`cast_possible_truncation`: `x.min(C) as T` is only recognized when `C` is a literal

Summary

cast_possible_truncation knows that x.min(C) bounds the value, but only when C is a literal. With the same bound written as u32::MAX as u64, u32::MAX.into() or u64::from(u32::MAX) it still fires. The last form is what cast_lossless suggests for u32::MAX as u64, so following the suggestion of one lint keeps this one firing.

Related: #9613.

Lint Name

cast_possible_truncation

Reproducer

I tried this code:

#![warn(clippy::cast_possible_truncation)]

pub fn literal(x: u64) -> u32 {
    x.min(0xFFFF_FFFF) as u32
}

pub fn cast(x: u64) -> u32 {
    x.min(u32::MAX as u64) as u32
}

pub fn into(x: u64) -> u32 {
    x.min(u32::MAX.into()) as u32
}

pub fn from(x: u64) -> u32 {
    x.min(u64::from(u32::MAX)) as u32
}

I saw this happen:

warning: casting `u64` to `u32` may truncate the value
 --> lib.rs:8:5
  |
8 |     x.min(u32::MAX as u64) as u32
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
  = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.98.0/index.html#cast_possible_truncation
note: the lint level is defined here
 --> lib.rs:1:9
  |
1 | #![warn(clippy::cast_possible_truncation)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: ... or use `try_from` and handle the error accordingly
  |
8 -     x.min(u32::MAX as u64) as u32
8 +     u32::try_from(x.min(u32::MAX as u64))
  |

warning: casting `u64` to `u32` may truncate the value
  --> lib.rs:12:5
   |
12 |     x.min(u32::MAX.into()) as u32
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
   = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.98.0/index.html#cast_possible_truncation
help: ... or use `try_from` and handle the error accordingly
   |
12 -     x.min(u32::MAX.into()) as u32
12 +     u32::try_from(x.min(u32::MAX.into()))
   |

warning: casting `u64` to `u32` may truncate the value
  --> lib.rs:16:5
   |
16 |     x.min(u64::from(u32::MAX)) as u32
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
   = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.98.0/index.html#cast_possible_truncation
help: ... or use `try_from` and handle the error accordingly
   |
16 -     x.min(u64::from(u32::MAX)) as u32
16 +     u32::try_from(x.min(u64::from(u32::MAX)))
   |

I expected to see this happen: No warning in any of the four functions, as in literal: the value is bounded by u32::MAX before the cast.

Version

rustc 1.98.0 (88d9e12ae 2026-08-18)
binary: rustc
commit-hash: 88d9e12ae178fab0fb5cc050a94da85685d449ea
commit-date: 2026-08-18
host: x86_64-pc-windows-msvc
release: 1.98.0
LLVM version: 22.1.8

Use the cast_possible_truncation lint as the entry point and reproduce the four functions shown in the issue. Trace how bounds from u32::MAX as u64, .into(), and u64::from are recognized, then verify that all four forms avoid the warning while the existing literal case remains unchanged.