const functions should not trigger or_fun_call

[Sciencentistguy]

Lint name: or_fun_call

I tried this code:

let x = None;
let s: &str = "hello world";
s.unwrap_or(s.len());

I expected to see this happen: As str::len is a const function, it is inlined as a usize. So the suggestion to use .unwrap_or_else() introduces more overhead than is needed.

Instead, this happened: The lint is triggered

Meta

• cargo clippy -V: clippy 0.1.52 (f5d8117 2021-03-16)
• rustc -Vv:

rustc 1.52.0-nightly (f5d8117c3 2021-03-16)
binary: rustc
commit-hash: f5d8117c338a788bd24abec733fd143dfceb25a0
commit-date: 2021-03-16
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 12.0.0

[camsteffen]

We cannot simply ignore const functions since they are not guaranteed to be evaluated at compile time. See #1527. However we can ignore str::len since we also ignore slice::len.