Disable cast_lossless when casting to u128 from any (u)int type

clippy_lints/src/casts/cast_lossless.rs

@@ -6,7 +6,7 @@ use clippy_utils::ty::is_isize_or_usize;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, QPath, TyKind};
 use rustc_lint::LateContext;
-use rustc_middle::ty::{self, FloatTy, Ty};
+use rustc_middle::ty::{self, FloatTy, Ty, UintTy};
 
 use super::{utils, CAST_LOSSLESS};
 
@@ -77,7 +77,10 @@ pub(super) fn check(
 
 fn should_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>, msrv: &Msrv) -> bool {
     // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
-    if in_constant(cx, expr.hir_id) {
+    //
+    // If destination is u128, do not lint because source type cannot be larger
+    // If source is bool, still lint due to the lint message differing (refers to style)
+    if in_constant(cx, expr.hir_id) || (!cast_from.is_bool() && matches!(cast_to.kind(), ty::Uint(UintTy::U128))) {
         return false;
     }
 

tests/ui/cast_lossless_integer.fixed

@@ -2,6 +2,7 @@
 #![warn(clippy::cast_lossless)]
 
 type I64 = i64;
+type U128 = u128;
 
 fn main() {
     // Test clippy::cast_lossless with casts to integer types
@@ -28,6 +29,11 @@ fn main() {
     let _ = u16::from(1u8 + 1u8);
 
     let _ = I64::from(1i8);
+
+    // Do not lint if destination type is u128
+    // see https://github.com/rust-lang/rust-clippy/issues/12492
+    let _ = 1u8 as u128;
+    let _ = 1u8 as U128;
 }
 
 // The lint would suggest using `f64::from(input)` here but the `XX::from` function is not const,

tests/ui/cast_lossless_integer.rs

@@ -2,6 +2,7 @@
 #![warn(clippy::cast_lossless)]
 
 type I64 = i64;
+type U128 = u128;
 
 fn main() {
     // Test clippy::cast_lossless with casts to integer types
@@ -28,6 +29,11 @@ fn main() {
     let _ = (1u8 + 1u8) as u16;
 
     let _ = 1i8 as I64;
+
+    // Do not lint if destination type is u128
+    // see https://github.com/rust-lang/rust-clippy/issues/12492
+    let _ = 1u8 as u128;
+    let _ = 1u8 as U128;
 }
 
 // The lint would suggest using `f64::from(input)` here but the `XX::from` function is not const,

tests/ui/cast_lossless_integer.stderr

@@ -1,5 +1,5 @@
 error: casting `i8` to `i16` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:8:13
+  --> tests/ui/cast_lossless_integer.rs:9:13
    |
 LL |     let _ = 1i8 as i16;
    |             ^^^^^^^^^^ help: try: `i16::from(1i8)`
@@ -8,127 +8,127 @@ LL |     let _ = 1i8 as i16;
    = help: to override `-D warnings` add `#[allow(clippy::cast_lossless)]`
 
 error: casting `i8` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:9:13
+  --> tests/ui/cast_lossless_integer.rs:10:13
    |
 LL |     let _ = 1i8 as i32;
    |             ^^^^^^^^^^ help: try: `i32::from(1i8)`
 
 error: casting `i8` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:10:13
+  --> tests/ui/cast_lossless_integer.rs:11:13
    |
 LL |     let _ = 1i8 as i64;
    |             ^^^^^^^^^^ help: try: `i64::from(1i8)`
 
 error: casting `u8` to `i16` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:11:13
+  --> tests/ui/cast_lossless_integer.rs:12:13
    |
 LL |     let _ = 1u8 as i16;
    |             ^^^^^^^^^^ help: try: `i16::from(1u8)`
 
 error: casting `u8` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:12:13
+  --> tests/ui/cast_lossless_integer.rs:13:13
    |
 LL |     let _ = 1u8 as i32;
    |             ^^^^^^^^^^ help: try: `i32::from(1u8)`
 
 error: casting `u8` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:13:13
+  --> tests/ui/cast_lossless_integer.rs:14:13
    |
 LL |     let _ = 1u8 as i64;
    |             ^^^^^^^^^^ help: try: `i64::from(1u8)`
 
