Description
Summary
cast_possible_truncation pedantically fires for any u64 -> usize conversion with no respect to the target platforms.
Some projects may have no need to support 32-bit platforms while still wanting to use the cast_possible_truncation for the other cases of possible truncation. However, the u64 -> usize warning becomes increasingly noisy in codebases that deal with with filesystems and similar APIs so the entire lint ends up allowed.
Therefore, I feel it's reasonable to say cast_possible_truncation has overly broad scope. The " on targets with 32-bit wide pointers" suffix appended to the warning lends to it being overly broad by acknowledging that it may be firing unnecessarily.
I would like to keep cast_possible_truncation enabled in my codebase but have it be silent when casting u64 -> usize when my target is also 64-bit. Lints are target agnostic, so perhaps we can split cast_possible_truncation into a separate warning when u64 -> usize. And maybe also usize -> u32 for the inverse reason.
Reproducer
// target_pointer_width = "64" not necessary but included to illustrate the overbroadness
#[cfg(target_pointer_width = "64")]
#[deny(clippy::cast_possible_truncation)]
const fn thunk(v: u64) -> usize {
v as usize
}Version
rustc 1.90.0-nightly (f26e58023 2025-06-30)
binary: rustc
commit-hash: f26e58023071e71636a3c72ac3a2bf89b1f76706
commit-date: 2025-06-30
host: aarch64-apple-darwin
release: 1.90.0-nightly
LLVM version: 20.1.7
Additional Labels
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