// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use crate::utils::paths; use crate::utils::sugg::DiagnosticBuilderExt; use crate::utils::{get_trait_def_id, implements_trait, return_ty, same_tys, span_lint_node_and_then}; use if_chain::if_chain; use rustc::hir; use rustc::hir::def_id::DefId; use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass}; use rustc::ty::{self, Ty}; use rustc::util::nodemap::NodeSet; use rustc::{declare_tool_lint, lint_array}; use rustc_errors::Applicability; use syntax::source_map::Span; /// **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). /// /// It detects both the case when a manual /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) /// implementation is required and also when it can be created with /// `#[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 /// 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()) /// } /// } /// ``` /// /// Or, if /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) /// can be derived by `#[derive(Default)]`: /// /// ```rust /// struct Foo; /// /// impl Foo { /// fn new() -> Self { /// Foo /// } /// } /// ``` /// /// Instead, use: /// /// ```rust /// #[derive(Default)] /// struct Foo; /// /// impl Foo { /// fn new() -> Self { /// Foo /// } /// } /// ``` /// /// You can also have `new()` call `Default::default()`. declare_clippy_lint! { pub NEW_WITHOUT_DEFAULT, style, "`fn new() -> Self` method without `Default` implementation" } #[derive(Clone, Default)] pub struct NewWithoutDefault { impling_types: Option, } impl LintPass for NewWithoutDefault { fn get_lints(&self) -> LintArray { lint_array!(NEW_WITHOUT_DEFAULT) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault { fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) { if let hir::ItemKind::Impl(_, _, _, _, 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.sess(), impl_item.span) { return; } if let hir::ImplItemKind::Method(ref sig, _) = impl_item.node { let name = impl_item.ident.name; let id = impl_item.id; if sig.header.constness == hir::Constness::Const { // can't be implemented by default return; } if sig.header.unsafety == hir::Unsafety::Unsafe { // can't be implemented for unsafe new return; } if impl_item.generics.params.iter().any(|gen| match gen.kind { hir::GenericParamKind::Type { .. } => true, _ => false, }) { // 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_did = cx.tcx.hir().local_def_id(cx.tcx.hir().get_parent(id)); let self_ty = cx.tcx.type_of(self_did); 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); then { if self.impling_types.is_none() { let mut impls = NodeSet::default(); cx.tcx.for_each_impl(default_trait_id, |d| { if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() { if let Some(node_id) = cx.tcx.hir().as_local_node_id(ty_def.did) { impls.insert(node_id); } } }); self.impling_types = Some(impls); } // Check if a Default implementation exists for the Self type, regardless of // generics if_chain! { if let Some(ref impling_types) = self.impling_types; if let Some(self_def) = cx.tcx.type_of(self_did).ty_adt_def(); if self_def.did.is_local(); then { let self_id = cx.tcx.hir().local_def_id_to_node_id(self_def.did.to_local()); if impling_types.contains(&self_id) { return; } } } if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) { span_lint_node_and_then( cx, NEW_WITHOUT_DEFAULT, id, 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)]", Applicability::MaybeIncorrect, ); }); } else { span_lint_node_and_then( cx, NEW_WITHOUT_DEFAULT, id, 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), Applicability::MaybeIncorrect, ); }, ); } } } } } } } } } } fn create_new_without_default_suggest_msg(ty: Ty<'_>) -> String { #[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::Adt(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, } }