 error: casting `u8` to `u16` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:14:13
+  --> tests/ui/cast_lossless_integer.rs:15:13
    |
 LL |     let _ = 1u8 as u16;
    |             ^^^^^^^^^^ help: try: `u16::from(1u8)`
 
 error: casting `u8` to `u32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:15:13
+  --> tests/ui/cast_lossless_integer.rs:16:13
    |
 LL |     let _ = 1u8 as u32;
    |             ^^^^^^^^^^ help: try: `u32::from(1u8)`
 
 error: casting `u8` to `u64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:16:13
+  --> tests/ui/cast_lossless_integer.rs:17:13
    |
 LL |     let _ = 1u8 as u64;
    |             ^^^^^^^^^^ help: try: `u64::from(1u8)`
 
 error: casting `i16` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:17:13
+  --> tests/ui/cast_lossless_integer.rs:18:13
    |
 LL |     let _ = 1i16 as i32;
    |             ^^^^^^^^^^^ help: try: `i32::from(1i16)`
 
 error: casting `i16` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:18:13
+  --> tests/ui/cast_lossless_integer.rs:19:13
    |
 LL |     let _ = 1i16 as i64;
    |             ^^^^^^^^^^^ help: try: `i64::from(1i16)`
 
 error: casting `u16` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:19:13
+  --> tests/ui/cast_lossless_integer.rs:20:13
    |
 LL |     let _ = 1u16 as i32;
    |             ^^^^^^^^^^^ help: try: `i32::from(1u16)`
 
 error: casting `u16` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:20:13
+  --> tests/ui/cast_lossless_integer.rs:21:13
    |
 LL |     let _ = 1u16 as i64;
    |             ^^^^^^^^^^^ help: try: `i64::from(1u16)`
 
 error: casting `u16` to `u32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:21:13
+  --> tests/ui/cast_lossless_integer.rs:22:13
    |
 LL |     let _ = 1u16 as u32;
    |             ^^^^^^^^^^^ help: try: `u32::from(1u16)`
 
 error: casting `u16` to `u64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:22:13
+  --> tests/ui/cast_lossless_integer.rs:23:13
    |
 LL |     let _ = 1u16 as u64;
    |             ^^^^^^^^^^^ help: try: `u64::from(1u16)`
 
 error: casting `i32` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:23:13
+  --> tests/ui/cast_lossless_integer.rs:24:13
    |
 LL |     let _ = 1i32 as i64;
    |             ^^^^^^^^^^^ help: try: `i64::from(1i32)`
 
 error: casting `u32` to `i64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:24:13
+  --> tests/ui/cast_lossless_integer.rs:25:13
    |
 LL |     let _ = 1u32 as i64;
    |             ^^^^^^^^^^^ help: try: `i64::from(1u32)`
 
 error: casting `u32` to `u64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:25:13
+  --> tests/ui/cast_lossless_integer.rs:26:13
    |
 LL |     let _ = 1u32 as u64;
    |             ^^^^^^^^^^^ help: try: `u64::from(1u32)`
 
 error: casting `u8` to `u16` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:28:13
+  --> tests/ui/cast_lossless_integer.rs:29:13
    |
 LL |     let _ = (1u8 + 1u8) as u16;
    |             ^^^^^^^^^^^^^^^^^^ help: try: `u16::from(1u8 + 1u8)`
 
 error: casting `i8` to `I64` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:30:13
+  --> tests/ui/cast_lossless_integer.rs:31:13
    |
 LL |     let _ = 1i8 as I64;
    |             ^^^^^^^^^^ help: try: `I64::from(1i8)`
 
 error: casting `i8` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:64:13
+  --> tests/ui/cast_lossless_integer.rs:70:13
    |
 LL |     let _ = sign_cast!(x, u8, i8) as i32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `i32::from(sign_cast!(x, u8, i8))`
 
 error: casting `i8` to `i32` may become silently lossy if you later change the type
-  --> tests/ui/cast_lossless_integer.rs:65:13
+  --> tests/ui/cast_lossless_integer.rs:71:13
    |
 LL |     let _ = (sign_cast!(x, u8, i8) + 1) as i32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `i32::from(sign_cast!(x, u8, i8) + 1)`