use rustc::hir::intravisit::FnKind; use rustc::hir::def_id::DefId; use rustc::hir; use rustc::lint::*; use rustc::ty; use syntax::ast; use syntax::codemap::Span; use utils::paths; use utils::{get_trait_def_id, implements_trait, in_external_macro, return_ty, same_tys, span_lint_and_then}; use 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_lint! { pub NEW_WITHOUT_DEFAULT, Warn, "`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_lint! { pub NEW_WITHOUT_DEFAULT_DERIVE, Warn, "`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_fn( &mut self, cx: &LateContext<'a, 'tcx>, kind: FnKind<'tcx>, decl: &'tcx hir::FnDecl, _: &'tcx hir::Body, span: Span, id: ast::NodeId ) { if in_external_macro(cx, span) { return; } if let FnKind::Method(name, sig, _, _) = kind { if sig.constness == hir::Constness::Const { // can't be implemented by default return; } if decl.inputs.is_empty() && name.as_str() == "new" && cx.access_levels.is_reachable(id) { let self_ty = cx.tcx .item_type(cx.tcx.hir.local_def_id(cx.tcx.hir.get_parent(id))); if_let_chain!{[ self_ty.walk_shallow().next().is_none(), // implements_trait does not work with generics same_tys(cx, self_ty, return_ty(cx, id), id), let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT), !implements_trait(cx, self_ty, default_trait_id, &[], None) ], { if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) { span_lint_and_then(cx, NEW_WITHOUT_DEFAULT_DERIVE, 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, span, &format!("you should consider adding a \ `Default` implementation for `{}`", self_ty), |db| { db.suggest_prepend_item(cx, span, "try this", &format!( "impl Default for {} {{ fn default() -> Self {{ Self::new() }} }}", self_ty)); }); } }} } } } } fn can_derive_default<'t, 'c>(ty: 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, &[], None) { return None; } } cx.tcx.hir.span_if_local(adt_def.did) }, _ => None, } }