1 use rustc::hir::intravisit::FnKind;
2 use rustc::hir::def_id::DefId;
5 use rustc::ty::{self, Ty};
7 use syntax::codemap::Span;
9 use utils::{get_trait_def_id, implements_trait, in_external_macro, return_ty, same_tys, span_lint_and_then};
10 use utils::sugg::DiagnosticBuilderExt;
12 /// **What it does:** Checks for types with a `fn new() -> Self` method and no
14 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html).
16 /// **Why is this bad?** The user might expect to be able to use
17 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the
18 /// type can be constructed without arguments.
20 /// **Known problems:** Hopefully none.
28 /// fn new() -> Self {
39 /// impl Default for Foo {
40 /// fn default() -> Self {
46 /// You can also have `new()` call `Default::default()`.
48 pub NEW_WITHOUT_DEFAULT,
50 "`fn new() -> Self` method without `Default` implementation"
53 /// **What it does:** Checks for types with a `fn new() -> Self` method
54 /// and no implementation of
55 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html),
56 /// where the `Default` can be derived by `#[derive(Default)]`.
58 /// **Why is this bad?** The user might expect to be able to use
59 /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the
60 /// type can be constructed without arguments.
62 /// **Known problems:** Hopefully none.
70 /// fn new() -> Self {
76 /// Just prepend `#[derive(Default)]` before the `struct` definition.
78 pub NEW_WITHOUT_DEFAULT_DERIVE,
80 "`fn new() -> Self` without `#[derive]`able `Default` implementation"
83 #[derive(Copy, Clone)]
84 pub struct NewWithoutDefault;
86 impl LintPass for NewWithoutDefault {
87 fn get_lints(&self) -> LintArray {
88 lint_array!(NEW_WITHOUT_DEFAULT, NEW_WITHOUT_DEFAULT_DERIVE)
92 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault {
95 cx: &LateContext<'a, 'tcx>,
97 decl: &'tcx hir::FnDecl,
102 if in_external_macro(cx, span) {
106 if let FnKind::Method(name, sig, _, _) = kind {
107 if sig.constness == hir::Constness::Const {
108 // can't be implemented by default
111 if !sig.generics.ty_params.is_empty() {
112 // when the result of `new()` depends on a type parameter we should not require
117 if decl.inputs.is_empty() && name == "new" && cx.access_levels.is_reachable(id) {
119 .type_of(cx.tcx.hir.local_def_id(cx.tcx.hir.get_parent(id)));
121 if same_tys(cx, self_ty, return_ty(cx, id));
122 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
123 if !implements_trait(cx, self_ty, default_trait_id, &[]);
125 if let Some(sp) = can_derive_default(self_ty, cx, default_trait_id) {
126 span_lint_and_then(cx,
127 NEW_WITHOUT_DEFAULT_DERIVE, span,
128 &format!("you should consider deriving a \
129 `Default` implementation for `{}`",
132 db.suggest_item_with_attr(cx, sp, "try this", "#[derive(Default)]");
135 span_lint_and_then(cx,
136 NEW_WITHOUT_DEFAULT, span,
137 &format!("you should consider adding a \
138 `Default` implementation for `{}`",
141 db.suggest_prepend_item(cx,
145 "impl Default for {} {{
146 fn default() -> Self {{
160 fn can_derive_default<'t, 'c>(ty: Ty<'t>, cx: &LateContext<'c, 't>, default_trait_id: DefId) -> Option<Span> {
162 ty::TyAdt(adt_def, substs) if adt_def.is_struct() => {
163 for field in adt_def.all_fields() {
164 let f_ty = field.ty(cx.tcx, substs);
165 if !implements_trait(cx, f_ty, default_trait_id, &[]) {
169 Some(cx.tcx.def_span(adt_def.did))