diff --git a/CHANGELOG.md b/CHANGELOG.md index 664a7e766304..3e68b46cb0f6 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -5493,6 +5493,7 @@ Released 2018-09-13 [`doc_markdown`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_markdown [`doc_nested_refdefs`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_nested_refdefs [`double_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_comparisons +[`double_ended_iterator_last`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_ended_iterator_last [`double_must_use`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_must_use [`double_neg`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_neg [`double_parens`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_parens diff --git a/clippy_lints/src/attrs/mixed_attributes_style.rs b/clippy_lints/src/attrs/mixed_attributes_style.rs index 32c28c09c360..8c91c65eaf76 100644 --- a/clippy_lints/src/attrs/mixed_attributes_style.rs +++ b/clippy_lints/src/attrs/mixed_attributes_style.rs @@ -66,7 +66,7 @@ pub(super) fn check(cx: &EarlyContext<'_>, item_span: Span, attrs: &[Attribute]) fn lint_mixed_attrs(cx: &EarlyContext<'_>, attrs: &[Attribute]) { let mut attrs_iter = attrs.iter().filter(|attr| !attr.span.from_expansion()); - let span = if let (Some(first), Some(last)) = (attrs_iter.next(), attrs_iter.last()) { + let span = if let (Some(first), Some(last)) = (attrs_iter.next(), attrs_iter.next_back()) { first.span.with_hi(last.span.hi()) } else { return; diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs index 7451fb909ef8..3ff10d850f82 100644 --- a/clippy_lints/src/declared_lints.rs +++ b/clippy_lints/src/declared_lints.rs @@ -372,6 +372,7 @@ pub static LINTS: &[&crate::LintInfo] = &[ crate::methods::CLONE_ON_REF_PTR_INFO, crate::methods::COLLAPSIBLE_STR_REPLACE_INFO, crate::methods::CONST_IS_EMPTY_INFO, + crate::methods::DOUBLE_ENDED_ITERATOR_LAST_INFO, crate::methods::DRAIN_COLLECT_INFO, crate::methods::ERR_EXPECT_INFO, crate::methods::EXPECT_FUN_CALL_INFO, diff --git a/clippy_lints/src/methods/double_ended_iterator_last.rs b/clippy_lints/src/methods/double_ended_iterator_last.rs new file mode 100644 index 000000000000..208172980c9f --- /dev/null +++ b/clippy_lints/src/methods/double_ended_iterator_last.rs @@ -0,0 +1,41 @@ +use clippy_utils::diagnostics::span_lint_and_sugg; +use clippy_utils::is_trait_method; +use clippy_utils::ty::implements_trait; +use rustc_errors::Applicability; +use rustc_hir::Expr; +use rustc_lint::LateContext; +use rustc_middle::ty::Instance; +use rustc_span::{Span, sym}; + +use super::DOUBLE_ENDED_ITERATOR_LAST; + +pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, self_expr: &'_ Expr<'_>, call_span: Span) { + let typeck = cx.typeck_results(); + + // if the "last" method is that of Iterator + if is_trait_method(cx, expr, sym::Iterator) + // if self implements DoubleEndedIterator + && let Some(deiter_id) = cx.tcx.get_diagnostic_item(sym::DoubleEndedIterator) + && let self_type = cx.typeck_results().expr_ty(self_expr) + && implements_trait(cx, self_type.peel_refs(), deiter_id, &[]) + // resolve the method definition + && let id = typeck.type_dependent_def_id(expr.hir_id).unwrap() + && let args = typeck.node_args(expr.hir_id) + && let Ok(Some(fn_def)) = Instance::try_resolve(cx.tcx, cx.typing_env(), id, args) + // find the provided definition of Iterator::last + && let Some(item) = cx.tcx.get_diagnostic_item(sym::Iterator) + && let Some(last_def) = cx.tcx.provided_trait_methods(item).find(|m| m.name.as_str() == "last") + // if the resolved method is the same as the provided definition + && fn_def.def_id() == last_def.def_id + { + span_lint_and_sugg( + cx, + DOUBLE_ENDED_ITERATOR_LAST, + call_span, + "called `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator", + "try", + "next_back()".to_string(), + Applicability::MachineApplicable, + ); + } +} diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs index 810287fa5416..51351f6b7cd1 100644 --- a/clippy_lints/src/methods/mod.rs +++ b/clippy_lints/src/methods/mod.rs @@ -14,6 +14,7 @@ mod clone_on_copy; mod clone_on_ref_ptr; mod cloned_instead_of_copied; mod collapsible_str_replace; +mod double_ended_iterator_last; mod drain_collect; mod err_expect; mod expect_fun_call; @@ -4284,6 +4285,32 @@ declare_clippy_lint! { "map of a trivial closure (not dependent on parameter) over a range" } +declare_clippy_lint! { + /// ### What it does + /// + /// Checks for `Iterator::last` being called on a `DoubleEndedIterator`, which can be replaced + /// with `DoubleEndedIterator::next_back`. + /// + /// ### Why is this bad? + /// + /// `Iterator::last` is implemented by consuming the iterator, which is unnecessary if + /// the iterator is a `DoubleEndedIterator`. Since Rust traits do not allow specialization, + /// `Iterator::last` cannot be optimized for `DoubleEndedIterator`. + /// + /// ### Example + /// ```no_run + /// let last_arg = "echo hello world".split(' ').last(); + /// ``` + /// Use instead: + /// ```no_run + /// let last_arg = "echo hello world".split(' ').next_back(); + /// ``` + #[clippy::version = "1.85.0"] + pub DOUBLE_ENDED_ITERATOR_LAST, + perf, + "using `Iterator::last` on a `DoubleEndedIterator`" +} + pub struct Methods { avoid_breaking_exported_api: bool, msrv: Msrv, @@ -4449,6 +4476,7 @@ impl_lint_pass!(Methods => [ MAP_ALL_ANY_IDENTITY, MAP_WITH_UNUSED_ARGUMENT_OVER_RANGES, UNNECESSARY_MAP_OR, + DOUBLE_ENDED_ITERATOR_LAST, ]); /// Extracts a method call name, args, and `Span` of the method name. @@ -4931,6 +4959,7 @@ impl Methods { false, ); } + double_ended_iterator_last::check(cx, expr, recv, call_span); }, ("len", []) => { if let Some(("as_bytes", prev_recv, [], _, _)) = method_call(recv) { diff --git a/clippy_utils/src/msrvs.rs b/clippy_utils/src/msrvs.rs index 98bcedecccc6..2169a5fdd63b 100644 --- a/clippy_utils/src/msrvs.rs +++ b/clippy_utils/src/msrvs.rs @@ -130,7 +130,7 @@ impl Msrv { let mut msrv_attrs = attrs.iter().filter(|attr| attr.path_matches(&[sym::clippy, sym_msrv])); if let Some(msrv_attr) = msrv_attrs.next() { - if let Some(duplicate) = msrv_attrs.last() { + if let Some(duplicate) = msrv_attrs.next_back() { sess.dcx() .struct_span_err(duplicate.span(), "`clippy::msrv` is defined multiple times") .with_span_note(msrv_attr.span(), "first definition found here") diff --git a/tests/ui/double_ended_iterator_last.fixed b/tests/ui/double_ended_iterator_last.fixed new file mode 100644 index 000000000000..06c48e337537 --- /dev/null +++ b/tests/ui/double_ended_iterator_last.fixed @@ -0,0 +1,53 @@ +#![warn(clippy::double_ended_iterator_last)] + +// Typical case +pub fn last_arg(s: &str) -> Option<&str> { + s.split(' ').next_back() +} + +fn main() { + // General case + struct DeIterator; + impl Iterator for DeIterator { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + } + impl DoubleEndedIterator for DeIterator { + fn next_back(&mut self) -> Option { + Some(()) + } + } + let _ = DeIterator.next_back(); + // Should not apply to other methods of Iterator + let _ = DeIterator.count(); + + // Should not apply to simple iterators + struct SimpleIterator; + impl Iterator for SimpleIterator { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + } + let _ = SimpleIterator.last(); + + // Should not apply to custom implementations of last() + struct CustomLast; + impl Iterator for CustomLast { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + fn last(self) -> Option { + Some(()) + } + } + impl DoubleEndedIterator for CustomLast { + fn next_back(&mut self) -> Option { + Some(()) + } + } + let _ = CustomLast.last(); +} diff --git a/tests/ui/double_ended_iterator_last.rs b/tests/ui/double_ended_iterator_last.rs new file mode 100644 index 000000000000..9c13b496d117 --- /dev/null +++ b/tests/ui/double_ended_iterator_last.rs @@ -0,0 +1,53 @@ +#![warn(clippy::double_ended_iterator_last)] + +// Typical case +pub fn last_arg(s: &str) -> Option<&str> { + s.split(' ').last() +} + +fn main() { + // General case + struct DeIterator; + impl Iterator for DeIterator { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + } + impl DoubleEndedIterator for DeIterator { + fn next_back(&mut self) -> Option { + Some(()) + } + } + let _ = DeIterator.last(); + // Should not apply to other methods of Iterator + let _ = DeIterator.count(); + + // Should not apply to simple iterators + struct SimpleIterator; + impl Iterator for SimpleIterator { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + } + let _ = SimpleIterator.last(); + + // Should not apply to custom implementations of last() + struct CustomLast; + impl Iterator for CustomLast { + type Item = (); + fn next(&mut self) -> Option { + Some(()) + } + fn last(self) -> Option { + Some(()) + } + } + impl DoubleEndedIterator for CustomLast { + fn next_back(&mut self) -> Option { + Some(()) + } + } + let _ = CustomLast.last(); +} diff --git a/tests/ui/double_ended_iterator_last.stderr b/tests/ui/double_ended_iterator_last.stderr new file mode 100644 index 000000000000..b795c18a736e --- /dev/null +++ b/tests/ui/double_ended_iterator_last.stderr @@ -0,0 +1,17 @@ +error: called `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator + --> tests/ui/double_ended_iterator_last.rs:5:18 + | +LL | s.split(' ').last() + | ^^^^^^ help: try: `next_back()` + | + = note: `-D clippy::double-ended-iterator-last` implied by `-D warnings` + = help: to override `-D warnings` add `#[allow(clippy::double_ended_iterator_last)]` + +error: called `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator + --> tests/ui/double_ended_iterator_last.rs:22:24 + | +LL | let _ = DeIterator.last(); + | ^^^^^^ help: try: `next_back()` + +error: aborting due to 2 previous errors + diff --git a/tests/ui/infinite_iter.rs b/tests/ui/infinite_iter.rs index da95ba04b821..178e300ff5bf 100644 --- a/tests/ui/infinite_iter.rs +++ b/tests/ui/infinite_iter.rs @@ -1,4 +1,4 @@ -#![allow(clippy::uninlined_format_args)] +#![allow(clippy::uninlined_format_args, clippy::double_ended_iterator_last)] use std::iter::repeat; fn square_is_lower_64(x: &u32) -> bool { diff --git a/tests/ui/iter_overeager_cloned.fixed b/tests/ui/iter_overeager_cloned.fixed index 7d8a584b0224..d7d3d299349e 100644 --- a/tests/ui/iter_overeager_cloned.fixed +++ b/tests/ui/iter_overeager_cloned.fixed @@ -1,5 +1,10 @@ #![warn(clippy::iter_overeager_cloned, clippy::redundant_clone, clippy::filter_next)] -#![allow(dead_code, clippy::let_unit_value, clippy::useless_vec)] +#![allow( + dead_code, + clippy::let_unit_value, + clippy::useless_vec, + clippy::double_ended_iterator_last +)] fn main() { let vec = vec!["1".to_string(), "2".to_string(), "3".to_string()]; diff --git a/tests/ui/iter_overeager_cloned.rs b/tests/ui/iter_overeager_cloned.rs index 58c374ab8cd1..45e1349febd0 100644 --- a/tests/ui/iter_overeager_cloned.rs +++ b/tests/ui/iter_overeager_cloned.rs @@ -1,5 +1,10 @@ #![warn(clippy::iter_overeager_cloned, clippy::redundant_clone, clippy::filter_next)] -#![allow(dead_code, clippy::let_unit_value, clippy::useless_vec)] +#![allow( + dead_code, + clippy::let_unit_value, + clippy::useless_vec, + clippy::double_ended_iterator_last +)] fn main() { let vec = vec!