diff --git a/CHANGELOG.md b/CHANGELOG.md index 008a22906fc..6b63dbb7eff 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1803,6 +1803,7 @@ Released 2018-09-13 [`manual_unwrap_or`]: https://rust-lang.github.io/rust-clippy/master/index.html#manual_unwrap_or [`many_single_char_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#many_single_char_names [`map_clone`]: https://rust-lang.github.io/rust-clippy/master/index.html#map_clone +[`map_collect_result_unit`]: https://rust-lang.github.io/rust-clippy/master/index.html#map_collect_result_unit [`map_entry`]: https://rust-lang.github.io/rust-clippy/master/index.html#map_entry [`map_err_ignore`]: https://rust-lang.github.io/rust-clippy/master/index.html#map_err_ignore [`map_flatten`]: https://rust-lang.github.io/rust-clippy/master/index.html#map_flatten diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index eb4d0bdc6c9..97358e06c63 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -702,6 +702,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &methods::ITER_NTH_ZERO, &methods::ITER_SKIP_NEXT, &methods::MANUAL_SATURATING_ARITHMETIC, + &methods::MAP_COLLECT_RESULT_UNIT, &methods::MAP_FLATTEN, &methods::MAP_UNWRAP_OR, &methods::NEW_RET_NO_SELF, @@ -1428,6 +1429,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&methods::ITER_NTH_ZERO), LintId::of(&methods::ITER_SKIP_NEXT), LintId::of(&methods::MANUAL_SATURATING_ARITHMETIC), + LintId::of(&methods::MAP_COLLECT_RESULT_UNIT), LintId::of(&methods::NEW_RET_NO_SELF), LintId::of(&methods::OK_EXPECT), LintId::of(&methods::OPTION_AS_REF_DEREF), @@ -1623,6 +1625,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&methods::ITER_NTH_ZERO), LintId::of(&methods::ITER_SKIP_NEXT), LintId::of(&methods::MANUAL_SATURATING_ARITHMETIC), + LintId::of(&methods::MAP_COLLECT_RESULT_UNIT), LintId::of(&methods::NEW_RET_NO_SELF), LintId::of(&methods::OK_EXPECT), LintId::of(&methods::OPTION_MAP_OR_NONE), diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs index d250bfd71e9..aa893e794b8 100644 --- a/clippy_lints/src/methods/mod.rs +++ b/clippy_lints/src/methods/mod.rs @@ -1349,6 +1349,27 @@ declare_clippy_lint! { "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation" } +declare_clippy_lint! { + /// **What it does:** Checks for usage of `_.map(_).collect::()`. + /// + /// **Why is this bad?** Using `try_for_each` instead is more readable and idiomatic. + /// + /// **Known problems:** None + /// + /// **Example:** + /// + /// ```rust + /// (0..3).map(|t| Err(t)).collect::>(); + /// ``` + /// Use instead: + /// ```rust + /// (0..3).try_for_each(|t| Err(t)); + /// ``` + pub MAP_COLLECT_RESULT_UNIT, + style, + "using `.map(_).collect::()`, which can be replaced with `try_for_each`" +} + declare_lint_pass!(Methods => [ UNWRAP_USED, EXPECT_USED, @@ -1398,6 +1419,7 @@ declare_lint_pass!(Methods => [ FILETYPE_IS_FILE, OPTION_AS_REF_DEREF, UNNECESSARY_LAZY_EVALUATIONS, + MAP_COLLECT_RESULT_UNIT, ]); impl<'tcx> LateLintPass<'tcx> for Methods { @@ -1479,6 +1501,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods { ["unwrap_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "unwrap_or"), ["get_or_insert_with", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "get_or_insert"), ["ok_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "ok_or"), + ["collect", "map"] => lint_map_collect(cx, expr, arg_lists[1], arg_lists[0]), _ => {}, } @@ -3445,6 +3468,42 @@ fn lint_option_as_ref_deref<'tcx>( } } +fn lint_map_collect( + cx: &LateContext<'_>, + expr: &hir::Expr<'_>, + map_args: &[hir::Expr<'_>], + collect_args: &[hir::Expr<'_>], +) { + if_chain! { + // called on Iterator + if let [map_expr] = collect_args; + if match_trait_method(cx, map_expr, &paths::ITERATOR); + // return of collect `Result<(),_>` + let collect_ret_ty = cx.typeck_results().expr_ty(expr); + if is_type_diagnostic_item(cx, collect_ret_ty, sym!