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Lint needless_borrow on most union field accesses

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This commit is contained in:
Jason Newcomb 2023-09-14 12:41:16 -04:00
parent 34b7d1559f
commit a68cd88860
4 changed files with 112 additions and 29 deletions
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21
clippy_lints/src/dereference.rs
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@ -5,6 +5,7 @@
use clippy_utils::{
expr_use_ctxt, get_parent_expr, get_parent_node, is_lint_allowed, path_to_local, DefinedTy, ExprUseNode,
};
use core::mem;
use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
use rustc_data_structures::fx::FxIndexMap;
use rustc_errors::Applicability;
@ -342,8 +343,24 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
TyCoercionStability::for_defined_ty(cx, ty, use_cx.node.is_return())
});
let can_auto_borrow = match use_cx.node {
ExprUseNode::Callee => true,
ExprUseNode::FieldAccess(_) => adjusted_ty.ty_adt_def().map_or(true, |adt| !adt.is_union()),
ExprUseNode::FieldAccess(_)
if !use_cx.moved_before_use && matches!(sub_expr.kind, ExprKind::Field(..)) =>
{
// `ManuallyDrop` fields of a union will not automatically call
// `deref_mut` when accessing a field.
// Note: if the `ManuallyDrop` value is not directly a field of a
// union then `DerefMut` will work as normal.
//
// This means we need to not modify an expression such as `(&mut x.y).z`
// if accessing `z` would require `DerefMut`.
let mut ty = expr_ty;
!use_cx.adjustments.iter().any(|a| {
let ty = mem::replace(&mut ty, a.target);
matches!(a.kind, Adjust::Deref(Some(ref op)) if op.mutbl == Mutability::Mut)
&& ty.ty_adt_def().map_or(false, |def| def.is_manually_drop())
})
},
ExprUseNode::Callee | ExprUseNode::FieldAccess(_) => true,
ExprUseNode::MethodArg(hir_id, _, 0) if !use_cx.moved_before_use => {
// Check for calls to trait methods where the trait is implemented
// on a reference.

47
tests/ui/needless_borrow.fixed
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@ -190,27 +190,48 @@ fn issue9383() {
// Should not lint because unions need explicit deref when accessing field
use std::mem::ManuallyDrop;
union Coral {
crab: ManuallyDrop<Vec<i32>>,
#[derive(Clone, Copy)]
struct Wrap<T>(T);
impl<T> core::ops::Deref for Wrap<T> {
type Target = T;
fn deref(&self) -> &T {
&self.0
}
}
impl<T> core::ops::DerefMut for Wrap<T> {
fn deref_mut(&mut self) -> &mut T {
&mut self.0
}
}
union Ocean {
coral: ManuallyDrop<Coral>,
union U<T: Copy> {
u: T,
}
let mut ocean = Ocean {
coral: ManuallyDrop::new(Coral {
crab: ManuallyDrop::new(vec![1, 2, 3]),
}),
};
#[derive(Clone, Copy)]
struct Foo {
x: u32,
}
unsafe {
ManuallyDrop::drop(&mut (&mut ocean.coral).crab);
let mut x = U {
u: ManuallyDrop::new(Foo { x: 0 }),
};
let _ = &mut (&mut x.u).x;
let _ = &mut { x.u }.x;
let _ = &mut ({ &mut x.u }).x;
(*ocean.coral).crab = ManuallyDrop::new(vec![4, 5, 6]);
ManuallyDrop::drop(&mut (*ocean.coral).crab);
let mut x = U {
u: Wrap(ManuallyDrop::new(Foo { x: 0 })),
};
let _ = &mut (&mut x.u).x;
let _ = &mut { x.u }.x;
let _ = &mut ({ &mut x.u }).x;
ManuallyDrop::drop(&mut ocean.coral);
let mut x = U { u: Wrap(Foo { x: 0 }) };
let _ = &mut x.u.x;
let _ = &mut { x.u }.x;
let _ = &mut ({ &mut x.u }).x;
}
}

47
tests/ui/needless_borrow.rs
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@ -190,27 +190,48 @@ fn issue9383() {
// Should not lint because unions need explicit deref when accessing field
use std::mem::ManuallyDrop;
union Coral {
crab: ManuallyDrop<Vec<i32>>,
#[derive(Clone, Copy)]
struct Wrap<T>(T);
impl<T> core::ops::Deref for Wrap<T> {
type Target = T;
fn deref(&self) -> &T {
&self.0
}
}
impl<T> core::ops::DerefMut for Wrap<T> {
fn deref_mut(&mut self) -> &mut T {
&mut self.0
}
}
union Ocean {
coral: ManuallyDrop<Coral>,
union U<T: Copy> {
u: T,
}
let mut ocean = Ocean {
coral: ManuallyDrop::new(Coral {
crab: ManuallyDrop::new(vec![1, 2, 3]),
}),
};
#[derive(Clone, Copy)]
struct Foo {
x: u32,
}
unsafe {
ManuallyDrop::drop(&mut (&mut ocean.coral).crab);
let mut x = U {
u: ManuallyDrop::new(Foo { x: 0 }),
};
let _ = &mut (&mut x.u).x;
let _ = &mut (&mut { x.u }).x;
let _ = &mut ({ &mut x.u }).x;
(*ocean.coral).crab = ManuallyDrop::new(vec![4, 5, 6]);
ManuallyDrop::drop(&mut (*ocean.coral).crab);
let mut x = U {
u: Wrap(ManuallyDrop::new(Foo { x: 0 })),
};
let _ = &mut (&mut x.u).x;
let _ = &mut (&mut { x.u }).x;
let _ = &mut ({ &mut x.u }).x;
ManuallyDrop::drop(&mut ocean.coral);
let mut x = U { u: Wrap(Foo { x: 0 }) };
let _ = &mut (&mut x.u).x;
let _ = &mut (&mut { x.u }).x;
let _ = &mut ({ &mut x.u }).x;
}
}

26
tests/ui/needless_borrow.stderr
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@ -133,5 +133,29 @@ error: this expression borrows a value the compiler would automatically borrow
LL | (&mut self.f)()
| ^^^^^^^^^^^^^ help: change this to: `(self.f)`
error: aborting due to 22 previous errors
error: this expression borrows a value the compiler would automatically borrow
--> $DIR/needless_borrow.rs:221:22
|
LL | let _ = &mut (&mut { x.u }).x;
| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
error: this expression borrows a value the compiler would automatically borrow
--> $DIR/needless_borrow.rs:228:22
|
LL | let _ = &mut (&mut { x.u }).x;
| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
error: this expression borrows a value the compiler would automatically borrow
--> $DIR/needless_borrow.rs:232:22
|
LL | let _ = &mut (&mut x.u).x;
| ^^^^^^^^^^ help: change this to: `x.u`
error: this expression borrows a value the compiler would automatically borrow
--> $DIR/needless_borrow.rs:233:22
|
LL | let _ = &mut (&mut { x.u }).x;
| ^^^^^^^^^^^^^^ help: change this to: `{ x.u }`
error: aborting due to 26 previous errors