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Auto merge of #5101 - Areredify:let_underscore_lock, r=flip1995

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add `let_underscore_lock` lint

closes #1574
changelog: add `let_underscore_lock` lint

I am not entirely sure about my docs/messages wording here, improvements are welcome
This commit is contained in:
bors 2020-01-30 20:24:24 +00:00
commit 668bc485da
10 changed files with 139 additions and 18 deletions
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1
CHANGELOG.md
View file

@ -1153,6 +1153,7 @@ Released 2018-09-13
[`len_without_is_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#len_without_is_empty
[`len_zero`]: https://rust-lang.github.io/rust-clippy/master/index.html#len_zero
[`let_and_return`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_and_return
[`let_underscore_lock`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_lock
[`let_underscore_must_use`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_must_use
[`let_unit_value`]: https://rust-lang.github.io/rust-clippy/master/index.html#let_unit_value
[`linkedlist`]: https://rust-lang.github.io/rust-clippy/master/index.html#linkedlist

2
README.md
View file

@ -6,7 +6,7 @@
A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
[There are 350 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
[There are 351 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:

51
clippy_lints/src/let_underscore.rs
View file

@ -4,7 +4,7 @@ use rustc_hir::*;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use crate::utils::{is_must_use_func_call, is_must_use_ty, span_lint_and_help};
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>`
@ -30,7 +30,40 @@ declare_clippy_lint! {
"non-binding let on a `#[must_use]` expression"
}
declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE]);
declare_clippy_lint! {
/// **What it does:** Checks for `let _ = sync_lock`
///
/// **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.
/// 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:
/// ```rust,ignore
/// let _ = mutex.lock();
/// ```
///
/// Good:
/// ```rust,ignore
/// let _lock = mutex.lock();
/// ```
pub LET_UNDERSCORE_LOCK,
correctness,
"non-binding let on a synchronization lock"
}
declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_MUST_USE, LET_UNDERSCORE_LOCK]);
const SYNC_GUARD_PATHS: [&[&str]; 3] = [
&paths::MUTEX_GUARD,
&paths::RWLOCK_READ_GUARD,
&paths::RWLOCK_WRITE_GUARD,
];
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore {
fn check_stmt(&mut self, cx: &LateContext<'_, '_>, stmt: &Stmt<'_>) {
@ -43,8 +76,18 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnderscore {
if let PatKind::Wild = local.pat.kind;
if let Some(ref init) = local.init;
then {
if is_must_use_ty(cx, cx.tables.expr_ty(init)) {
span_lint_and_help(
let check_ty = |ty| SYNC_GUARD_PATHS.iter().any(|path| match_type(cx, ty, path));
if cx.tables.expr_ty(init).walk().any(check_ty) {
span_lint_and_help(
cx,
LET_UNDERSCORE_LOCK,
stmt.span,
"non-binding let on a synchronization lock",
"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)) {
span_lint_and_help(
cx,
LET_UNDERSCORE_MUST_USE,
stmt.span,

3
clippy_lints/src/lib.rs
View file

@ -566,6 +566,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
&len_zero::LEN_WITHOUT_IS_EMPTY,
&len_zero::LEN_ZERO,
&let_if_seq::USELESS_LET_IF_SEQ,
&let_underscore::LET_UNDERSCORE_LOCK,
&let_underscore::LET_UNDERSCORE_MUST_USE,
&lifetimes::EXTRA_UNUSED_LIFETIMES,
&lifetimes::NEEDLESS_LIFETIMES,
@ -1171,6 +1172,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY),
LintId::of(&len_zero::LEN_ZERO),
LintId::of(&let_if_seq::USELESS_LET_IF_SEQ),
LintId::of(&let_underscore::LET_UNDERSCORE_LOCK),
LintId::of(&lifetimes::EXTRA_UNUSED_LIFETIMES),
LintId::of(&lifetimes::NEEDLESS_LIFETIMES),
LintId::of(&literal_representation::INCONSISTENT_DIGIT_GROUPING),
@ -1556,6 +1558,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&infinite_iter::INFINITE_ITER),
LintId::of(&inherent_to_string::INHERENT_TO_STRING_SHADOW_DISPLAY),
LintId::of(&inline_fn_without_body::INLINE_FN_WITHOUT_BODY),
LintId::of(&let_underscore::LET_UNDERSCORE_LOCK),
LintId::of(&literal_representation::MISTYPED_LITERAL_SUFFIXES),
LintId::of(&loops::FOR_LOOP_OVER_OPTION),
LintId::of(&loops::FOR_LOOP_OVER_RESULT),

