rust/tests/ui/significant_drop_in_scrutinee.rs

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// FIXME: Ideally these suggestions would be fixed via rustfix. Blocked by rust-lang/rust#53934
// // run-rustfix
#![warn(clippy::significant_drop_in_scrutinee)]
#![allow(dead_code, unused_assignments)]
#![allow(clippy::match_single_binding, clippy::single_match, clippy::uninlined_format_args)]
use std::num::ParseIntError;
use std::ops::Deref;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::RwLock;
use std::sync::{Mutex, MutexGuard};
struct State {}
impl State {
fn foo(&self) -> bool {
true
}
fn bar(&self) {}
}
fn should_not_trigger_lint_with_mutex_guard_outside_match() {
let mutex = Mutex::new(State {});
// Should not trigger lint because the temporary should drop at the `;` on line before the match
let is_foo = mutex.lock().unwrap().foo();
match is_foo {
true => {
mutex.lock().unwrap().bar();
},
false => {},
};
}
fn should_not_trigger_lint_with_mutex_guard_when_taking_ownership_in_match() {
let mutex = Mutex::new(State {});
// Should not trigger lint because the scrutinee is explicitly returning the MutexGuard,
// so its lifetime should not be surprising.
match mutex.lock() {
Ok(guard) => {
guard.foo();
mutex.lock().unwrap().bar();
},
_ => {},
};
}
fn should_trigger_lint_with_mutex_guard_in_match_scrutinee() {
let mutex = Mutex::new(State {});
// Should trigger lint because the lifetime of the temporary MutexGuard is surprising because it
// is preserved until the end of the match, but there is no clear indication that this is the
// case.
match mutex.lock().unwrap().foo() {
true => {
mutex.lock().unwrap().bar();
},
false => {},
};
}
fn should_not_trigger_lint_with_mutex_guard_in_match_scrutinee_when_lint_allowed() {
let mutex = Mutex::new(State {});
// Lint should not be triggered because it is "allowed" below.
#[allow(clippy::significant_drop_in_scrutinee)]
match mutex.lock().unwrap().foo() {
true => {
mutex.lock().unwrap().bar();
},
false => {},
};
}
fn should_not_trigger_lint_for_insignificant_drop() {
// Should not trigger lint because there are no temporaries whose drops have a significant
// side effect.
match 1u64.to_string().is_empty() {
true => {
println!("It was empty")
},
false => {
println!("It was not empty")
},
}
}
struct StateWithMutex {
m: Mutex<u64>,
}
struct MutexGuardWrapper<'a> {
mg: MutexGuard<'a, u64>,
}
impl<'a> MutexGuardWrapper<'a> {
fn get_the_value(&self) -> u64 {
*self.mg.deref()
}
}
struct MutexGuardWrapperWrapper<'a> {
mg: MutexGuardWrapper<'a>,
}
impl<'a> MutexGuardWrapperWrapper<'a> {
fn get_the_value(&self) -> u64 {
*self.mg.mg.deref()
}
}
impl StateWithMutex {
fn lock_m(&self) -> MutexGuardWrapper<'_> {
MutexGuardWrapper {
mg: self.m.lock().unwrap(),
}
}
fn lock_m_m(&self) -> MutexGuardWrapperWrapper<'_> {
MutexGuardWrapperWrapper {
mg: MutexGuardWrapper {
mg: self.m.lock().unwrap(),
},
}
}
fn foo(&self) -> bool {
true
}
fn bar(&self) {}
}
fn should_trigger_lint_with_wrapped_mutex() {
let s = StateWithMutex { m: Mutex::new(1) };
// Should trigger lint because a temporary contains a type with a significant drop and its
// lifetime is not obvious. Additionally, it is not obvious from looking at the scrutinee that
// the temporary contains such a type, making it potentially even more surprising.
match s.lock_m().get_the_value() {
1 => {
println!("Got 1. Is it still 1?");
println!("{}", s.lock_m().get_the_value());
},
2 => {
println!("Got 2. Is it still 2?");
println!("{}", s.lock_m().get_the_value());
},
_ => {},
}
println!("All done!");
}
fn should_trigger_lint_with_double_wrapped_mutex() {
let s = StateWithMutex { m: Mutex::new(1) };
// Should trigger lint because a temporary contains a type which further contains a type with a
// significant drop and its lifetime is not obvious. Additionally, it is not obvious from
// looking at the scrutinee that the temporary contains such a type, making it potentially even
// more surprising.