["1".to_string(), "2".to_string(), "3".to_string()]; diff --git a/tests/ui/iter_overeager_cloned.stderr b/tests/ui/iter_overeager_cloned.stderr index 7a822a79494b..e6680266f107 100644 --- a/tests/ui/iter_overeager_cloned.stderr +++ b/tests/ui/iter_overeager_cloned.stderr @@ -1,5 +1,5 @@ error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:7:29 + --> tests/ui/iter_overeager_cloned.rs:12:29 | LL | let _: Option = vec.iter().cloned().last(); | ^^^^^^^^^^---------------- @@ -10,7 +10,7 @@ LL | let _: Option = vec.iter().cloned().last(); = help: to override `-D warnings` add `#[allow(clippy::iter_overeager_cloned)]` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:9:29 + --> tests/ui/iter_overeager_cloned.rs:14:29 | LL | let _: Option = vec.iter().chain(vec.iter()).cloned().next(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^---------------- @@ -18,7 +18,7 @@ LL | let _: Option = vec.iter().chain(vec.iter()).cloned().next(); | help: try: `.next().cloned()` error: unneeded cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:11:20 + --> tests/ui/iter_overeager_cloned.rs:16:20 | LL | let _: usize = vec.iter().filter(|x| x == &"2").cloned().count(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^----------------- @@ -29,7 +29,7 @@ LL | let _: usize = vec.iter().filter(|x| x == &"2").cloned().count(); = help: to override `-D warnings` add `#[allow(clippy::redundant_clone)]` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:13:21 + --> tests/ui/iter_overeager_cloned.rs:18:21 | LL | let _: Vec<_> = vec.iter().cloned().take(2).collect(); | ^^^^^^^^^^----------------- @@ -37,7 +37,7 @@ LL | let _: Vec<_> = vec.iter().cloned().take(2).collect(); | help: try: `.take(2).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:15:21 + --> tests/ui/iter_overeager_cloned.rs:20:21 | LL | let _: Vec<_> = vec.iter().cloned().skip(2).collect(); | ^^^^^^^^^^----------------- @@ -45,7 +45,7 @@ LL | let _: Vec<_> = vec.iter().cloned().skip(2).collect(); | help: try: `.skip(2).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:17:13 + --> tests/ui/iter_overeager_cloned.rs:22:13 | LL | let _ = vec.iter().filter(|x| x == &"2").cloned().nth(2); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---------------- @@ -53,7 +53,7 @@ LL | let _ = vec.iter().filter(|x| x == &"2").cloned().nth(2); | help: try: `.nth(2).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:19:13 + --> tests/ui/iter_overeager_cloned.rs:24:13 | LL | let _ = [Some(Some("str".to_string())), Some(Some("str".to_string()))] | _____________^ @@ -69,7 +69,7 @@ LL ~ .flatten().cloned(); | error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:24:13 + --> tests/ui/iter_overeager_cloned.rs:29:13 | LL | let _ = vec.iter().cloned().filter(|x| x.starts_with('2')); | ^^^^^^^^^^---------------------------------------- @@ -77,7 +77,7 @@ LL | let _ = vec.iter().cloned().filter(|x| x.starts_with('2')); | help: try: `.filter(|&x| x.starts_with('2')).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:26:13 + --> tests/ui/iter_overeager_cloned.rs:31:13 | LL | let _ = vec.iter().cloned().find(|x| x == "2"); | ^^^^^^^^^^---------------------------- @@ -85,7 +85,7 @@ LL | let _ = vec.iter().cloned().find(|x| x == "2"); | help: try: `.find(|&x| x == "2").cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:30:17 + --> tests/ui/iter_overeager_cloned.rs:35:17 | LL | let _ = vec.iter().cloned().filter(f); | ^^^^^^^^^^------------------- @@ -93,7 +93,7 @@ LL | let _ = vec.iter().cloned().filter(f); | help: try: `.filter(|&x| f(x)).