3
clippy_lints/src/utils/paths.rs
View file

@ -58,6 +58,7 @@ pub const MEM_REPLACE: [&str; 3] = ["core", "mem", "replace"];
pub const MEM_UNINITIALIZED: [&str; 3] = ["core", "mem", "uninitialized"];
pub const MEM_ZEROED: [&str; 3] = ["core", "mem", "zeroed"];
pub const MUTEX: [&str; 4] = ["std", "sync", "mutex", "Mutex"];
pub const MUTEX_GUARD: [&str; 4] = ["std", "sync", "mutex", "MutexGuard"];
pub const OPEN_OPTIONS: [&str; 3] = ["std", "fs", "OpenOptions"];
pub const OPS_MODULE: [&str; 2] = ["core", "ops"];
pub const OPTION: [&str; 3] = ["core", "option", "Option"];
@ -100,6 +101,8 @@ pub const REPEAT: [&str; 3] = ["core", "iter", "repeat"];
pub const RESULT: [&str; 3] = ["core", "result", "Result"];
pub const RESULT_ERR: [&str; 4] = ["core", "result", "Result", "Err"];
pub const RESULT_OK: [&str; 4] = ["core", "result", "Result", "Ok"];
pub const RWLOCK_READ_GUARD: [&str; 4] = ["std", "sync", "rwlock", "RwLockReadGuard"];
pub const RWLOCK_WRITE_GUARD: [&str; 4] = ["std", "sync", "rwlock", "RwLockWriteGuard"];
pub const SERDE_DE_VISITOR: [&str; 3] = ["serde", "de", "Visitor"];
pub const SLICE_INTO_VEC: [&str; 4] = ["alloc", "slice", "<impl [T]>", "into_vec"];
pub const SLICE_ITER: [&str; 3] = ["core", "slice", "Iter"];

9
src/lintlist/mod.rs
View file

@ -6,7 +6,7 @@ pub use lint::Lint;
pub use lint::LINT_LEVELS;
// begin lint list, do not remove this comment, it’s used in `update_lints`
pub const ALL_LINTS: [Lint; 350] = [
pub const ALL_LINTS: [Lint; 351] = [
Lint {
name: "absurd_extreme_comparisons",
group: "correctness",
@ -959,6 +959,13 @@ pub const ALL_LINTS: [Lint; 350] = [
deprecation: None,
module: "returns",
},
Lint {
name: "let_underscore_lock",
group: "correctness",
desc: "non-binding let on a synchronization lock",
deprecation: None,
module: "let_underscore",
},
Lint {
name: "let_underscore_must_use",
group: "restriction",

13
tests/ui/let_underscore_lock.rs Normal file
View file

@ -0,0 +1,13 @@
#![warn(clippy::let_underscore_lock)]
fn main() {
let m = std::sync::Mutex::new(());
let rw = std::sync::RwLock::new(());
let _ = m.lock();
let _ = rw.read();
let _ = rw.write();
let _ = m.try_lock();
let _ = rw.try_read();
let _ = rw.try_write();
}

