diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs index 3c3093e86..93b5d4e7e 100644 --- a/clippy_lints/src/methods/mod.rs +++ b/clippy_lints/src/methods/mod.rs @@ -1369,6 +1369,38 @@ declare_clippy_lint! { "using `.map(_).collect::()`, which can be replaced with `try_for_each`" } +declare_clippy_lint! { + /// **What it does:** Checks for `from_iter()` function calls that implements `FromIterator` + /// trait. + /// + /// **Why is this bad?** Makes code less readable especially in method chaining. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// + /// ```rust + /// use std::iter::FromIterator; + /// + /// let five_fives = std::iter::repeat(5).take(5); + /// + /// let v = Vec::from_iter(five_fives); + /// + /// assert_eq!(v, vec![5, 5, 5, 5, 5]); + /// ``` + /// Use instead: + /// ```rust + /// let five_fives = std::iter::repeat(5).take(5); + /// + /// let v: Vec = five_fives.collect(); + /// + /// assert_eq!(v, vec![5, 5, 5, 5, 5]); + /// ``` + pub FROM_ITER_INSTEAD_OF_COLLECT, + style, + "use `.collect()` instead of `::from_iter()`" +} + declare_lint_pass!(Methods => [ UNWRAP_USED, EXPECT_USED, @@ -1419,6 +1451,7 @@ declare_lint_pass!(Methods => [ OPTION_AS_REF_DEREF, UNNECESSARY_LAZY_EVALUATIONS, MAP_COLLECT_RESULT_UNIT, + FROM_ITER_INSTEAD_OF_COLLECT, ]); impl<'tcx> LateLintPass<'tcx> for Methods { @@ -1505,6 +1538,14 @@ impl<'tcx> LateLintPass<'tcx> for Methods { } match expr.kind { + hir::ExprKind::Call(ref func, ref args) => { + if let hir::ExprKind::Path(path) = &func.kind { + let path_segment = last_path_segment(path); + if path_segment.ident.name.as_str() == "from_iter" { + lint_from_iter(cx, expr, args); + } + } + }, hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args, _) => { lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args); lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args); @@ -3831,6 +3872,24 @@ fn lint_filetype_is_file(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir span_lint_and_help(cx, FILETYPE_IS_FILE, span, &lint_msg, None, &help_msg); } +fn lint_from_iter(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) { + let ty = cx.typeck_results().expr_ty(expr); + let id = get_trait_def_id(cx, &paths::FROM_ITERATOR_TRAIT).unwrap(); + + if implements_trait(cx, ty, id, &[]) { + // `expr` implements `FromIterator` trait + let iter_expr = snippet(cx, args[0].span, ".."); + span_lint_and_help( + cx, + FROM_ITER_INSTEAD_OF_COLLECT, + expr.span, + "use `.collect()` instead of `::from_iter()`", + None, + &format!("consider using `{}.collect()`", iter_expr), + ); + } +} + fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool { expected.constness == actual.constness && expected.unsafety == actual.unsafety diff --git a/clippy_lints/src/utils/paths.rs b/clippy_lints/src/utils/paths.rs index 736a531ed..3aade8ca8 100644 --- a/clippy_lints/src/utils/paths.rs +++ b/clippy_lints/src/utils/paths.rs @@ -44,6 +44,7 @@ pub const FN: [&str; 3] = ["core", "ops", "Fn"]; pub const FN_MUT: [&str; 3] = ["core", "ops", "FnMut"]; pub const FN_ONCE: [&str; 3] = ["core", "ops", "FnOnce"]; pub const FROM_FROM: [&str; 4] = ["core", "convert", "From", "from"]; +pub const FROM_ITERATOR_TRAIT: [&str; 3] = ["std", "iter", "FromIterator"]; pub const FROM_TRAIT: [&str; 3] = ["core", "convert", "From"]; pub const FUTURE_FROM_GENERATOR: [&str; 3] = ["core", "future", "from_generator"]; pub const HASH: [&str; 3] = ["core", "hash", "Hash"];