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// `#![no_std]`: these arrive with the standard prelude and name no path, so a `std::`
// search cannot see them - and a `#[derive]` can use them without the name appearing
// in this file at all, which is why they are not trimmed by inspection.
use alloc::borrow::ToOwned;
use alloc::boxed::Box;
use alloc::format;
use alloc::string::{String, ToString};
use alloc::vec;
use alloc::vec::Vec;
use crate::rustc_hir::{Arm, Expr, ExprKind, Node, StmtKind};
use crate::rustc_lint_defs::{declare_lint, declare_lint_pass};
use crate::rustc_middle::ty;
use crate::rustc_span::sym;
use crate::rustc_lint::diagnostics::{
DropCopyDiag, DropInPlaceCopyDiag, DropInPlaceRefDiag, DropRefDiag, ForgetCopyDiag,
ForgetRefDiag, UndroppedManuallyDropsDiag, UndroppedManuallyDropsInPlaceDiag,
UndroppedManuallyDropsInPlaceSuggestion, UndroppedManuallyDropsSuggestion,
UseLetUnderscoreIgnoreSuggestion,
};
use crate::rustc_lint::{LateContext, LateLintPass, LintContext};
declare_lint! {
/// The `dropping_references` lint checks for calls to `core::mem::drop`
/// and `core::ptr::drop_in_place` where the dropped type is a reference instead of
/// an owned value.
///
/// ### Explanation
///
/// Calling `drop` on a reference will only drop the
/// reference itself, which is a no-op. It will not call the `drop` method (from
/// the `Drop` trait implementation) on the underlying referenced value, which
/// is likely what was intended.
pub DROPPING_REFERENCES,
Warn,
"calls to `drop` and `drop_in_place` where the dropped type is a reference instead of an owned value"
}
declare_lint! {
/// The `forgetting_references` lint checks for calls to `core::mem::forget` with a reference
/// instead of an owned value.
///
/// ### Example
///
/// ```rust
/// let x = Box::new(1);
/// core::mem::forget(&x); // Should have been forget(x), x will still be dropped
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Calling `forget` on a reference will only forget the
/// reference itself, which is a no-op. It will not forget the underlying
/// referenced value, which is likely what was intended.
pub FORGETTING_REFERENCES,
Warn,
"calls to `core::mem::forget` with a reference instead of an owned value"
}
declare_lint! {
/// The `dropping_copy_types` lint checks for calls to `core::mem::drop`
/// and `core::ptr::drop_in_place` where the dropped value implements the `Copy` trait.
///
/// ### Example
///
/// ```rust
/// let x: i32 = 42; // i32 implements Copy
/// core::mem::drop(x); // A copy of x is passed to the function, leaving the
/// // original unaffected
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Calling `core::mem::drop` [does nothing for types that
/// implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html), since the
/// value will be copied and moved into the function on invocation.
pub DROPPING_COPY_TYPES,
Warn,
"calls to `drop` and `drop_in_place` where the dropped value implements Copy"
}
declare_lint! {
/// The `forgetting_copy_types` lint checks for calls to `core::mem::forget` with a value
/// that derives the Copy trait.
///
/// ### Example
///
/// ```rust
/// let x: i32 = 42; // i32 implements Copy
/// core::mem::forget(x); // A copy of x is passed to the function, leaving the
/// // original unaffected
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Calling `core::mem::forget` [does nothing for types that
/// implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html) since the
/// value will be copied and moved into the function on invocation.
///
/// An alternative, but also valid, explanation is that Copy types do not
/// implement the Drop trait, which means they have no destructors. Without a
/// destructor, there is nothing for `core::mem::forget` to ignore.
pub FORGETTING_COPY_TYPES,
Warn,
"calls to `core::mem::forget` with a value that implements Copy"
}
declare_lint! {
/// The `undropped_manually_drops` lint check for calls to `core::mem::drop`
/// and `core::ptr::drop_in_place` where the dropped value is `core::mem::ManuallyDrop`
/// which doesn't drop.
///
/// ### Example
///
/// ```rust,compile_fail
/// struct S;
/// drop(core::mem::ManuallyDrop::new(S));
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `ManuallyDrop` does not drop it's inner value so calling `core::mem::drop` will
/// not drop the inner value of the `ManuallyDrop` either.
