Added new lint for `map_or(..., identity)` by teofr · Pull Request #16052 · rust-lang/rust-clippy

teofr · 2025-11-08T10:42:48Z

Introduce a new lint for mapping the identity function with map_or over Option and Result.

Lints:

fn foo(opt: Option<i32>, default: i32) -> i32 {
    opt.map_or(default, |o| o)
}

Into

fn foo(opt: Option<i32>, default: i32) -> i32 {
    opt.unwrap_or(default)
}

Fixes #15801

We had some discussions with @ada4a about naming on issue #15801 , a summary here.

There's a question about naming for this lint, there's already unnecessary_option_map_or_else and unnecessary_result_map_or_else, but I think having two lints doesn't make sense in this case.
unnecessary_map_or could be a reasonable name for this new lint, but it's already taken

changelog: [map_or_identity]: new lint

rustbot · 2025-11-28T07:12:01Z

r? @samueltardieu

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… identity)`

samueltardieu · 2026-01-08T20:04:28Z

+/// Note: `symbol` can only be `sym::Option` or `sym::Result`
+fn emit_lint(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, def_arg: &Expr<'_>, symbol: Symbol) {
+    debug_assert!(symbol == sym::Option || symbol == sym::Result);
+    let msg = format!("unused \"map closure\" when calling `{symbol}::map_or` value");


"map closure" is not really a well-known term. Why not something like "expression can be simplified"?

Change to "error: expression can be simplified using Result::unwrap_or()"

rustbot · 2026-01-08T20:07:49Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

ada4a · 2026-01-08T22:22:06Z

+    let mut applicability = Applicability::MachineApplicable;
+    let self_snippet = snippet_with_applicability(cx, recv.span, "_", &mut applicability);
+    let err_snippet = snippet_with_applicability(cx, def_arg.span, "..", &mut applicability);


Imo when there's a lot of heavy processing happening before span_lint_and_sugg, it's better to switch to span_lint_and_then and to do the processing in its closure.

Fwiw, this only brings performance improvements for allow-by-default lints -- if the lint is disabled, the closure of span_lint_and_then won't even run, whereas the version with span_lint_and_sugg will do the processing no matter what -- but still..

That makes sense, thanks. Changed it.

samueltardieu · 2026-01-18T09:47:45Z

@teofr Do you still intend to work on that? No pressure, but it's been two months since the most recent commit so I want to know whether to close this or not.

teofr · 2026-01-18T13:09:57Z

@samueltardieu Hey, yeah, I was on holidays for the past couple of weeks, I'm planning to address the comments this week.

teofr · 2026-01-20T09:17:53Z

@rustbot ready

samueltardieu · 2026-02-21T13:44:31Z

FCP thread created

samueltardieu

Strange, GitHub shows me this review as unsubmitted. Let's submit it.

View changes since this review

teofr · 2026-03-13T10:05:50Z

@rustbot ready

commit 3473e0a upstream. Starting with Rust 1.98.0 (expected 2026-08-20), Clippy is likely introducing a new lint `clippy::map_or_identity` [1][2], which currently triggers in a single case: warning: expression can be simplified using `Result::unwrap_or()` --> rust/kernel/cpufreq.rs:1326:60 | 1326 | PolicyCpu::from_cpu(cpu_id).map_or(0, |mut policy| T::get(&mut policy).map_or(0, |f| f)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_or_identity = note: `-W clippy::map-or-identity` implied by `-W clippy::all` = help: to override `-W clippy::all` add `#[allow(clippy::map_or_identity)]` help: consider using `unwrap_or` | 1326 - PolicyCpu::from_cpu(cpu_id).map_or(0, |mut policy| T::get(&mut policy).map_or(0, |f| f)) 1326 + PolicyCpu::from_cpu(cpu_id).map_or(0, |mut policy| T::get(&mut policy).unwrap_or(0)) | The suggestion is valid, thus clean it up. Cc: stable@vger.kernel.org # Needed in 6.18.y and later. Link: rust-lang/rust-clippy#15801 [1] Link: rust-lang/rust-clippy#16052 [2] Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com> Reviewed-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Link: https://patch.msgid.link/20260530095809.213611-1-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

rustbot added the needs-fcp PRs that add, remove, or rename lints and need an FCP label Nov 8, 2025

teofr force-pushed the issue_15801_2 branch from 6d20f77 to 295b304 Compare November 15, 2025 15:59

teofr force-pushed the issue_15801_2 branch from 295b304 to a096a23 Compare November 28, 2025 07:03

teofr marked this pull request as ready for review November 28, 2025 07:11

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Nov 28, 2025

rustbot assigned samueltardieu Nov 28, 2025

gauravagerwala added a commit to gauravagerwala/rust-clippy that referenced this pull request Dec 7, 2025

Update design for PR rust-lang#16052: Added new lint for `map_or(...,…

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… identity)`

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teofr force-pushed the issue_15801_2 branch from a096a23 to 886a088 Compare January 18, 2026 15:25

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Comment thread clippy_lints/src/methods/mod.rs Outdated

Comment thread clippy_lints/src/methods/map_or_identity.rs Outdated

Comment thread tests/ui/manual_ok_or.rs Outdated

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