match s.lock_m_m().get_the_value() {
1 => {
println!("Got 1. Is it still 1?");
println!("{}", s.lock_m().get_the_value());
},
2 => {
println!("Got 2. Is it still 2?");
println!("{}", s.lock_m().get_the_value());
},
_ => {},
}
println!("All done!");
}
struct Counter {
i: AtomicU64,
}
#[clippy::has_significant_drop]
struct CounterWrapper<'a> {
counter: &'a Counter,
}
impl<'a> CounterWrapper<'a> {
fn new(counter: &Counter) -> CounterWrapper {
counter.i.fetch_add(1, Ordering::Relaxed);
CounterWrapper { counter }
}
}
impl<'a> Drop for CounterWrapper<'a> {
fn drop(&mut self) {
self.counter.i.fetch_sub(1, Ordering::Relaxed);
}
}
impl Counter {
fn temp_increment(&self) -> Vec<CounterWrapper> {
vec![CounterWrapper::new(self), CounterWrapper::new(self)]
}
}
fn should_trigger_lint_for_vec() {
let counter = Counter { i: AtomicU64::new(0) };
// Should trigger lint because the temporary in the scrutinee returns a collection of types
// which have significant drops. The types with significant drops are also non-obvious when
// reading the expression in the scrutinee.
match counter.temp_increment().len() {
2 => {
let current_count = counter.i.load(Ordering::Relaxed);
println!("Current count {}", current_count);
assert_eq!(current_count, 0);
},
1 => {},
3 => {},
_ => {},
};
}
struct StateWithField {
s: String,
}
// Should trigger lint only on the type in the tuple which is created using a temporary
// with a significant drop. Additionally, this test ensures that the format of the tuple
// is preserved correctly in the suggestion.
fn should_trigger_lint_for_tuple_in_scrutinee() {
let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() });
{
match (mutex1.lock().unwrap().s.len(), true) {
(3, _) => {
println!("started");
mutex1.lock().unwrap().s.len();
println!("done");
},
(_, _) => {},
};
match (true, mutex1.lock().unwrap().s.len(), true) {
(_, 3, _) => {
println!("started");
mutex1.lock().unwrap().s.len();
println!("done");
},
(_, _, _) => {},
};
let mutex2 = Mutex::new(StateWithField { s: "two".to_owned() });
match (mutex1.lock().unwrap().s.len(), true, mutex2.lock().unwrap().s.len()) {
(3, _, 3) => {
println!("started");
mutex1.lock().unwrap().s.len();
mutex2.lock().unwrap().s.len();
println!("done");
},
(_, _, _) => {},
};
let mutex3 = Mutex::new(StateWithField { s: "three".to_owned() });
match mutex3.lock().unwrap().s.as_str() {
"three" => {
println!("started");
mutex1.lock().unwrap().s.len();
mutex2.lock().unwrap().s.len();
println!("done");
},
_ => {},
};
match (true, mutex3.lock().unwrap().s.as_str()) {
(_, "three") => {
println!("started");
mutex1.lock().unwrap().s.len();
mutex2.lock().unwrap().s.len();
println!("done");
},
(_, _) => {},
};
}
}
// Should trigger lint when either side of a binary operation creates a temporary with a
// significant drop.
// To avoid potential unnecessary copies or creating references that would trigger the significant
// drop problem, the lint recommends moving the entire binary operation.
fn should_trigger_lint_for_accessing_field_in_mutex_in_one_side_of_binary_op() {
let mutex = Mutex::new(StateWithField { s: "state".to_owned() });
match mutex.lock().unwrap().s.len() > 1 {
true => {
mutex.lock().unwrap().s.len();
},
false => {},
};
match 1 < mutex.lock().unwrap().s.len() {
true => {
mutex.lock().unwrap().s.len();
},
false => {},
};
}
// Should trigger lint when both sides of a binary operation creates a temporary with a
// significant drop.