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:31:17 + --> tests/ui/iter_overeager_cloned.rs:36:17 | LL | let _ = vec.iter().cloned().find(f); | ^^^^^^^^^^----------------- @@ -101,7 +101,7 @@ LL | let _ = vec.iter().cloned().find(f); | help: try: `.find(|&x| f(x)).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:37:17 + --> tests/ui/iter_overeager_cloned.rs:42:17 | LL | let _ = vec.iter().cloned().filter(f); | ^^^^^^^^^^------------------- @@ -109,7 +109,7 @@ LL | let _ = vec.iter().cloned().filter(f); | help: try: `.filter(|&x| f(x)).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:38:17 + --> tests/ui/iter_overeager_cloned.rs:43:17 | LL | let _ = vec.iter().cloned().find(f); | ^^^^^^^^^^----------------- @@ -117,7 +117,7 @@ LL | let _ = vec.iter().cloned().find(f); | help: try: `.find(|&x| f(x)).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:45:9 + --> tests/ui/iter_overeager_cloned.rs:50:9 | LL | iter.cloned().filter(move |(&a, b)| a == 1 && b == &target) | ^^^^------------------------------------------------------- @@ -125,7 +125,7 @@ LL | iter.cloned().filter(move |(&a, b)| a == 1 && b == &target) | help: try: `.filter(move |&(&a, b)| a == 1 && b == &target).cloned()` error: unnecessarily eager cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:56:13 + --> tests/ui/iter_overeager_cloned.rs:61:13 | LL | iter.cloned().filter(move |S { a, b }| **a == 1 && b == &target) | ^^^^------------------------------------------------------------ @@ -133,7 +133,7 @@ LL | iter.cloned().filter(move |S { a, b }| **a == 1 && b == &target | help: try: `.filter(move |&S { a, b }| **a == 1 && b == &target).cloned()` error: unneeded cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:60:13 + --> tests/ui/iter_overeager_cloned.rs:65:13 | LL | let _ = vec.iter().cloned().map(|x| x.len()); | ^^^^^^^^^^-------------------------- @@ -141,7 +141,7 @@ LL | let _ = vec.iter().cloned().map(|x| x.len()); | help: try: `.map(|x| x.len())` error: unneeded cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:65:13 + --> tests/ui/iter_overeager_cloned.rs:70:13 | LL | let _ = vec.iter().cloned().for_each(|x| assert!(!x.is_empty())); | ^^^^^^^^^^---------------------------------------------- @@ -149,7 +149,7 @@ LL | let _ = vec.iter().cloned().for_each(|x| assert!(!x.is_empty())); | help: try: `.for_each(|x| assert!(!x.is_empty()))` error: unneeded cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:67:13 + --> tests/ui/iter_overeager_cloned.rs:72:13 | LL | let _ = vec.iter().cloned().all(|x| x.len() == 1); | ^^^^^^^^^^------------------------------- @@ -157,7 +157,7 @@ LL | let _ = vec.iter().cloned().all(|x| x.len() == 1); | help: try: `.all(|x| x.len() == 1)` error: unneeded cloning of iterator items - --> tests/ui/iter_overeager_cloned.rs:69:13 + --> tests/ui/iter_overeager_cloned.rs:74:13 | LL | let _ = vec.iter().cloned().any(|x| x.len() == 1); | ^^^^^^^^^^------------------------------- diff --git a/tests/ui/starts_ends_with.fixed b/tests/ui/starts_ends_with.fixed index 4a66ca7ec91a..252b6e5a98c0 100644 --- a/tests/ui/starts_ends_with.fixed +++ b/tests/ui/starts_ends_with.fixed @@ -1,4 +1,4 @@ -#![allow(clippy::needless_if, dead_code, unused_must_use)] +#![allow(clippy::needless_if, dead_code, unused_must_use, clippy::double_ended_iterator_last)] fn main() {} diff --git a/tests/ui/starts_ends_with.rs b/tests/ui/starts_ends_with.rs index 16a68e02d66d..6c5655f31782 100644 --- a/tests/ui/starts_ends_with.rs +++ b/tests/ui/starts_ends_with.rs @@ -1,4 +1,4 @@ -#![allow(clippy::needless_if, dead_code, unused_must_use)] +#![allow(clippy::needless_if, dead_code, unused_must_use, clippy::double_ended_iterator_last)] fn main() {}