pub UNDROPPED_MANUALLY_DROPS,
Deny,
"calls to `drop` and `drop_in_place` where the dropped value is `core::mem::ManuallyDrop`"
}
declare_lint_pass!(DropForgetUseless => [DROPPING_REFERENCES, FORGETTING_REFERENCES, DROPPING_COPY_TYPES, FORGETTING_COPY_TYPES, UNDROPPED_MANUALLY_DROPS]);
impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
let (fn_did, arg) = match expr.kind {
// matching on `function(<receiver>, ...)`
ExprKind::Call(path, [arg]) if let ExprKind::Path(ref qpath) = path.kind => {
(cx.qpath_res(qpath, path.hir_id).opt_def_id(), arg)
}
// matching on `<receiver>.method(..)`
ExprKind::MethodCall(_, arg, _, _) => {
(cx.typeck_results().type_dependent_def_id(expr.hir_id), arg)
}
_ => return,
};
if let Some(fn_did) = fn_did
&& let Some(fn_name) = cx.tcx.get_diagnostic_name(fn_did)
{
let arg_ty = cx.typeck_results().expr_ty(arg);
let is_copy = cx.type_is_copy_modulo_regions(arg_ty);
let drop_is_single_call_in_arm = is_single_call_in_arm(cx, arg, expr);
let let_underscore_ignore_sugg = || {
if let Some((_, node)) = cx.tcx.hir_parent_iter(expr.hir_id).nth(0)
&& let Node::Stmt(stmt) = node
&& let StmtKind::Semi(e) = stmt.kind
&& e.hir_id == expr.hir_id
&& let Some(arg_span) = arg.span.find_ancestor_inside_same_ctxt(expr.span)
{
UseLetUnderscoreIgnoreSuggestion::Suggestion {
start_span: expr.span.shrink_to_lo().until(arg_span),
end_span: arg_span.shrink_to_hi().until(expr.span.shrink_to_hi()),
}
} else {
UseLetUnderscoreIgnoreSuggestion::Note
}
};
match fn_name {
sym::mem_drop if arg_ty.is_ref() && !drop_is_single_call_in_arm => {
cx.emit_span_lint(
DROPPING_REFERENCES,
expr.span,
DropRefDiag { arg_ty, label: arg.span, sugg: let_underscore_ignore_sugg() },
);
}
sym::ptr_drop_in_place | sym::ptr_drop_in_place_self
if let &ty::RawPtr(inner_ty, _mutbl) = arg_ty.kind()
&& inner_ty.is_ref()
&& !drop_is_single_call_in_arm =>
{
cx.emit_span_lint(
DROPPING_REFERENCES,
expr.span,
DropInPlaceRefDiag {
arg_ty,
label: arg.span,
sugg: let_underscore_ignore_sugg(),
from_fn: fn_name == sym::ptr_drop_in_place,
},
);
}
sym::mem_forget if arg_ty.is_ref() => {
cx.emit_span_lint(
FORGETTING_REFERENCES,
expr.span,
ForgetRefDiag {
arg_ty,
label: arg.span,
sugg: let_underscore_ignore_sugg(),
},
);
}
sym::mem_drop if is_copy && !drop_is_single_call_in_arm => {
cx.emit_span_lint(
DROPPING_COPY_TYPES,
expr.span,
DropCopyDiag {
arg_ty,
label: arg.span,
sugg: let_underscore_ignore_sugg(),
},
);
}
sym::ptr_drop_in_place | sym::ptr_drop_in_place_self
if let &ty::RawPtr(inner_ty, _mutbl) = arg_ty.kind()
&& cx.type_is_copy_modulo_regions(inner_ty)
&& !drop_is_single_call_in_arm =>
{
cx.emit_span_lint(
DROPPING_COPY_TYPES,
expr.span,
DropInPlaceCopyDiag {
arg_ty,
label: arg.span,
sugg: let_underscore_ignore_sugg(),
from_fn: fn_name == sym::ptr_drop_in_place,
},
);
}
sym::mem_forget if is_copy => {
cx.emit_span_lint(
FORGETTING_COPY_TYPES,
expr.span,
ForgetCopyDiag {
arg_ty,
label: arg.span,
sugg: let_underscore_ignore_sugg(),
},
);
}
sym::mem_drop
if let ty::Adt(adt, _) = arg_ty.kind()
&& adt.is_manually_drop() =>
{
cx.emit_span_lint(
UNDROPPED_MANUALLY_DROPS,
expr.span,
UndroppedManuallyDropsDiag {
arg_ty,
label: arg.span,
suggestion: UndroppedManuallyDropsSuggestion {
start_span: arg.span.shrink_to_lo(),
end_span: arg.span.shrink_to_hi(),
},
},
);
}
sym::ptr_drop_in_place | sym::ptr_drop_in_place_self
if let &ty::RawPtr(inner_ty, _mutbl) = arg_ty.kind()
&& let ty::Adt(adt, _) = inner_ty.kind()
&& adt.is_manually_drop() =>
{
cx.emit_span_lint(
UNDROPPED_MANUALLY_DROPS,
expr.span,
UndroppedManuallyDropsInPlaceDiag {
arg_ty,
label: arg.span,
suggestion: UndroppedManuallyDropsInPlaceSuggestion {
start_span: expr.span.shrink_to_lo().until(arg.span.shrink_to_lo()),
end_span: arg.span.shrink_to_hi().until(expr.span.shrink_to_hi()),
},
},
);
}
_ => return,
};
}
}
}
// Dropping returned value of a function, as in the following snippet is considered idiomatic, see
// rust-lang/rust-clippy#9482 for examples.
//
// ```
// match <var> {
// <pat> => drop(fn_with_side_effect_and_returning_some_value()),
// ..
// }
// ```
fn is_single_call_in_arm<'tcx>(
cx: &LateContext<'tcx>,
arg: &'tcx Expr<'_>,
drop_expr: &'tcx Expr<'_>,
) -> bool {
if arg.can_have_side_effects() {
if let Node::Arm(Arm { body, .. }) = cx.tcx.parent_hir_node(drop_expr.hir_id) {
return body.hir_id == drop_expr.hir_id;
}
}
false
}