rust-clippy/clippy_lints/src/await_holding_invalid.rs

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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::{match_def_path, paths};
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::def_id::DefId;
use rustc_hir::{def::Res, AsyncGeneratorKind, Body, BodyId, GeneratorKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::GeneratorInteriorTypeCause;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::Span;
use crate::utils::conf::DisallowedType;
declare_clippy_lint! {
/// ### What it does
/// Checks for calls to await while holding a non-async-aware MutexGuard.
///
/// ### Why is this bad?
/// The Mutex types found in std::sync and parking_lot
/// are not designed to operate in an async context across await points.
///
/// There are two potential solutions. One is to use an async-aware Mutex
/// type. Many asynchronous foundation crates provide such a Mutex type. The
/// other solution is to ensure the mutex is unlocked before calling await,
/// either by introducing a scope or an explicit call to Drop::drop.
///
/// ### Known problems
/// Will report false positive for explicitly dropped guards
/// ([#6446](https://github.com/rust-lang/rust-clippy/issues/6446)). A workaround for this is
/// to wrap the `.lock()` call in a block instead of explicitly dropping the guard.
///
/// ### Example
/// ```rust
/// # use std::sync::Mutex;
/// # async fn baz() {}
/// async fn foo(x: &Mutex<u32>) {
/// let mut guard = x.lock().unwrap();
/// *guard += 1;
/// baz().await;
/// }
///
/// async fn bar(x: &Mutex<u32>) {
/// let mut guard = x.lock().unwrap();
/// *guard += 1;
/// drop(guard); // explicit drop
/// baz().await;
/// }
/// ```
///
/// Use instead:
/// ```rust
/// # use std::sync::Mutex;
/// # async fn baz() {}
/// async fn foo(x: &Mutex<u32>) {
/// {
/// let mut guard = x.lock().unwrap();
/// *guard += 1;
/// }
/// baz().await;
/// }
///
/// async fn bar(x: &Mutex<u32>) {
/// {
/// let mut guard = x.lock().unwrap();
/// *guard += 1;
/// } // guard dropped here at end of scope
/// baz().await;
/// }
/// ```
#[clippy::version = "1.45.0"]
pub AWAIT_HOLDING_LOCK,
suspicious,
"inside an async function, holding a `MutexGuard` while calling `await`"
}
declare_clippy_lint! {
/// ### What it does
/// Checks for calls to await while holding a `RefCell` `Ref` or `RefMut`.
///
/// ### Why is this bad?
/// `RefCell` refs only check for exclusive mutable access
/// at runtime. Holding onto a `RefCell` ref across an `await` suspension point
/// risks panics from a mutable ref shared while other refs are outstanding.
///
/// ### Known problems
/// Will report false positive for explicitly dropped refs
/// ([#6353](https://github.com/rust-lang/rust-clippy/issues/6353)). A workaround for this is
/// to wrap the `.borrow[_mut]()` call in a block instead of explicitly dropping the ref.
///
/// ### Example
/// ```rust
/// # use std::cell::RefCell;
/// # async fn baz() {}
/// async fn foo(x: &RefCell<u32>) {
/// let mut y = x.borrow_mut();
/// *y += 1;
/// baz().await;
/// }
///
/// async fn bar(x: &RefCell<u32>) {
/// let mut y = x.borrow_mut();
/// *y += 1;
/// drop(y); // explicit drop
/// baz().await;
/// }
/// ```
///
/// Use instead:
/// ```rust
/// # use std::cell::RefCell;
/// # async fn baz() {}
/// async fn foo(x: &RefCell<u32>) {
/// {
/// let mut y = x.borrow_mut();
/// *y += 1;
/// }
/// baz().await;
/// }
///
/// async fn bar(x: &RefCell<u32>) {
/// {
/// let mut y = x.borrow_mut();
/// *y += 1;
/// } // y dropped here at end of scope
/// baz().await;
/// }
/// ```
#[clippy::version = "1.49.0"]
pub AWAIT_HOLDING_REFCELL_REF,
suspicious,
"inside an async function, holding a `RefCell` ref while calling `await`"
}
declare_clippy_lint! {
/// ### What it does
/// Allows users to configure types which should not be held across `await`
/// suspension points.
///
/// ### Why is this bad?
/// There are some types which are perfectly "safe" to be used concurrently
/// from a memory access perspective but will cause bugs at runtime if they
/// are held in such a way.
///
/// ### Known problems
///
/// ### Example
///
/// Strings are, of course, safe to hold across await points. This example
/// exists only to show how this lint might be configured for third-party
/// crates.
