collapsible_match merges conditions when nested condition consumes variable

[WhyNotHugo]

Summary

In a match, one of my arms has an if inside which consumes a variable. collapsible_match suggests collapsing the if into the match's condition, and even performs the fix, but the fix does not compile, since the if consumes a variable which is referrenced in other arms.

Lint Name

collapsible_match

Reproducer

I tried this code:

    for item in <(pem::SectionKind, Vec<u8>) as PemObject>::pem_file_iter(path)? {
        let (kind, der) = item?;
        match kind {
            pem::SectionKind::Certificate => {
                certs.push(CertificateDer::from(der));
            }
            pem::SectionKind::EcPrivateKey => {
                if raw_key.replace(PrivateKeyDer::Sec1(der.into())).is_some() {
                    bail!("multiple keys found in {}", path.to_string_lossy());
                }
            }
            pem::SectionKind::PrivateKey => {
                if raw_key.replace(PrivateKeyDer::Pkcs8(der.into())).is_some() {
                    bail!("multiple keys found in {}", path.to_string_lossy());
                }
            }
            pem::SectionKind::RsaPrivateKey => {
                if raw_key.replace(PrivateKeyDer::Pkcs1(der.into())).is_some() {
                    bail!("multiple keys found in {}", path.to_string_lossy());
                }
            }
            _ => {}
        }
    }

I saw this happen:

> cargo clippy --allow-dirty --fix
   Compiling pimsync v0.0.0 (/home/hugo/src/git.sr.ht/~whynothugo/pimsync)
warning: failed to automatically apply fixes suggested by rustc to crate `pimsync`

after fixes were automatically applied the compiler reported errors within these files:

  * src/tls.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust-clippy/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0382]: use of moved value: `der`
   --> src/tls.rs:183:57
    |
173 |         let (kind, der) = item?;
    |                    ---
    |                    |
    |                    this reinitialization might get skipped
    |                    move occurs because `der` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait
...
179 |                 if raw_key.replace(PrivateKeyDer::Sec1(der.into())).is_some() => {
    |                                                            ------ `der` moved due to this method call
...
183 |                 if raw_key.replace(PrivateKeyDer::Pkcs8(der.into())).is_some() => {
    |                                                         ^^^ value used here after move
    |
note: `std::convert::Into::into` takes ownership of the receiver `self`, which moves `der`
   --> /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/convert/mod.rs:455:12
help: you can `clone` the value and consume it, but this might not be your desired behavior
    |
179 |                 if raw_key.replace(PrivateKeyDer::Sec1(der.clone().into())).is_some() => {
    |                                                           ++++++++

error[E0382]: use of moved value: `der`
   --> src/tls.rs:187:57
    |
173 |         let (kind, der) = item?;
    |                    ---
    |                    |
    |                    this reinitialization might get skipped
    |                    move occurs because `der` has type `std::vec::Vec<u8>`, which does not implement the `Copy` trait
...
179 |                 if raw_key.replace(PrivateKeyDer::Sec1(der.into())).is_some() => {
    |                                                            ------ `der` moved due to this method call
...
183 |                 if raw_key.replace(PrivateKeyDer::Pkcs8(der.into())).is_some() => {
    |                                                             ------ `der` moved due to this method call
...
187 |                 if raw_key.replace(PrivateKeyDer::Pkcs1(der.into())).is_some() => {
    |                                                         ^^^ value used here after move
    |
help: you can `clone` the value and consume it, but this might not be your desired behavior
    |
183 |                 if raw_key.replace(PrivateKeyDer::Pkcs8(der.clone().into())).is_some() => {
    |                                                            ++++++++
help: you can `clone` the value and consume it, but this might not be your desired behavior
    |
179 |                 if raw_key.replace(PrivateKeyDer::Sec1(der.clone().into())).is_some() => {
    |                                                           ++++++++

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0382`.
Original diagnostics will follow.

warning: this `if` can be collapsed into the outer `match`
   --> src/tls.rs:179:17
    |
179 | /                 if raw_key.replace(PrivateKeyDer::Sec1(der.into())).is_some() {
180 | |                     bail!("multiple keys found in {}", path.to_string_lossy());
181 | |                 }
    | |_________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.95.0/index.html#collapsible_match
    = note: `#[warn(clippy::collapsible_match)]` on by default
help: collapse nested if block
    |
178 ~             pem::SectionKind::EcPrivateKey
179 ~                 if raw_key.replace(PrivateKeyDer::Sec1(der.into())).is_some() => {
180 |                     bail!("multiple keys found in {}", path.to_string_lossy());
181 ~                 }
    |

warning: this `if` can be collapsed into the outer `match`
   --> src/tls.rs:184:17
    |
184 | /                 if raw_key.replace(PrivateKeyDer::Pkcs8(der.into())).is_some() {
185 | |                     bail!("multiple keys found in {}", path.to_string_lossy());
186 | |                 }
    | |_________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.95.0/index.html#collapsible_match
help: collapse nested if block
    |
183 ~             pem::SectionKind::PrivateKey
184 ~                 if raw_key.replace(PrivateKeyDer::Pkcs8(der.into())).is_some() => {
185 |                     bail!("multiple keys found in {}", path.to_string_lossy());
186 ~                 }
    |

warning: this `if` can be collapsed into the outer `match`
   --> src/tls.rs:189:17
    |
189 | /                 if raw_key.replace(PrivateKeyDer::Pkcs1(der.into())).is_some() {
190 | |                     bail!("multiple keys found in {}", path.to_string_lossy());
191 | |                 }
    | |_________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.95.0/index.html#collapsible_match
help: collapse nested if block
    |
188 ~             pem::SectionKind::RsaPrivateKey
189 ~                 if raw_key.replace(PrivateKeyDer::Pkcs1(der.into())).is_some() => {
190 |                     bail!("multiple keys found in {}", path.to_string_lossy());
191 ~                 }
    |

warning: `pimsync` (bin "pimsync") generated 3 warnings (run `cargo clippy --fix --bin "pimsync" -p pimsync -- --no-deps` to apply 3 suggestions)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.10s

I expected to see this happen:

No warning; these conditions cannot be collapsed. This is a false positive, and the "fix" is invalid.

Version

rustc 1.95.0 (59807616e 2026-04-14) (Alpine Linux Rust 1.95.0-r0)
binary: rustc
commit-hash: 59807616e1fa2540724bfbac14d7976d7e4a3860
commit-date: 2026-04-14
host: x86_64-alpine-linux-musl
release: 1.95.0
LLVM version: 22.1.3

Additional Labels

Vaguely similar to #16903, although that issue is about mutable borrows and this one is about the variable being consumed.

[WhyNotHugo]

The exact code is from repository https://git.sr.ht/~whynothugo/pimsync/, commit 90d240b03ac72f6b1a85f05a6f348901697788ca, file src/tls.rs.

[Kokoro2336]

@rustbot claim