(result_type)); + if let ty::Adt(_, substs) = collect_ret_ty.kind(); + if let Some(result_t) = substs.types().next(); + if result_t.is_unit(); + // get parts for snippet + if let [iter, map_fn] = map_args; + then { + span_lint_and_sugg( + cx, + MAP_COLLECT_RESULT_UNIT, + expr.span, + "`.map().collect()` can be replaced with `.try_for_each()`", + "try this", + format!( + "{}.try_for_each({})", + snippet(cx, iter.span, ".."), + snippet(cx, map_fn.span, "..") + ), + Applicability::MachineApplicable, + ); + } + } +} + /// Given a `Result` type, return its error type (`E`). fn get_error_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option> { match ty.kind() { diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index 4ecbedd71ce..016bda77ef5 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -1229,6 +1229,13 @@ vec![ deprecation: None, module: "map_clone", }, + Lint { + name: "map_collect_result_unit", + group: "style", + desc: "using `.map(_).collect::()`, which can be replaced with `try_for_each`", + deprecation: None, + module: "methods", + }, Lint { name: "map_entry", group: "perf", diff --git a/tests/ui/map_collect_result_unit.fixed b/tests/ui/map_collect_result_unit.fixed new file mode 100644 index 00000000000..e66c9cc2420 --- /dev/null +++ b/tests/ui/map_collect_result_unit.fixed @@ -0,0 +1,16 @@ +// run-rustfix +#![warn(clippy::map_collect_result_unit)] + +fn main() { + { + let _ = (0..3).try_for_each(|t| Err(t + 1)); + let _: Result<(), _> = (0..3).try_for_each(|t| Err(t + 1)); + + let _ = (0..3).try_for_each(|t| Err(t + 1)); + } +} + +fn _ignore() { + let _ = (0..3).map(|t| Err(t + 1)).collect::, _>>(); + let _ = (0..3).map(|t| Err(t + 1)).collect::>>(); +} diff --git a/tests/ui/map_collect_result_unit.rs b/tests/ui/map_collect_result_unit.rs new file mode 100644 index 00000000000..6f08f4c3c53 --- /dev/null +++ b/tests/ui/map_collect_result_unit.rs @@ -0,0 +1,16 @@ +// run-rustfix +#![warn(clippy::map_collect_result_unit)] + +fn main() { + { + let _ = (0..3).map(|t| Err(t + 1)).collect::>(); + let _: Result<(), _> = (0..3).map(|t| Err(t + 1)).collect(); + + let _ = (0..3).try_for_each(|t| Err(t + 1)); + } +} + +fn _ignore() { + let _ = (0..3).map(|t| Err(t + 1)).collect::, _>>(); + let _ = (0..3).map(|t| Err(t + 1)).collect::>>(); +} diff --git a/tests/ui/map_collect_result_unit.stderr b/tests/ui/map_collect_result_unit.stderr new file mode 100644 index 00000000000..8b06e13baa6 --- /dev/null +++ b/tests/ui/map_collect_result_unit.stderr @@ -0,0 +1,16 @@ +error: `.map().collect()` can be replaced with `.try_for_each()` + --> $DIR/map_collect_result_unit.rs:6:17 + | +LL | let _ = (0..3).map(|t| Err(t + 1)).collect::>(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `(0..3).try_for_each(|t| Err(t + 1))` + | + = note: `-D clippy::map-collect-result-unit` implied by `-D warnings` + +error: `.map().collect()` can be replaced with `.try_for_each()` + --> $DIR/map_collect_result_unit.rs:7:32 + | +LL | let _: Result<(), _> = (0..3).map(|t| Err(t + 1)).collect(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `(0..3).try_for_each(|t| Err(t + 1))` + +error: aborting due to 2 previous errors +