51
tests/ui/let_underscore_lock.stderr Normal file
View file

@ -0,0 +1,51 @@
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:7:5
|
LL | let _ = m.lock();
| ^^^^^^^^^^^^^^^^^
|
= note: `-D clippy::let-underscore-lock` implied by `-D warnings`
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:8:5
|
LL | let _ = rw.read();
| ^^^^^^^^^^^^^^^^^^
|
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:9:5
|
LL | let _ = rw.write();
| ^^^^^^^^^^^^^^^^^^^
|
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:10:5
|
LL | let _ = m.try_lock();
| ^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:11:5
|
LL | let _ = rw.try_read();
| ^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: non-binding let on a synchronization lock
--> $DIR/let_underscore_lock.rs:12:5
|
LL | let _ = rw.try_write();
| ^^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider using an underscore-prefixed named binding or dropping explicitly with `std::mem::drop`
error: aborting due to 6 previous errors

0
tests/ui/let_underscore.rs → tests/ui/let_underscore_must_use.rs
View file

24
tests/ui/let_underscore.stderr → tests/ui/let_underscore_must_use.stderr
View file

@ -1,5 +1,5 @@
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:66:5
--> $DIR/let_underscore_must_use.rs:66:5
|
LL | let _ = f();
| ^^^^^^^^^^^^
@ -8,7 +8,7 @@ LL | let _ = f();
= help: consider explicitly using function result
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:67:5
--> $DIR/let_underscore_must_use.rs:67:5
|
LL | let _ = g();
| ^^^^^^^^^^^^
@ -16,7 +16,7 @@ LL | let _ = g();
= help: consider explicitly using expression value
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:69:5
--> $DIR/let_underscore_must_use.rs:69:5
|
LL | let _ = l(0_u32);
| ^^^^^^^^^^^^^^^^^
@ -24,7 +24,7 @@ LL | let _ = l(0_u32);
= help: consider explicitly using function result
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:73:5
--> $DIR/let_underscore_must_use.rs:73:5
|
LL | let _ = s.f();
| ^^^^^^^^^^^^^^
@ -32,7 +32,7 @@ LL | let _ = s.f();
= help: consider explicitly using function result
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:74:5
--> $DIR/let_underscore_must_use.rs:74:5
|
LL | let _ = s.g();
| ^^^^^^^^^^^^^^
@ -40,7 +40,7 @@ LL | let _ = s.g();
= help: consider explicitly using expression value
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:77:5
--> $DIR/let_underscore_must_use.rs:77:5
|
LL | let _ = S::h();
| ^^^^^^^^^^^^^^^
@ -48,7 +48,7 @@ LL | let _ = S::h();
= help: consider explicitly using function result
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:78:5
--> $DIR/let_underscore_must_use.rs:78:5
|
LL | let _ = S::p();
| ^^^^^^^^^^^^^^^
@ -56,7 +56,7 @@ LL | let _ = S::p();
= help: consider explicitly using expression value
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:80:5
--> $DIR/let_underscore_must_use.rs:80:5
|
LL | let _ = S::a();
| ^^^^^^^^^^^^^^^
@ -64,7 +64,7 @@ LL | let _ = S::a();
= help: consider explicitly using function result
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:82:5
--> $DIR/let_underscore_must_use.rs:82:5
|
LL | let _ = if true { Ok(()) } else { Err(()) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -72,7 +72,7 @@ LL | let _ = if true { Ok(()) } else { Err(()) };
= help: consider explicitly using expression value
error: non-binding let on a result of a `#[must_use]` function
--> $DIR/let_underscore.rs:86:5
--> $DIR/let_underscore_must_use.rs:86:5
|
LL | let _ = a.is_ok();
| ^^^^^^^^^^^^^^^^^^
@ -80,7 +80,7 @@ LL | let _ = a.is_ok();
= help: consider explicitly using function result
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:88:5
--> $DIR/let_underscore_must_use.rs:88:5
|
LL | let _ = a.map(|_| ());
| ^^^^^^^^^^^^^^^^^^^^^^
@ -88,7 +88,7 @@ LL | let _ = a.map(|_| ());
= help: consider explicitly using expression value
error: non-binding let on an expression with `#[must_use]` type
--> $DIR/let_underscore.rs:90:5
--> $DIR/let_underscore_must_use.rs:90:5
|
LL | let _ = a;
| ^^^^^^^^^^