`, found `u64`
+    id_u16(bsize);
+    //~^ ERROR mismatched types
+    //~| expected `u16`, found `usize`
 
     id_u32(b8);
     //~^ ERROR mismatched types
@@ -148,6 +186,9 @@ fn main() {
     id_u32(b64);
     //~^ ERROR mismatched types
     //~| expected `u32`, found `u64`
+    id_u32(bsize);
+    //~^ ERROR mismatched types
+    //~| expected `u32`, found `usize`
 
     id_u64(b8);
     //~^ ERROR mismatched types
@@ -159,4 +200,21 @@ fn main() {
     //~^ ERROR mismatched types
     //~| expected `u64`, found `u32`
     id_u64(b64); // ok
+    id_u64(bsize);
+    //~^ ERROR mismatched types
+    //~| expected `u64`, found `usize`
+
+    id_usize(b8);
+    //~^ ERROR mismatched types
+    //~| expected `usize`, found `u8`
+    id_usize(b16);
+    //~^ ERROR mismatched types
+    //~| expected `usize`, found `u16`
+    id_usize(b32);
+    //~^ ERROR mismatched types
+    //~| expected `usize`, found `u32`
+    id_usize(b64);
+    //~^ ERROR mismatched types
+    //~| expected `usize`, found `u64`
+    id_usize(bsize); //ok
 }