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|
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::{implements_trait, is_must_use_ty, match_type};
use clippy_utils::{is_must_use_func_call, paths};
use rustc_hir::{Local, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_session::{declare_lint_pass, declare_tool_lint};
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
///
/// ### Example
/// ```rust
/// fn f() -> Result<u32, u32> {
/// Ok(0)
/// }
///
/// let _ = f();
/// // 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`. This supports `mutex` and `rwlock` in
/// `parking_lot`. For `std` locks see the `rustc` lint
/// [`let_underscore_lock`](https://doc.rust-lang.org/nightly/rustc/lints/listing/deny-by-default.html#let-underscore-lock)
///
/// ### 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.
///
/// ### Example
/// ```rust,ignore
/// let _ = mutex.lock();
/// ```
///
/// 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_clippy_lint! {
/// ### What it does
/// Checks for `let _ = <expr>` where the resulting type of expr implements `Future`
///
/// ### Why is this bad?
/// Futures must be polled for work to be done. The original intention was most likely to await the future
/// and ignore the resulting value.
///
/// ### Example
/// ```rust
/// async fn foo() -> Result<(), ()> {
/// Ok(())
/// }
/// let _ = foo();
/// ```
///
/// Use instead:
/// ```rust
/// # async fn context() {
/// async fn foo() -> Result<(), ()> {
/// Ok(())
/// }
/// let _ = foo().await;
/// # }
/// ```
#[clippy::version = "1.67.0"]
pub LET_UNDERSCORE_FUTURE,
suspicious,
"non-binding `let` on a future"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for `let _ = <expr>` without a type annotation, and suggests to either provide one,
/// or remove the `let` keyword altogether.
///
/// ### Why is this bad?
/// The `let _ = <expr>` expression ignores the value of `<expr>` but will remain doing so even
/// if the type were to change, thus potentially introducing subtle bugs. By supplying a type
/// annotation, one will be forced to re-visit the decision to ignore the value in such cases.
///
/// ### Known problems
/// The `_ = <expr>` is not properly supported by some tools (e.g. IntelliJ) and may seem odd
/// to many developers. This lint also partially overlaps with the other `let_underscore_*`
/// lints.
///
/// ### Example
/// ```rust
/// fn foo() -> Result<u32, ()> {
/// Ok(123)
/// }
/// let _ = foo();
/// ```
/// Use instead:
/// ```rust
/// fn foo() -> Result<u32, ()> {
/// Ok(123)
/// }
/// // Either provide a type annotation:
/// let _: Result<u32, ()> = foo();
/// // …or drop the let keyword:
/// _ = foo();
/// ```
#[clippy::version = "1.69.0"]
pub LET_UNDERSCORE_UNTYPED,
pedantic,
"non-binding `let` without a type annotation"
}
declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK, LET_UNDERSCORE_FUTURE, LET_UNDERSCORE_UNTYPED]);
const SYNC_GUARD_PATHS: [&[&str]; 3] = [
&paths::PARKING_LOT_MUTEX_GUARD,
&paths::PARKING_LOT_RWLOCK_READ_GUARD,
&paths::PARKING_LOT_RWLOCK_WRITE_GUARD,
];
impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
if !in_external_macro(cx.tcx.sess, local.span)
&& let PatKind::Wild = local.pat.kind
&& let Some(init) = local.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)),
GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
});
if contains_sync_guard {
span_lint_and_help(
cx,
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 let Some(future_trait_def_id) = cx.tcx.lang_items().future_trait()
&& implements_trait(cx, cx.typeck_results().expr_ty(init), future_trait_def_id, &[]) {
span_lint_and_help(
cx,
LET_UNDERSCORE_FUTURE,
local.span,
"non-binding `let` on a future",
None,
"consider awaiting the future or dropping explicitly with `std::mem::drop`"
);
} 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",
);
}
if local.pat.default_binding_modes && local.ty.is_none() {
// When `default_binding_modes` is true, the `let` keyword is present.
span_lint_and_help(
cx,
LET_UNDERSCORE_UNTYPED,
local.span,
"non-binding `let` without a type annotation",
None,
"consider adding a type annotation or removing the `let` keyword",
);
}
}
}
}
|
