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Fix let_underscore_drop implements Drop logic

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This fixes false positives and false negatives.
This commit is contained in:
Cameron Steffen 2021-02-05 14:45:24 -06:00
parent 357c6a7e27
commit ac5e9c8d26
2 changed files with 10 additions and 11 deletions
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13
clippy_lints/src/let_underscore.rs
View file

@ -5,7 +5,7 @@ use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::{implements_trait, is_must_use_func_call, is_must_use_ty, match_type, paths, span_lint_and_help};
use crate::utils::{is_must_use_func_call, is_must_use_ty, match_type, paths, span_lint_and_help};
declare_clippy_lint! {
/// **What it does:** Checks for `let _ = <expr>`
@ -125,15 +125,6 @@ impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
});
let implements_drop = cx.tcx.lang_items().drop_trait().map_or(false, |drop_trait|
init_ty.walk().any(|inner| match inner.unpack() {
GenericArgKind::Type(inner_ty) => {
implements_trait(cx, inner_ty, drop_trait, &[])
},
GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
})
);
if contains_sync_guard {
span_lint_and_help(
cx,
@ -144,7 +135,7 @@ impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
"consider using an underscore-prefixed named \
binding or dropping explicitly with `std::mem::drop`"
)
} else if implements_drop {
} else if init_ty.needs_drop(cx.tcx, cx.param_env) {
span_lint_and_help(
cx,
LET_UNDERSCORE_DROP,

8
tests/ui/let_underscore_drop.rs
View file

@ -16,4 +16,12 @@ fn main() {
let _ = Box::new(());
let _ = Droppable;
let _ = Some(Droppable);
// no lint for reference
let _ = droppable_ref();
}
#[must_use]
fn droppable_ref() -> &'static mut Droppable {
unimplemented!()
}