rust-clippy/clippy_lints/src/new_without_default.rs

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use crate::utils::paths;
use crate::utils::sugg::DiagnosticBuilderExt;
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;
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;
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declare_clippy_lint! {
/// **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:**
///
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/// ```ignore
/// struct Foo(Bar);
///
/// impl Foo {
/// fn new() -> Self {
/// Foo(Bar::new())
/// }
/// }
/// ```
///
/// Instead, use:
///
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/// ```ignore
/// 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()`.
pub NEW_WITHOUT_DEFAULT,
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style,
"`fn new() -> Self` method without `Default` implementation"
}
#[derive(Clone, Default)]
pub struct NewWithoutDefault {
impling_types: Option<NodeSet>,
}
impl LintPass for NewWithoutDefault {
fn get_lints(&self) -> LintArray {
lint_array!(NEW_WITHOUT_DEFAULT)
}
fn name(&self) -> &'static str {
"NewWithoutDefault"
}
}
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, _, ref items) = item.node {
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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);
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if in_external_macro(cx.sess(), impl_item.span) {
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return;
}
if let hir::ImplItemKind::Method(ref sig, _) = impl_item.node {
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let name = impl_item.ident.name;
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let id = impl_item.hir_id;
if sig.header.constness == hir::Constness::Const {
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// can't be implemented by default
return;
}
if sig.header.unsafety == hir::Unsafety::Unsafe {
// can't be implemented for unsafe new
return;
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}
if impl_item.generics.params.iter().any(|gen| match gen.kind {
hir::GenericParamKind::Type { .. } => true,
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_ => false,
}) {
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// 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) {
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let self_did = cx.tcx.hir().local_def_id_from_hir_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);
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;
}
}
}
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if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) {
span_lint_hir_and_then(
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cx,
NEW_WITHOUT_DEFAULT,
id,
impl_item.span,
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&format!(
"you should consider deriving a `Default` implementation for `{}`",
self_ty
),
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|db| {
db.suggest_item_with_attr(
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cx,
sp,
"try this",
"#[derive(Default)]",
Applicability::MaybeIncorrect,
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);
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});
} else {
span_lint_hir_and_then(
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cx,
NEW_WITHOUT_DEFAULT,
id,
impl_item.span,
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&format!(
"you should consider adding a `Default` implementation for `{}`",
self_ty
),
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|db| {
db.suggest_prepend_item(
cx,
item.span,
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"try this",
&create_new_without_default_suggest_msg(self_ty),
Applicability::MaybeIncorrect,
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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!(
"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<Span> {
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;
}
}
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Some(cx.tcx.def_span(adt_def.did))
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},
_ => None,
}
}