Warning about needless collect but suggestion does not compile

Clippy warns about a needless collect, but the suggested code does not compile.

I have something similar to this code (condensed):

let keys = map.keys().copied().collect::<Vec<_>>();

for key in keys.into_iter() {
    // since .keys() has been copied and collected, I'm not
    // borrowing the map anymore and I can mutate the map here.
    map.remove(key);
}

Suggestion from clippy:

warning: avoid using `collect()` when not needed
  --> src/main.rs:18:5
   |
18 | /     let keys = map.keys().copied().collect::<Vec<_>>();
19 | |
20 | |     for key in keys.into_iter() {
   | |_______________^
   |
   = note: `#[warn(clippy::needless_collect)]` on by default
help: Use the original Iterator instead of collecting it and then producing a new one
   |
18 |     
19 | 
20 |     for key in map.keys().copied() {
   |

This suggestion will not compile because maps.keys().copied() borrows the map.

Full code example: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=711425060fb8ac794003067454010a69

Expectation: the warning does not appear because removing the .collect() would break the code.

Instead, this happened: the needless_collect warning triggered. Additionally, it's not possible to mute this warning for a specific line, so I resorted to adding #![allow(clippy::needless_collect)] to the entire file.

Meta

• cargo +nightly clippy -V: clippy 0.0.212 (1c389ffe 2020-11-24) (I use the nightly clippy to get more warnings)
• rustc -Vv:

rustc 1.48.0 (7eac88abb 2020-11-16)
binary: rustc
commit-hash: 7eac88abb2e57e752f3302f02be5f3ce3d7adfb4
commit-date: 2020-11-16
host: x86_64-apple-darwin
release: 1.48.0
LLVM version: 11.0

Reproduce the needless_collect warning with the condensed example in src/main.rs or the linked Rust playground, focusing on the map mutation after collecting keys. Trace the needless_collect lint entry point and its suggested replacement; done means the lint no longer suggests removing collect when that change causes a borrow-checking error, with a regression test covering the example.