// To avoid potential unnecessary copies or creating references that would trigger the significant
// drop problem, the lint recommends moving the entire binary operation.
fn should_trigger_lint_for_accessing_fields_in_mutex_in_both_sides_of_binary_op() {
let mutex1 = Mutex::new(StateWithField { s: "state".to_owned() });
let mutex2 = Mutex::new(StateWithField {
s: "statewithfield".to_owned(),
});
match mutex1.lock().unwrap().s.len() < mutex2.lock().unwrap().s.len() {
true => {
println!(
"{} < {}",
mutex1.lock().unwrap().s.len(),
mutex2.lock().unwrap().s.len()
);
},
false => {},
};
match mutex1.lock().unwrap().s.len() >= mutex2.lock().unwrap().s.len() {
true => {
println!(
"{} >= {}",
mutex1.lock().unwrap().s.len(),
mutex2.lock().unwrap().s.len()
);
},
false => {},
};
}
fn should_not_trigger_lint_for_closure_in_scrutinee() {
let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() });
let get_mutex_guard = || mutex1.lock().unwrap().s.len();
// Should not trigger lint because the temporary with a significant drop will be dropped
// at the end of the closure, so the MutexGuard will be unlocked and not have a potentially
// surprising lifetime.
match get_mutex_guard() > 1 {
true => {
mutex1.lock().unwrap().s.len();
},
false => {},
};
}
fn should_trigger_lint_for_return_from_closure_in_scrutinee() {
let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() });
let get_mutex_guard = || mutex1.lock().unwrap();
// Should trigger lint because the temporary with a significant drop is returned from the
// closure but not used directly in any match arms, so it has a potentially surprising lifetime.
match get_mutex_guard().s.len() > 1 {
true => {
mutex1.lock().unwrap().s.len();
},
false => {},
};
}
fn should_trigger_lint_for_return_from_match_in_scrutinee() {
let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() });
let mutex2 = Mutex::new(StateWithField { s: "two".to_owned() });
let i = 100;
// Should trigger lint because the nested match within the scrutinee returns a temporary with a
// significant drop is but not used directly in any match arms, so it has a potentially
// surprising lifetime.
match match i {
100 => mutex1.lock().unwrap(),
_ => mutex2.lock().unwrap(),
}
.s
.len()
> 1
{
true => {
mutex1.lock().unwrap().s.len();
},
false => {
println!("nothing to do here");
},
};
}
fn should_trigger_lint_for_return_from_if_in_scrutinee() {
let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() });
let mutex2 = Mutex::new(StateWithField { s: "two".to_owned() });
let i = 100;
// Should trigger lint because the nested if-expression within the scrutinee returns a temporary
// with a significant drop is but not used directly in any match arms, so it has a potentially
// surprising lifetime.
match if i > 1 {
mutex1.lock().unwrap()
} else {
mutex2.lock().unwrap()
}
.s
.len()
> 1
{
true => {
mutex1.lock().unwrap().s.len();
},
false => {},
};
}
fn should_not_trigger_lint_for_if_in_scrutinee() {
let mutex = Mutex::new(StateWithField { s: "state".to_owned() });
let i = 100;
// Should not trigger the lint because the temporary with a significant drop *is* dropped within
// the body of the if-expression nested within the match scrutinee, and therefore does not have
// a potentially surprising lifetime.
match if i > 1 {
mutex.lock().unwrap().s.len() > 1
} else {
false
} {
true => {
mutex.lock().unwrap().s.len();
},
false => {},
};
}
struct StateWithBoxedMutexGuard {
u: Mutex<u64>,
}
impl StateWithBoxedMutexGuard {
fn new() -> StateWithBoxedMutexGuard {
StateWithBoxedMutexGuard { u: Mutex::new(42) }
}
fn lock(&self) -> Box<MutexGuard<u64>> {
Box::new(self.u.lock().unwrap())
}
}
fn should_trigger_lint_for_boxed_mutex_guard() {
let s = StateWithBoxedMutexGuard::new();
// Should trigger lint because a temporary Box holding a type with a significant drop in a match
// scrutinee may have a potentially surprising lifetime.
match s.lock().deref().deref() {
0 | 1 => println!("Value was less than 2"),
_ => println!("Value is {}", s.lock().deref()),
};
}
struct StateStringWithBoxedMutexGuard {
s: Mutex<String>,
}
impl StateStringWithBoxedMutexGuard {
fn new() -> StateStringWithBoxedMutexGuard {
StateStringWithBoxedMutexGuard {
s: Mutex::new("A String".to_owned()),
}
}
fn lock(&self) -> Box<MutexGuard<String>> {
Box::new(self.s.lock().unwrap())
}
}
fn should_trigger_lint_for_boxed_mutex_guard_holding_string() {
let s = StateStringWithBoxedMutexGuard::new();
let matcher = String::from("A String");
// Should trigger lint because a temporary Box holding a type with a significant drop in a match
// scrutinee may have a potentially surprising lifetime.
match s.lock().deref().deref() {
matcher => println!("Value is {}", s.lock().deref()),
_ => println!("Value was not a match"),
};
}
struct StateWithIntField {
i: u64,
}
// Should trigger lint when either side of an assign expression contains a temporary with a
// significant drop, because the temporary's lifetime will be extended to the end of the match.
