cast_lossless on const item

[letheed]

const FOO: i32 = 42;
const FOO_I64: i64 = 42 as i64;

Triggers the suggestion try: i64::from(FOO) which isn't possible (yet?).

[oli-obk]

I cannot reproduce on the playpen. Are you sure you're running the latest clippy?

[letheed]

My mistake I meant:

const FOO: i32 = 42;
const FOO_I64: i64 = FOO as i64;

[oli-obk]

We should not be doing this suggestion inside constants until From/Into are usable in constants

[oli-obk]

Just needs a regression test

[cipriancraciun]

I just got this suggestion when I use value as u64 (where value is u32), but when used in a const fn.

I assume this is a regression?

(I'm using latest clippy (0.0.211) and rust-nightly.)

    pub const fn for_builtin (handle : u32) -> (Handle) {
        return Handle ( handle as u64 );
    }

error: casting u32 to u64 may become silently lossy if types change
   --> sources/runtime.rs:211:19
    |
211 |         return Handle ( handle as u64 );
    |                         ^^^^^^^^^^^^^ help: try: `u64::from(handle)`

[oli-obk]

not a regression, just a bug ;) Const fn and constants have mostly the same rules, so we shouldn't suggest non-const stuff

[phansch]

New issue for this is #3656