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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::is_must_use_ty;
use clippy_utils::{nth_arg, return_ty};
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{Body, FnDecl, OwnerId, TraitItem, TraitItemKind};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{sym, Span};
declare_clippy_lint! {
/// ### What it does
/// This lint warns when a method returning `Self` doesn't have the `#[must_use]` attribute.
///
/// ### Why is this bad?
/// Methods returning `Self` often create new values, having the `#[must_use]` attribute
/// prevents users from "forgetting" to use the newly created value.
///
/// The `#[must_use]` attribute can be added to the type itself to ensure that instances
/// are never forgotten. Functions returning a type marked with `#[must_use]` will not be
/// linted, as the usage is already enforced by the type attribute.
///
/// ### Limitations
/// This lint is only applied on methods taking a `self` argument. It would be mostly noise
/// if it was added on constructors for example.
///
/// ### Example
/// ```rust
/// pub struct Bar;
/// impl Bar {
/// // Missing attribute
/// pub fn bar(&self) -> Self {
/// Self
/// }
/// }
/// ```
///
/// Use instead:
/// ```rust
/// # {
/// // It's better to have the `#[must_use]` attribute on the method like this:
/// pub struct Bar;
/// impl Bar {
/// #[must_use]
/// pub fn bar(&self) -> Self {
/// Self
/// }
/// }
/// # }
///
/// # {
/// // Or on the type definition like this:
/// #[must_use]
/// pub struct Bar;
/// impl Bar {
/// pub fn bar(&self) -> Self {
/// Self
/// }
/// }
/// # }
/// ```
#[clippy::version = "1.59.0"]
pub RETURN_SELF_NOT_MUST_USE,
pedantic,
"missing `#[must_use]` annotation on a method returning `Self`"
}
declare_lint_pass!(ReturnSelfNotMustUse => [RETURN_SELF_NOT_MUST_USE]);
fn check_method(cx: &LateContext<'_>, decl: &FnDecl<'_>, fn_def: LocalDefId, span: Span, owner_id: OwnerId) {
if_chain! {
// If it comes from an external macro, better ignore it.
if !in_external_macro(cx.sess(), span);
if decl.implicit_self.has_implicit_self();
// We only show this warning for public exported methods.
if cx.effective_visibilities.is_exported(fn_def);
// We don't want to emit this lint if the `#[must_use]` attribute is already there.
if !cx.tcx.hir().attrs(owner_id.into()).iter().any(|attr| attr.has_name(sym::must_use));
if cx.tcx.visibility(fn_def.to_def_id()).is_public();
let ret_ty = return_ty(cx, owner_id);
let self_arg = nth_arg(cx, owner_id, 0);
// If `Self` has the same type as the returned type, then we want to warn.
//
// For this check, we don't want to remove the reference on the returned type because if
// there is one, we shouldn't emit a warning!
if self_arg.peel_refs() == ret_ty;
// If `Self` is already marked as `#[must_use]`, no need for the attribute here.
if !is_must_use_ty(cx, ret_ty);
then {
span_lint_and_help(
cx,
RETURN_SELF_NOT_MUST_USE,
span,
"missing `#[must_use]` attribute on a method returning `Self`",
None,
"consider adding the `#[must_use]` attribute to the method or directly to the `Self` type"
);
}
}
}
impl<'tcx> LateLintPass<'tcx> for ReturnSelfNotMustUse {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'tcx>,
_: &'tcx Body<'tcx>,
span: Span,
fn_def: LocalDefId,
) {
if_chain! {
// We are only interested in methods, not in functions or associated functions.
if matches!(kind, FnKind::Method(_, _));
if let Some(impl_def) = cx.tcx.impl_of_method(fn_def.to_def_id());
// We don't want this method to be te implementation of a trait because the
// `#[must_use]` should be put on the trait definition directly.
if cx.tcx.trait_id_of_impl(impl_def).is_none();
then {
let hir_id = cx.tcx.hir().local_def_id_to_hir_id(fn_def);
check_method(cx, decl, fn_def, span, hir_id.expect_owner());
}
}
}
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'tcx>) {
if let TraitItemKind::Fn(ref sig, _) = item.kind {
check_method(cx, sig.decl, item.owner_id.def_id, item.span, item.owner_id);
}
}
}
|
