use rustc::hir::def_id::DefId; use rustc::hir; use rustc::lint::*; use rustc::ty::{self, Ty}; use syntax::codemap::Span; use crate::utils::paths; use crate::utils::{get_trait_def_id, implements_trait, in_external_macro, return_ty, same_tys, span_lint_and_then}; use crate::utils::sugg::DiagnosticBuilderExt; /// **What it does:** Checks for types with a `fn new() -> Self` method and no /// implementation of /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html). /// /// **Why is this bad?** The user might expect to be able to use /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the /// type can be constructed without arguments. /// /// **Known problems:** Hopefully none. /// /// **Example:** /// /// ```rust,ignore /// struct Foo(Bar); /// /// impl Foo { /// fn new() -> Self { /// Foo(Bar::new()) /// } /// } /// ``` /// /// Instead, use: /// /// ```rust /// struct Foo(Bar); /// /// impl Default for Foo { /// fn default() -> Self { /// Foo(Bar::new()) /// } /// } /// ``` /// /// You can also have `new()` call `Default::default()`. declare_clippy_lint! { pub NEW_WITHOUT_DEFAULT, style, "`fn new() -> Self` method without `Default` implementation" } /// **What it does:** Checks for types with a `fn new() -> Self` method /// and no implementation of /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html), /// where the `Default` can be derived by `#[derive(Default)]`. /// /// **Why is this bad?** The user might expect to be able to use /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the /// type can be constructed without arguments. /// /// **Known problems:** Hopefully none. /// /// **Example:** /// /// ```rust,ignore /// struct Foo; /// /// impl Foo { /// fn new() -> Self { /// Foo /// } /// } /// ``` /// /// Just prepend `#[derive(Default)]` before the `struct` definition. declare_clippy_lint! { pub NEW_WITHOUT_DEFAULT_DERIVE, style, "`fn new() -> Self` without `#[derive]`able `Default` implementation" } #[derive(Copy, Clone)] pub struct NewWithoutDefault; impl LintPass for NewWithoutDefault { fn get_lints(&self) -> LintArray { lint_array!(NEW_WITHOUT_DEFAULT, NEW_WITHOUT_DEFAULT_DERIVE) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault { fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) { if let hir::ItemImpl(_, _, _, _, None, _, ref items) = item.node { for assoc_item in items { if let hir::AssociatedItemKind::Method { has_self: false } = assoc_item.kind { let impl_item = cx.tcx.hir.impl_item(assoc_item.id); if in_external_macro(cx, impl_item.span) { return; } if let hir::ImplItemKind::Method(ref sig, _) = impl_item.node { let name = impl_item.name; let id = impl_item.id; if sig.constness == hir::Constness::Const { // can't be implemented by default return; } if impl_item.generics.params.iter().any(|gen| gen.is_type_param()) { // when the result of `new()` depends on a type parameter we should not require // an // impl of `Default` return; } if sig.decl.inputs.is_empty() && name == "new" && cx.access_levels.is_reachable(id) { let self_ty = cx.tcx .type_of(cx.tcx.hir.local_def_id(cx.tcx.hir.get_parent(id))); if_chain! { if same_tys(cx, self_ty, return_ty(cx, id)); if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT); if !implements_trait(cx, self_ty, default_trait_id, &[]); then { if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) { span_lint_and_then( cx, NEW_WITHOUT_DEFAULT_DERIVE, impl_item.span, &format!("you should consider deriving a `Default` implementation for `{}`", self_ty), |db| { db.suggest_item_with_attr(cx, sp, "try this", "#[derive(Default)]"); }); } else { span_lint_and_then( cx, NEW_WITHOUT_DEFAULT, impl_item.span, &format!("you should consider adding a `Default` implementation for `{}`", self_ty), |db| { db.suggest_prepend_item( cx, item.span, "try this", &create_new_without_default_suggest_msg(self_ty), ); }, ); } } } } } } } } } } fn create_new_without_default_suggest_msg(ty: Ty) -> String { #[cfg_attr(rustfmt, rustfmt_skip)] format!( "impl Default for {} {{ fn default() -> Self {{ Self::new() }} }}", ty) } fn can_derive_default<'t, 'c>(ty: Ty<'t>, cx: &LateContext<'c, 't>, default_trait_id: DefId) -> Option { match ty.sty { ty::TyAdt(adt_def, substs) if adt_def.is_struct() => { for field in adt_def.all_fields() { let f_ty = field.ty(cx.tcx, substs); if !implements_trait(cx, f_ty, default_trait_id, &[]) { return None; } } Some(cx.tcx.def_span(adt_def.did)) }, _ => None, } }