rust-clippy/clippy_lints/src/mem_replace.rs

265 lines
9.7 KiB
Rust
Raw Normal View History

use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg, span_lint_and_then};
use clippy_utils::source::{snippet, snippet_with_applicability};
use clippy_utils::ty::is_non_aggregate_primitive_type;
use clippy_utils::{is_default_equivalent, is_lang_ctor, meets_msrv, msrvs};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::OptionNone;
2020-01-06 16:39:50 +00:00
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
2021-12-04 15:09:15 +00:00
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::lint::in_external_macro;
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Span;
use rustc_span::symbol::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for `mem::replace()` on an `Option` with
/// `None`.
///
/// ### Why is this bad?
/// `Option` already has the method `take()` for
/// taking its current value (Some(..) or None) and replacing it with
/// `None`.
///
/// ### Example
/// ```rust
2019-03-05 22:23:50 +00:00
/// use std::mem;
///
/// let mut an_option = Some(0);
/// let replaced = mem::replace(&mut an_option, None);
/// ```
/// Is better expressed with:
/// ```rust
/// let mut an_option = Some(0);
/// let taken = an_option.take();
/// ```
#[clippy::version = "1.31.0"]
pub MEM_REPLACE_OPTION_WITH_NONE,
style,
"replacing an `Option` with `None` instead of `take()`"
}
2019-09-13 16:39:14 +00:00
declare_clippy_lint! {
/// ### What it does
/// Checks for `mem::replace(&mut _, mem::uninitialized())`
2019-09-13 16:39:14 +00:00
/// and `mem::replace(&mut _, mem::zeroed())`.
///
/// ### Why is this bad?
/// This will lead to undefined behavior even if the
2019-09-13 16:39:14 +00:00
/// value is overwritten later, because the uninitialized value may be
/// observed in the case of a panic.
///
/// ### Example
2019-09-13 16:39:14 +00:00
/// ```
/// use std::mem;
///# fn may_panic(v: Vec<i32>) -> Vec<i32> { v }
///
/// #[allow(deprecated, invalid_value)]
/// fn myfunc (v: &mut Vec<i32>) {
/// let taken_v = unsafe { mem::replace(v, mem::uninitialized()) };
/// let new_v = may_panic(taken_v); // undefined behavior on panic
/// mem::forget(mem::replace(v, new_v));
/// }
/// ```
///
/// The [take_mut](https://docs.rs/take_mut) crate offers a sound solution,
/// at the cost of either lazily creating a replacement value or aborting
/// on panic, to ensure that the uninitialized value cannot be observed.
#[clippy::version = "1.39.0"]
2019-09-13 16:39:14 +00:00
pub MEM_REPLACE_WITH_UNINIT,
correctness,
"`mem::replace(&mut _, mem::uninitialized())` or `mem::replace(&mut _, mem::zeroed())`"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for `std::mem::replace` on a value of type
/// `T` with `T::default()`.
///
/// ### Why is this bad?
/// `std::mem` module already has the method `take` to
/// take the current value and replace it with the default value of that type.
///
/// ### Example
/// ```rust
/// let mut text = String::from("foo");
/// let replaced = std::mem::replace(&mut text, String::default());
/// ```
/// Is better expressed with:
/// ```rust
/// let mut text = String::from("foo");
/// let taken = std::mem::take(&mut text);
/// ```
#[clippy::version = "1.42.0"]
pub MEM_REPLACE_WITH_DEFAULT,
style,
"replacing a value of type `T` with `T::default()` instead of using `std::mem::take`"
}
impl_lint_pass!(MemReplace =>
[MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]);
fn check_replace_option_with_none(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
2019-12-22 19:05:19 +00:00
if let ExprKind::Path(ref replacement_qpath) = src.kind {
// Check that second argument is `Option::None`
if is_lang_ctor(cx, replacement_qpath, OptionNone) {
// Since this is a late pass (already type-checked),
// and we already know that the second argument is an
// `Option`, we do not need to check the first
// argument's type. All that's left is to get
// replacee's path.
2019-12-22 19:05:19 +00:00
let replaced_path = match dest.kind {
ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, replaced) => {
if let ExprKind::Path(QPath::Resolved(None, replaced_path)) = replaced.kind {
replaced_path
} else {
return;
}
},
ExprKind::Path(QPath::Resolved(None, replaced_path)) => replaced_path,
_ => return,
};
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_OPTION_WITH_NONE,
2019-12-22 19:05:19 +00:00
expr_span,
"replacing an `Option` with `None`",
"consider `Option::take()` instead",
format!(
"{}.take()",
snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)
),
applicability,
);
}
}
}
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()
2020-07-17 08:47:04 +00:00
if let Some(method_def_id) = cx.typeck_results().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(repl_func, 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.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) &&
2020-07-17 08:47:04 +00:00
!cx.typeck_results().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_default(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
// disable lint for primitives
let expr_type = cx.typeck_results().expr_ty_adjusted(src);
if is_non_aggregate_primitive_type(expr_type) {
return;
}
// disable lint for Option since it is covered in another lint
if let ExprKind::Path(q) = &src.kind {
if is_lang_ctor(cx, q, OptionNone) {
return;
}
}
if is_default_equivalent(cx, src) && !in_external_macro(cx.tcx.sess, expr_span) {
span_lint_and_then(
cx,
MEM_REPLACE_WITH_DEFAULT,
expr_span,
"replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
|diag| {
if !expr_span.from_expansion() {
let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
diag.span_suggestion(
expr_span,
"consider using",
suggestion,
Applicability::MachineApplicable,
);
}
},
);
}
}
pub struct MemReplace {
msrv: Option<RustcVersion>,
}
impl MemReplace {
#[must_use]
pub fn new(msrv: Option<RustcVersion>) -> Self {
Self { msrv }
}
}
impl<'tcx> LateLintPass<'tcx> for MemReplace {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
2018-09-18 23:54:01 +00:00
// Check that `expr` is a call to `mem::replace()`
if let ExprKind::Call(func, func_args) = expr.kind;
2019-09-27 15:16:06 +00:00
if let ExprKind::Path(ref func_qpath) = func.kind;
if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
if cx.tcx.is_diagnostic_item(sym::mem_replace, def_id);
if let [dest, src] = func_args;
then {
2019-12-22 19:05:19 +00:00
check_replace_option_with_none(cx, src, dest, expr.span);
check_replace_with_uninit(cx, src, dest, expr.span);
2022-05-08 11:13:14 +00:00
if meets_msrv(self.msrv, msrvs::MEM_TAKE) {
check_replace_with_default(cx, src, dest, expr.span);
}
}
}
}
extract_msrv_attr!(LateContext);
}