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Auto merge of #5695 - esamudera:lint_mem_uninitialized, r=phansch
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New lint: suggest `ptr::read` instead of `mem::replace(..., uninitialized())`

resolves: #5575

changelog:
- add a new test case in `tests/ui/repl_uninit.rs` to cover the case of replacing with `mem::MaybeUninit::uninit().assume_init()`.
- modify the existing `MEM_REPLACE_WITH_UNINIT` when replacing with `mem::uninitialized` to suggest using `ptr::read` instead.
- lint with `MEM_REPLACE_WITH_UNINIT` when replacing with `mem::MaybeUninit::uninit().assume_init()`
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@bors
bors committed Jun 23, 2020
2 parents fa0f6a8 + 8c1ee06 commit c8484a1
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Showing 3 changed files with 71 additions and 36 deletions.
82 changes: 54 additions & 28 deletions clippy_lints/src/mem_replace.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -135,33 +135,59 @@ fn check_replace_option_with_none(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest
}
}

fn check_replace_with_uninit(cx: &LateContext<'_, '_>, src: &Expr<'_>, expr_span: Span) {
if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind {
if_chain! {
if repl_args.is_empty();
if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
then {
if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, repl_def_id) {
span_lint_and_help(
cx,
MEM_REPLACE_WITH_UNINIT,
expr_span,
"replacing with `mem::uninitialized()`",
None,
"consider using the `take_mut` crate instead",
);
} else if cx.tcx.is_diagnostic_item(sym::mem_zeroed, repl_def_id) &&
!cx.tables.expr_ty(src).is_primitive() {
span_lint_and_help(
cx,
MEM_REPLACE_WITH_UNINIT,
expr_span,
"replacing with `mem::zeroed()`",
None,
"consider using a default value or the `take_mut` crate instead",
);
}
fn check_replace_with_uninit(cx: &LateContext<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
if_chain! {
// check if replacement is mem::MaybeUninit::uninit().assume_init()
if let Some(method_def_id) = cx.tables.type_dependent_def_id(src.hir_id);
if cx.tcx.is_diagnostic_item(sym::assume_init, method_def_id);
then {
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_WITH_UNINIT,
expr_span,
"replacing with `mem::MaybeUninit::uninit().assume_init()`",
"consider using",
format!(
"std::ptr::read({})",
snippet_with_applicability(cx, dest.span, "", &mut applicability)
),
applicability,
);
return;
}
}

if_chain! {
if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind;
if repl_args.is_empty();
if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
then {
if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, repl_def_id) {
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_WITH_UNINIT,
expr_span,
"replacing with `mem::uninitialized()`",
"consider using",
format!(
"std::ptr::read({})",
snippet_with_applicability(cx, dest.span, "", &mut applicability)
),
applicability,
);
} else if cx.tcx.is_diagnostic_item(sym::mem_zeroed, repl_def_id) &&
!cx.tables.expr_ty(src).is_primitive() {
span_lint_and_help(
cx,
MEM_REPLACE_WITH_UNINIT,
expr_span,
"replacing with `mem::zeroed()`",
None,
"consider using a default value or the `take_mut` crate instead",
);
}
}
}
Expand Down Expand Up @@ -209,7 +235,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
if let [dest, src] = &**func_args;
then {
check_replace_option_with_none(cx, src, dest, expr.span);
check_replace_with_uninit(cx, src, expr.span);
check_replace_with_uninit(cx, src, dest, expr.span);
check_replace_with_default(cx, src, dest, expr.span);
}
}
Expand Down
6 changes: 6 additions & 0 deletions tests/ui/repl_uninit.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,12 @@ fn main() {
std::mem::forget(mem::replace(&mut v, new_v));
}

unsafe {
let taken_v = mem::replace(&mut v, mem::MaybeUninit::uninit().assume_init());
let new_v = might_panic(taken_v);
std::mem::forget(mem::replace(&mut v, new_v));
}

unsafe {
let taken_v = mem::replace(&mut v, mem::zeroed());
let new_v = might_panic(taken_v);
Expand Down
19 changes: 11 additions & 8 deletions tests/ui/repl_uninit.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,26 +2,29 @@ error: replacing with `mem::uninitialized()`
--> $DIR/repl_uninit.rs:15:23
|
LL | let taken_v = mem::replace(&mut v, mem::uninitialized());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::ptr::read(&mut v)`
|
= note: `-D clippy::mem-replace-with-uninit` implied by `-D warnings`
= help: consider using the `take_mut` crate instead

error: replacing with `mem::zeroed()`
error: replacing with `mem::MaybeUninit::uninit().assume_init()`
--> $DIR/repl_uninit.rs:21:23
|
LL | let taken_v = mem::replace(&mut v, mem::MaybeUninit::uninit().assume_init());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::ptr::read(&mut v)`

error: replacing with `mem::zeroed()`
--> $DIR/repl_uninit.rs:27:23
|
LL | let taken_v = mem::replace(&mut v, mem::zeroed());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using a default value or the `take_mut` crate instead

error: replacing with `mem::uninitialized()`
--> $DIR/repl_uninit.rs:33:28
--> $DIR/repl_uninit.rs:39:28
|
LL | let taken_u = unsafe { mem::replace(uref, mem::uninitialized()) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using the `take_mut` crate instead
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::ptr::read(uref)`

error: aborting due to 3 previous errors
error: aborting due to 4 previous errors

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