///
/// ```toml
/// await-holding-invalid-types = [
/// "std::string::String",
/// ]
/// ```
///
/// ```rust
/// # async fn baz() {}
/// async fn foo() {
/// let _x = String::from("hello!");
/// baz().await; // Lint violation
/// }
/// ```
#[clippy::version = "1.49.0"]
pub AWAIT_HOLDING_INVALID_TYPE,
suspicious,
"holding a type across an await point which is not allowed to be held as per the configuration"
}
impl_lint_pass!(AwaitHolding => [AWAIT_HOLDING_LOCK, AWAIT_HOLDING_REFCELL_REF, AWAIT_HOLDING_INVALID_TYPE]);
#[derive(Debug)]
pub struct AwaitHolding {
conf_invalid_types: Vec<DisallowedType>,
def_ids: FxHashMap<DefId, DisallowedType>,
}
impl AwaitHolding {
pub(crate) fn new(conf_invalid_types: Vec<DisallowedType>) -> Self {
Self {
conf_invalid_types,
def_ids: FxHashMap::default(),
}
}
}
impl LateLintPass<'_> for AwaitHolding {
fn check_crate(&mut self, cx: &LateContext<'_>) {
for conf in &self.conf_invalid_types {
let path = match conf {
DisallowedType::Simple(path) | DisallowedType::WithReason { path, .. } => path,
};
let segs: Vec<_> = path.split("::").collect();
if let Res::Def(_, id) = clippy_utils::def_path_res(cx, &segs) {
self.def_ids.insert(id, conf.clone());
}
}
}
fn check_body(&mut self, cx: &LateContext<'_>, body: &'_ Body<'_>) {
use AsyncGeneratorKind::{Block, Closure, Fn};
if let Some(GeneratorKind::Async(Block | Closure | Fn)) = body.generator_kind {
let body_id = BodyId {
hir_id: body.value.hir_id,
};
let typeck_results = cx.tcx.typeck_body(body_id);
self.check_interior_types(
cx,
typeck_results.generator_interior_types.as_ref().skip_binder(),
body.value.span,
);
}
}
}
impl AwaitHolding {
fn check_interior_types(&self, cx: &LateContext<'_>, ty_causes: &[GeneratorInteriorTypeCause<'_>], span: Span) {
for ty_cause in ty_causes {
if let rustc_middle::ty::Adt(adt, _) = ty_cause.ty.kind() {
if is_mutex_guard(cx, adt.did()) {
span_lint_and_then(
cx,
AWAIT_HOLDING_LOCK,
ty_cause.span,
"this `MutexGuard` is held across an `await` point",
|diag| {
diag.help(
"consider using an async-aware `Mutex` type or ensuring the \
`MutexGuard` is dropped before calling await",
);
diag.span_note(
ty_cause.scope_span.unwrap_or(span),
"these are all the `await` points this lock is held through",
);
},
);
} else if is_refcell_ref(cx, adt.did()) {
span_lint_and_then(
cx,
AWAIT_HOLDING_REFCELL_REF,
ty_cause.span,
"this `RefCell` reference is held across an `await` point",
|diag| {
diag.help("ensure the reference is dropped before calling `await`");
diag.span_note(
ty_cause.scope_span.unwrap_or(span),
"these are all the `await` points this reference is held through",
);
},
);
} else if let Some(disallowed) = self.def_ids.get(&adt.did()) {
emit_invalid_type(cx, ty_cause.span, disallowed);
}
}
}
}
}
fn emit_invalid_type(cx: &LateContext<'_>, span: Span, disallowed: &DisallowedType) {
let (type_name, reason) = match disallowed {
DisallowedType::Simple(path) => (path, &None),
DisallowedType::WithReason { path, reason } => (path, reason),
};
span_lint_and_then(
cx,
AWAIT_HOLDING_INVALID_TYPE,
span,
&format!("`{type_name}` may not be held across an `await` point according to config",),
|diag| {
if let Some(reason) = reason {
diag.note(format!("{reason} (according to clippy.toml)"));
}
},
);
}
fn is_mutex_guard(cx: &LateContext<'_>, def_id: DefId) -> bool {
match_def_path(cx, def_id, &paths::MUTEX_GUARD)
|| match_def_path(cx, def_id, &paths::RWLOCK_READ_GUARD)
|| match_def_path(cx, def_id, &paths::RWLOCK_WRITE_GUARD)
|| match_def_path(cx, def_id, &paths::PARKING_LOT_MUTEX_GUARD)
|| match_def_path(cx, def_id, &paths::PARKING_LOT_RWLOCK_READ_GUARD)
|| match_def_path(cx, def_id, &paths::PARKING_LOT_RWLOCK_WRITE_GUARD)
}
fn is_refcell_ref(cx: &LateContext<'_>, def_id: DefId) -> bool {
match_def_path(cx, def_id, &paths::REFCELL_REF) || match_def_path(cx, def_id, &paths::REFCELL_REFMUT)
}