rust-lang / rust-lang/rust-clippy
clippy::question_mark suggests code that's more confusing than before
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Description
Lint name: clippy::question_mark
I tried this code:
pub struct Message;
pub struct MessageUpdateEvent { content: Option<String> }
pub fn process_message_update(
user_msg_update: MessageUpdateEvent,
) -> Option<Message> {
// [some code]
// If message content wasn't touched, don't re-run command
if user_msg_update.content.is_none() {
return None;
}
// [more code]
Some(Message)
}
(for more context, see https://github.com/kangalioo/poise/blob/19bcc0afef2c77533a4e2f0a4aaffa4baea74f2a/src/prefix/track_edits.rs#L85-L92)
I expected to see this happen: no warning is emitted
Why: semantically, the ? operator is meant for propagating exceptional values which the current function doesn't want to deal with. The semantics in this code are different, so usage of ? would be confusing and make it harder to figure what is actually happening here
Instead, this happened: Clippy suggested to replace the check with user_msg_update.content.as_ref()?;
I am not sure how or if Clippy can detect intended semantics of if value.is_none() { return None; }. The best course of action may be to keep this lint as is, if it's not worth it to accommodate this small issue
Meta
Rust version (rustc -Vv):
rustc 1.55.0 (c8dfcfe04 2021-09-06)
binary: rustc
commit-hash: c8dfcfe046a7680554bf4eb612bad840e7631c4b
commit-date: 2021-09-06
host: x86_64-unknown-linux-gnu
release: 1.55.0
LLVM version: 12.0.1
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the clippy::question_mark lint and compare its suggestion against the linked track_edits.rs example at lines 85-92. Review the lint's existing behavior and tests, then determine whether this pattern should be excluded or documented; done means the example no longer receives a misleading suggestion, or the decision is covered by a regression test.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100