+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::ty::{is_must_use_ty, match_type};
+use clippy_utils::{is_must_use_func_call, paths};
use if_chain::if_chain;
use rustc_hir::{Local, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::subst::GenericArgKind;
use rustc_session::{declare_lint_pass, declare_tool_lint};
-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>`
- /// where expr is #[must_use]
- ///
- /// **Why is this bad?** It's better to explicitly
- /// handle the value of a #[must_use] expr
+ /// ### What it does
+ /// Checks for `let _ = <expr>` where expr is `#[must_use]`
///
- /// **Known problems:** None.
+ /// ### Why is this bad?
+ /// It's better to explicitly handle the value of a `#[must_use]`
+ /// expr
///
- /// **Example:**
+ /// ### Example
/// ```rust
/// fn f() -> Result<u32, u32> {
/// Ok(0)
/// // is_ok() is marked #[must_use]
/// let _ = f().is_ok();
/// ```
+ #[clippy::version = "1.42.0"]
pub LET_UNDERSCORE_MUST_USE,
restriction,
"non-binding let on a `#[must_use]` expression"
}
declare_clippy_lint! {
- /// **What it does:** Checks for `let _ = sync_lock`
+ /// ### What it does
+ /// Checks for `let _ = sync_lock`.
+ /// This supports `mutex` and `rwlock` in `std::sync` and `parking_lot`.
///
- /// **Why is this bad?** This statement immediately drops the lock instead of
- /// extending it's lifetime to the end of the scope, which is often not intended.
+ /// ### Why is this bad?
+ /// This statement immediately drops the lock instead of
+ /// extending its lifetime to the end of the scope, which is often not intended.
/// To extend lock lifetime to the end of the scope, use an underscore-prefixed
/// name instead (i.e. _lock). If you want to explicitly drop the lock,
/// `std::mem::drop` conveys your intention better and is less error-prone.
///
- /// **Known problems:** None.
- ///
- /// **Example:**
- ///
- /// Bad:
+ /// ### Example
/// ```rust,ignore
/// let _ = mutex.lock();
/// ```
///
- /// Good:
+ /// Use instead:
/// ```rust,ignore
/// let _lock = mutex.lock();
/// ```
+ #[clippy::version = "1.43.0"]
pub LET_UNDERSCORE_LOCK,
correctness,
"non-binding let on a synchronization lock"
}
-declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK]);
+declare_clippy_lint! {
+ /// ### What it does
+ /// Checks for `let _ = <expr>`
+ /// where expr has a type that implements `Drop`
+ ///
+ /// ### Why is this bad?
+ /// This statement immediately drops the initializer
+ /// expression instead of extending its lifetime to the end of the scope, which
+ /// is often not intended. To extend the expression's lifetime to the end of the
+ /// scope, use an underscore-prefixed name instead (i.e. _var). If you want to
+ /// explicitly drop the expression, `std::mem::drop` conveys your intention
+ /// better and is less error-prone.
+ ///
+ /// ### Example
+ /// ```rust
+ /// # struct DroppableItem;
+ /// {
+ /// let _ = DroppableItem;
+ /// // ^ dropped here
+ /// /* more code */
+ /// }
+ /// ```
+ ///
+ /// Use instead:
+ /// ```rust
+ /// # struct DroppableItem;
+ /// {
+ /// let _droppable = DroppableItem;
+ /// /* more code */
+ /// // dropped at end of scope
+ /// }
+ /// ```
+ #[clippy::version = "1.50.0"]
+ pub LET_UNDERSCORE_DROP,
+ pedantic,
+ "non-binding let on a type that implements `Drop`"
+}
+
+declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK, LET_UNDERSCORE_DROP]);
-const SYNC_GUARD_PATHS: [&[&str]; 3] = [
+const SYNC_GUARD_PATHS: [&[&str]; 6] = [
&paths::MUTEX_GUARD,
&paths::RWLOCK_READ_GUARD,
&paths::RWLOCK_WRITE_GUARD,
+ &paths::PARKING_LOT_MUTEX_GUARD,
+ &paths::PARKING_LOT_RWLOCK_READ_GUARD,
+ &paths::PARKING_LOT_RWLOCK_WRITE_GUARD,
];
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore {
- fn check_local(&mut self, cx: &LateContext<'_, '_>, local: &Local<'_>) {
+impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
+ fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
if in_external_macro(cx.tcx.sess, local.span) {
return;
}
if_chain! {
if let PatKind::Wild = local.pat.kind;
- if let Some(ref init) = local.init;
+ if let Some(init) = local.init;
then {
- let init_ty = cx.tables.expr_ty(init);
+ let init_ty = cx.typeck_results().expr_ty(init);
let contains_sync_guard = init_ty.walk().any(|inner| match inner.unpack() {
GenericArgKind::Type(inner_ty) => {
SYNC_GUARD_PATHS.iter().any(|path| match_type(cx, inner_ty, path))
LET_UNDERSCORE_LOCK,
local.span,
"non-binding let on a synchronization lock",
+ None,
+ "consider using an underscore-prefixed named \
+ binding or dropping explicitly with `std::mem::drop`"
+ );
+ } else if init_ty.needs_drop(cx.tcx, cx.param_env) {
+ span_lint_and_help(
+ cx,
+ LET_UNDERSCORE_DROP,
+ local.span,
+ "non-binding `let` on a type that implements `Drop`",
+ None,
"consider using an underscore-prefixed named \
binding or dropping explicitly with `std::mem::drop`"
- )
- } else if is_must_use_ty(cx, cx.tables.expr_ty(init)) {
+ );
+ } else if is_must_use_ty(cx, cx.typeck_results().expr_ty(init)) {
span_lint_and_help(
cx,
LET_UNDERSCORE_MUST_USE,
local.span,
"non-binding let on an expression with `#[must_use]` type",
+ None,
"consider explicitly using expression value"
- )
+ );
} else if is_must_use_func_call(cx, init) {
span_lint_and_help(
cx,
LET_UNDERSCORE_MUST_USE,
local.span,
"non-binding let on a result of a `#[must_use]` function",
+ None,
"consider explicitly using function result"
- )
+ );
}
}
}
projects / rust.git / blobdiff