// To avoid potential unnecessary copies or creating references that would trigger the significant
// drop problem, the lint recommends moving the entire binary operation.
fn should_trigger_lint_in_assign_expr() {
let mutex = Mutex::new(StateWithIntField { i: 10 });
let mut i = 100;
match mutex.lock().unwrap().i = i {
_ => {
println!("{}", mutex.lock().unwrap().i);
},
};
match i = mutex.lock().unwrap().i {
_ => {
println!("{}", mutex.lock().unwrap().i);
},
};
match mutex.lock().unwrap().i += 1 {
_ => {
println!("{}", mutex.lock().unwrap().i);
},
};
match i += mutex.lock().unwrap().i {
_ => {
println!("{}", mutex.lock().unwrap().i);
},
};
}
#[derive(Debug)]
enum RecursiveEnum {
Foo(Option<Box<RecursiveEnum>>),
}
#[derive(Debug)]
enum GenericRecursiveEnum<T> {
Foo(T, Option<Box<GenericRecursiveEnum<T>>>),
}
fn should_not_cause_stack_overflow() {
// Test that when a type recursively contains itself, a stack overflow does not occur when
// checking sub-types for significant drops.
let f = RecursiveEnum::Foo(Some(Box::new(RecursiveEnum::Foo(None))));
match f {
RecursiveEnum::Foo(Some(f)) => {
println!("{:?}", f)
},
RecursiveEnum::Foo(f) => {
println!("{:?}", f)
},
}
let f = GenericRecursiveEnum::Foo(1u64, Some(Box::new(GenericRecursiveEnum::Foo(2u64, None))));
match f {
GenericRecursiveEnum::Foo(i, Some(f)) => {
println!("{} {:?}", i, f)
},
GenericRecursiveEnum::Foo(i, f) => {
println!("{} {:?}", i, f)
},
}
}
fn should_not_produce_lint_for_try_desugar() -> Result<u64, ParseIntError> {
// TryDesugar (i.e. using `?` for a Result type) will turn into a match but is out of scope
// for this lint
let rwlock = RwLock::new("1".to_string());
let result = rwlock.read().unwrap().parse::<u64>()?;
println!("{}", result);
rwlock.write().unwrap().push('2');
Ok(result)
}
struct ResultReturner {
s: String,
}
impl ResultReturner {
fn to_number(&self) -> Result<i64, ParseIntError> {
self.s.parse::<i64>()
}
}
fn should_trigger_lint_for_non_ref_move_and_clone_suggestion() {
let rwlock = RwLock::<ResultReturner>::new(ResultReturner { s: "1".to_string() });
match rwlock.read().unwrap().to_number() {
Ok(n) => println!("Converted to number: {}", n),
Err(e) => println!("Could not convert {} to number", e),
};
}
fn should_trigger_lint_for_read_write_lock_for_loop() {
// For-in loops desugar to match expressions and are prone to the type of deadlock this lint is
// designed to look for.
let rwlock = RwLock::<Vec<String>>::new(vec!["1".to_string()]);
for s in rwlock.read().unwrap().iter() {
println!("{}", s);
}
}
fn do_bar(mutex: &Mutex<State>) {
mutex.lock().unwrap().bar();
}
fn should_trigger_lint_without_significant_drop_in_arm() {
let mutex = Mutex::new(State {});
// Should trigger lint because the lifetime of the temporary MutexGuard is surprising because it
// is preserved until the end of the match, but there is no clear indication that this is the
// case.
match mutex.lock().unwrap().foo() {
true => do_bar(&mutex),
false => {},
};
}
fn should_not_trigger_on_significant_iterator_drop() {
let lines = std::io::stdin().lines();
for line in lines {
println!("foo: {}", line.unwrap());
}
}
fn main() {}