231 lines
9.5 KiB
Rust
231 lines
9.5 KiB
Rust
use crate::utils::paths;
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use crate::utils::sugg::DiagnosticBuilderExt;
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use crate::utils::{get_trait_def_id, implements_trait, return_ty, same_tys, span_lint_hir_and_then};
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use if_chain::if_chain;
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use rustc::hir;
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use rustc::hir::def_id::DefId;
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use rustc::hir::HirIdSet;
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use rustc::impl_lint_pass;
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use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
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use rustc::ty::{self, Ty};
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use rustc_errors::Applicability;
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use rustc_session::declare_tool_lint;
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use rustc_span::source_map::Span;
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declare_clippy_lint! {
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/// **What it does:** Checks for types with a `fn new() -> Self` method and no
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/// implementation of
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/// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html).
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///
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/// It detects both the case when a manual
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/// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html)
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/// implementation is required and also when it can be created with
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/// `#[derive(Default)]`
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///
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/// **Why is this bad?** The user might expect to be able to use
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/// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the
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/// type can be constructed without arguments.
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///
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/// **Known problems:** Hopefully none.
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///
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/// **Example:**
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///
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/// ```ignore
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/// struct Foo(Bar);
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///
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/// impl Foo {
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/// fn new() -> Self {
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/// Foo(Bar::new())
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/// }
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/// }
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/// ```
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///
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/// Instead, use:
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///
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/// ```ignore
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/// struct Foo(Bar);
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///
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/// impl Default for Foo {
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/// fn default() -> Self {
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/// Foo(Bar::new())
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/// }
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/// }
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/// ```
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///
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/// Or, if
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/// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html)
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/// can be derived by `#[derive(Default)]`:
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///
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/// ```rust
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/// struct Foo;
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///
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/// impl Foo {
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/// fn new() -> Self {
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/// Foo
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/// }
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/// }
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/// ```
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///
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/// Instead, use:
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///
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/// ```rust
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/// #[derive(Default)]
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/// struct Foo;
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///
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/// impl Foo {
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/// fn new() -> Self {
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/// Foo
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/// }
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/// }
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/// ```
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///
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/// You can also have `new()` call `Default::default()`.
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pub NEW_WITHOUT_DEFAULT,
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style,
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"`fn new() -> Self` method without `Default` implementation"
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}
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#[derive(Clone, Default)]
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pub struct NewWithoutDefault {
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impling_types: Option<HirIdSet>,
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}
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impl_lint_pass!(NewWithoutDefault => [NEW_WITHOUT_DEFAULT]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item<'_>) {
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if let hir::ItemKind::Impl(_, _, _, _, None, _, items) = item.kind {
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for assoc_item in items {
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if let hir::AssocItemKind::Method { has_self: false } = assoc_item.kind {
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let impl_item = cx.tcx.hir().impl_item(assoc_item.id);
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if in_external_macro(cx.sess(), impl_item.span) {
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return;
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}
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if let hir::ImplItemKind::Method(ref sig, _) = impl_item.kind {
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let name = impl_item.ident.name;
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let id = impl_item.hir_id;
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if sig.header.constness == hir::Constness::Const {
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// can't be implemented by default
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return;
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}
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if sig.header.unsafety == hir::Unsafety::Unsafe {
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// can't be implemented for unsafe new
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return;
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}
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if impl_item.generics.params.iter().any(|gen| match gen.kind {
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hir::GenericParamKind::Type { .. } => true,
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_ => false,
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}) {
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// when the result of `new()` depends on a type parameter we should not require
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// an
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// impl of `Default`
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return;
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}
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if sig.decl.inputs.is_empty() && name == sym!(new) && cx.access_levels.is_reachable(id) {
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let self_did = cx.tcx.hir().local_def_id(cx.tcx.hir().get_parent_item(id));
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let self_ty = cx.tcx.type_of(self_did);
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if_chain! {
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if same_tys(cx, self_ty, return_ty(cx, id));
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if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
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then {
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if self.impling_types.is_none() {
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let mut impls = HirIdSet::default();
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cx.tcx.for_each_impl(default_trait_id, |d| {
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if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
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if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(ty_def.did) {
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impls.insert(hir_id);
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}
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}
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});
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self.impling_types = Some(impls);
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}
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// Check if a Default implementation exists for the Self type, regardless of
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// generics
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if_chain! {
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if let Some(ref impling_types) = self.impling_types;
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if let Some(self_def) = cx.tcx.type_of(self_did).ty_adt_def();
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if self_def.did.is_local();
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then {
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let self_id = cx.tcx.hir().local_def_id_to_hir_id(self_def.did.to_local());
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if impling_types.contains(&self_id) {
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return;
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}
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}
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}
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if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) {
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span_lint_hir_and_then(
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cx,
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NEW_WITHOUT_DEFAULT,
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id,
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impl_item.span,
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&format!(
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"you should consider deriving a `Default` implementation for `{}`",
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self_ty
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),
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|db| {
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db.suggest_item_with_attr(
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cx,
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sp,
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"try this",
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"#[derive(Default)]",
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Applicability::MaybeIncorrect,
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);
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});
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} else {
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span_lint_hir_and_then(
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cx,
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NEW_WITHOUT_DEFAULT,
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id,
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impl_item.span,
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&format!(
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"you should consider adding a `Default` implementation for `{}`",
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self_ty
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),
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|db| {
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db.suggest_prepend_item(
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cx,
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item.span,
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"try this",
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&create_new_without_default_suggest_msg(self_ty),
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Applicability::MaybeIncorrect,
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);
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},
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);
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}
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}
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}
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}
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}
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}
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}
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}
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}
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}
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fn create_new_without_default_suggest_msg(ty: Ty<'_>) -> String {
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#[rustfmt::skip]
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format!(
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"impl Default for {} {{
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fn default() -> Self {{
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Self::new()
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}}
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}}", ty)
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}
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fn can_derive_default<'t, 'c>(ty: Ty<'t>, cx: &LateContext<'c, 't>, default_trait_id: DefId) -> Option<Span> {
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match ty.kind {
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ty::Adt(adt_def, substs) if adt_def.is_struct() => {
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for field in adt_def.all_fields() {
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let f_ty = field.ty(cx.tcx, substs);
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if !implements_trait(cx, f_ty, default_trait_id, &[]) {
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return None;
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}
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}
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Some(cx.tcx.def_span(adt_def.did))
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},
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_ => None,
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}
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}
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