diff --git a/CHANGELOG.md b/CHANGELOG.md index 23f4f97ee07..735ac59758a 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -4582,6 +4582,7 @@ Released 2018-09-13 [`debug_assert_with_mut_call`]: https://rust-lang.github.io/rust-clippy/master/index.html#debug_assert_with_mut_call [`decimal_literal_representation`]: https://rust-lang.github.io/rust-clippy/master/index.html#decimal_literal_representation [`declare_interior_mutable_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#declare_interior_mutable_const +[`default_constructed_unit_struct`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_constructed_unit_struct [`default_instead_of_iter_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_instead_of_iter_empty [`default_numeric_fallback`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_numeric_fallback [`default_trait_access`]: https://rust-lang.github.io/rust-clippy/master/index.html#default_trait_access diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs index 4aebd0b7d01..bf30f5b52f7 100644 --- a/clippy_lints/src/declared_lints.rs +++ b/clippy_lints/src/declared_lints.rs @@ -105,6 +105,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[ crate::dbg_macro::DBG_MACRO_INFO, crate::default::DEFAULT_TRAIT_ACCESS_INFO, crate::default::FIELD_REASSIGN_WITH_DEFAULT_INFO, + crate::default_constructed_unit_struct::DEFAULT_CONSTRUCTED_UNIT_STRUCT_INFO, crate::default_instead_of_iter_empty::DEFAULT_INSTEAD_OF_ITER_EMPTY_INFO, crate::default_numeric_fallback::DEFAULT_NUMERIC_FALLBACK_INFO, crate::default_union_representation::DEFAULT_UNION_REPRESENTATION_INFO, diff --git a/clippy_lints/src/default_constructed_unit_struct.rs b/clippy_lints/src/default_constructed_unit_struct.rs new file mode 100644 index 00000000000..a04f7b9d9a9 --- /dev/null +++ b/clippy_lints/src/default_constructed_unit_struct.rs @@ -0,0 +1,66 @@ +use clippy_utils::{diagnostics::span_lint_and_sugg, is_from_proc_macro, match_def_path, paths}; +use hir::{def::Res, ExprKind}; +use rustc_errors::Applicability; +use rustc_hir as hir; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_middle::ty; +use rustc_session::{declare_lint_pass, declare_tool_lint}; + +declare_clippy_lint! { + /// ### What it does + /// Check for construction on unit struct using `default`. + /// + /// ### Why is this bad? + /// This adds code complexity and an unnecessary function call. + /// + /// ### Example + /// ```rust + /// #[derive(Default)] + /// struct S { + /// _marker: PhantomData + /// } + /// + /// let _: S = S { + /// _marker: PhantomData::default() + /// }; + /// ``` + /// Use instead: + /// ```rust + /// let _: S = Something { + /// _marker: PhantomData + /// } + /// ``` + #[clippy::version = "1.71.0"] + pub DEFAULT_CONSTRUCTED_UNIT_STRUCT, + complexity, + "unit structs can be contructed without calling `default`" +} +declare_lint_pass!(DefaultConstructedUnitStruct => [DEFAULT_CONSTRUCTED_UNIT_STRUCT]); + +impl LateLintPass<'_> for DefaultConstructedUnitStruct { + fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) { + if_chain!( + // make sure we have a call to `Default::default` + if let hir::ExprKind::Call(fn_expr, &[]) = expr.kind; + if let ExprKind::Path(ref qpath) = fn_expr.kind; + if let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id); + if match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD); + // make sure we have a struct with no fields (unit struct) + if let ty::Adt(def, ..) = cx.typeck_results().expr_ty(expr).kind(); + if def.is_struct() && def.is_payloadfree() + && !def.non_enum_variant().is_field_list_non_exhaustive() + && !is_from_proc_macro(cx, expr); + then { + span_lint_and_sugg( + cx, + DEFAULT_CONSTRUCTED_UNIT_STRUCT, + qpath.last_segment_span(), + "Use of `default` to create a unit struct.", + "remove this call to `default`", + String::new(), + Applicability::MachineApplicable, + ) + } + ); + } +} diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 48dbecc9f6a..9af0b17e27b 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -94,6 +94,7 @@ mod crate_in_macro_def; mod create_dir; mod dbg_macro; mod default; +mod default_constructed_unit_struct; mod default_instead_of_iter_empty; mod default_numeric_fallback; mod default_union_representation; @@ -970,6 +971,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: store.register_late_pass(|_| Box::new(manual_slice_size_calculation::ManualSliceSizeCalculation)); store.register_early_pass(|| Box::new(suspicious_doc_comments::SuspiciousDocComments)); store.register_late_pass(|_| Box::new(items_after_test_module::ItemsAfterTestModule)); + store.register_late_pass(|_| Box::new(default_constructed_unit_struct::DefaultConstructedUnitStruct)); // add lints here, do not remove this comment, it's used in `new_lint` } diff --git a/tests/ui/default_constructed_unit_struct.rs b/tests/ui/default_constructed_unit_struct.rs new file mode 100644 index 00000000000..b64da9b863a --- /dev/null +++ b/tests/ui/default_constructed_unit_struct.rs @@ -0,0 +1,72 @@ +#![allow(unused)] +#![warn(clippy::default_constructed_unit_struct)] +use std::marker::PhantomData; + +#[derive(Default)] +struct UnitStruct; + +#[derive(Default)] +struct TupleStruct(usize); + +// no lint for derived impl +#[derive(Default)] +struct NormalStruct { + inner: PhantomData, +} + +struct NonDefaultStruct; + +impl NonDefaultStruct { + fn default() -> Self { + Self + } +} + +#[derive(Default)] +enum SomeEnum { + #[default] + Unit, + Tuple(UnitStruct), + Struct { + inner: usize, + }, +} + +impl NormalStruct { + fn new() -> Self { + // should lint + Self { + inner: PhantomData::default(), + } + } +} + +#[derive(Default)] +struct GenericStruct { + t: T, +} + +impl GenericStruct { + fn new() -> Self { + // should not lint + Self { t: T::default() } + } +} + +#[derive(Default)] +#[non_exhaustive] +struct NonExhaustiveStruct; + +fn main() { + // should lint + let _ = PhantomData::::default(); + let _: PhantomData = PhantomData::default(); + let _ = UnitStruct::default(); + + // should not lint + let _ = TupleStruct::default(); + let _ = NormalStruct::default(); + let _ = NonExhaustiveStruct::default(); + let _ = SomeEnum::default(); + let _ = NonDefaultStruct::default(); +} diff --git a/tests/ui/default_constructed_unit_struct.stderr b/tests/ui/default_constructed_unit_struct.stderr new file mode 100644 index 00000000000..13439414f4a --- /dev/null +++ b/tests/ui/default_constructed_unit_struct.stderr @@ -0,0 +1,28 @@ +error: Use of `default` to create a unit struct. + --> $DIR/default_constructed_unit_struct.rs:39:33 + | +LL | inner: PhantomData::default(), + | ^^^^^^^ help: remove this call to `default` + | + = note: `-D clippy::default-constructed-unit-struct` implied by `-D warnings` + +error: Use of `default` to create a unit struct. + --> $DIR/default_constructed_unit_struct.rs:62:35 + | +LL | let _ = PhantomData::::default(); + | ^^^^^^^ help: remove this call to `default` + +error: Use of `default` to create a unit struct. + --> $DIR/default_constructed_unit_struct.rs:63:44 + | +LL | let _: PhantomData = PhantomData::default(); + | ^^^^^^^ help: remove this call to `default` + +error: Use of `default` to create a unit struct. + --> $DIR/default_constructed_unit_struct.rs:64:25 + | +LL | let _ = UnitStruct::default(); + | ^^^^^^^ help: remove this call to `default` + +error: aborting due to 4 previous errors +