rust-clippy/clippy_lints/src/new_without_default.rs

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use rustc::hir::intravisit::FnKind;
use rustc::hir::def_id::DefId;
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use rustc::hir;
use rustc::lint::*;
use rustc::ty::{self, Ty};
use syntax::ast;
use syntax::codemap::Span;
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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())
/// }
/// }
/// ```
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///
/// Instead, use:
///
/// ```rust
/// struct Foo(Bar);
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///
/// impl Default for Foo {
/// fn default() -> Self {
/// Foo(Bar::new())
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/// }
/// }
/// ```
///
/// 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"
}
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#[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,
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id: ast::NodeId,
) {
if in_external_macro(cx, span) {
return;
}
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if let FnKind::Method(name, sig, _, _) = kind {
if sig.constness == hir::Constness::Const {
// can't be implemented by default
return;
}
if !cx.generics.expect("method must have generics").ty_params.is_empty() {
// when the result of `new()` depends on a type parameter we should not require
// an
// impl of `Default`
return;
}
if decl.inputs.is_empty() && name == "new" && cx.access_levels.is_reachable(id) {
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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, 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!(
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"impl Default for {} {{
fn default() -> Self {{
Self::new()
}}
}}",
self_ty));
});
}
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}
}
}
}
}
}
fn can_derive_default<'t, 'c>(ty: Ty<'t>, cx: &LateContext<'c, 't>, default_trait_id: DefId) -> Option<Span> {
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;
}
}
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Some(cx.tcx.def_span(adt_def.did))
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},
_ => None,
}
}