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https://github.com/rust-lang/rust-clippy
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Auto merge of #5616 - euclio:no-derive-suggestion, r=phansch,flip1995
new_without_default: do not suggest deriving --- changelog: do not suggest deriving `Default` in `new_without_default` This commit changes the behavior of the `new_without_default` lint to not suggest deriving `Default`. This suggestion is misleading if the `new` implementation does something different than what a derived `Default` implementation would do, because then the two methods would not be equivalent. Instead, the `can_derive_default` check is removed, and we always suggest implementing `Default` in terms of `new()`.
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commit
c41916d9bd
3 changed files with 64 additions and 100 deletions
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@ -1,27 +1,20 @@
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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 crate::utils::{get_trait_def_id, return_ty, same_tys, span_lint_hir_and_then};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir as 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_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty::{self, Ty};
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use rustc_middle::ty::Ty;
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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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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@ -40,46 +33,17 @@ declare_clippy_lint! {
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/// }
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/// ```
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///
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/// Instead, use:
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/// To fix the lint, and a `Default` implementation that delegates to `new`:
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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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/// Foo::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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@ -158,46 +122,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault {
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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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|diag| {
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diag.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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|diag| {
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diag.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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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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|diag| {
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diag.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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@ -217,18 +160,3 @@ fn create_new_without_default_suggest_msg(ty: Ty<'_>) -> String {
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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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@ -148,4 +148,15 @@ impl AllowDerive {
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}
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}
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pub struct NewNotEqualToDerive {
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foo: i32,
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}
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impl NewNotEqualToDerive {
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// This `new` implementation is not equal to a derived `Default`, so do not suggest deriving.
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pub fn new() -> Self {
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NewNotEqualToDerive { foo: 1 }
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}
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}
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fn main() {}
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@ -1,4 +1,4 @@
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error: you should consider deriving a `Default` implementation for `Foo`
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error: you should consider adding a `Default` implementation for `Foo`
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--> $DIR/new_without_default.rs:8:5
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LL | / pub fn new() -> Foo {
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@ -9,10 +9,14 @@ LL | | }
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= note: `-D clippy::new-without-default` implied by `-D warnings`
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help: try this
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LL | #[derive(Default)]
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LL | impl Default for Foo {
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LL | fn default() -> Self {
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LL | Self::new()
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LL | }
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LL | }
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error: you should consider deriving a `Default` implementation for `Bar`
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error: you should consider adding a `Default` implementation for `Bar`
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--> $DIR/new_without_default.rs:16:5
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LL | / pub fn new() -> Self {
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@ -22,7 +26,11 @@ LL | | }
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help: try this
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LL | #[derive(Default)]
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LL | impl Default for Bar {
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LL | fn default() -> Self {
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LL | Self::new()
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LL | }
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LL | }
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error: you should consider adding a `Default` implementation for `LtKo<'c>`
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@ -42,5 +50,22 @@ LL | }
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LL | }
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error: aborting due to 3 previous errors
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error: you should consider adding a `Default` implementation for `NewNotEqualToDerive`
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--> $DIR/new_without_default.rs:157:5
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LL | / pub fn new() -> Self {
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LL | | NewNotEqualToDerive { foo: 1 }
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LL | | }
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| |_____^
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help: try this
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LL | impl Default for NewNotEqualToDerive {
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LL | fn default() -> Self {
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LL | Self::new()
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LL | }
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LL | }
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error: aborting due to 4 previous errors
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