Create clippy lint against unexpectedly late drop for temporaries in match scrutinee expressions

library/std/src/sync/mutex.rs

@@ -192,6 +192,7 @@ unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
                       points can cause deadlocks, delays, \
                       and cause Futures to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[clippy::has_significant_drop]
 pub struct MutexGuard<'a, T: ?Sized + 'a> {
     lock: &'a Mutex<T>,
     poison: poison::Guard,

library/std/src/sync/rwlock.rs

@@ -99,6 +99,7 @@ unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
                       points can cause deadlocks, delays, \
                       and cause Futures to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[clippy::has_significant_drop]
 pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
     lock: &'a RwLock<T>,
 }
@@ -122,6 +123,7 @@ unsafe impl<T: ?Sized + Sync> Sync for RwLockReadGuard<'_, T> {}
                       points can cause deadlocks, delays, \
                       and cause Future's to not implement `Send`"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[clippy::has_significant_drop]
 pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
     lock: &'a RwLock<T>,
     poison: poison::Guard,

src/tools/clippy/CHANGELOG.md

@@ -3696,6 +3696,7 @@ Released 2018-09-13
 [`skip_while_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#skip_while_next
 [`slow_vector_initialization`]: https://rust-lang.github.io/rust-clippy/master/index.html#slow_vector_initialization
 [`stable_sort_primitive`]: https://rust-lang.github.io/rust-clippy/master/index.html#stable_sort_primitive
+[`significant_drop_in_scrutinee`]: https://rust-lang.github.io/rust-clippy/master/index.html#significant_drop_in_scrutinee
 [`str_to_string`]: https://rust-lang.github.io/rust-clippy/master/index.html#str_to_string
 [`string_add`]: https://rust-lang.github.io/rust-clippy/master/index.html#string_add
 [`string_add_assign`]: https://rust-lang.github.io/rust-clippy/master/index.html#string_add_assign

src/tools/clippy/clippy_lints/src/lib.register_lints.rs

@@ -475,6 +475,7 @@ store.register_lints(&[
     size_of_in_element_count::SIZE_OF_IN_ELEMENT_COUNT,
     slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,
     stable_sort_primitive::STABLE_SORT_PRIMITIVE,
+    significant_drop_in_scrutinee::SIGNIFICANT_DROP_IN_SCRUTINEE,
     strings::STRING_ADD,
     strings::STRING_ADD_ASSIGN,
     strings::STRING_FROM_UTF8_AS_BYTES,

src/tools/clippy/clippy_lints/src/lib.register_nursery.rs

@@ -25,6 +25,7 @@ store.register_group(true, "clippy::nursery", Some("clippy_nursery"), vec![
     LintId::of(path_buf_push_overwrite::PATH_BUF_PUSH_OVERWRITE),
     LintId::of(redundant_pub_crate::REDUNDANT_PUB_CRATE),
     LintId::of(regex::TRIVIAL_REGEX),
+    LintId::of(significant_drop_in_scrutinee::SIGNIFICANT_DROP_IN_SCRUTINEE),
     LintId::of(strings::STRING_LIT_AS_BYTES),
     LintId::of(suspicious_operation_groupings::SUSPICIOUS_OPERATION_GROUPINGS),
     LintId::of(trailing_empty_array::TRAILING_EMPTY_ARRAY),

src/tools/clippy/clippy_lints/src/lib.rs

@@ -364,6 +364,7 @@ mod self_named_constructors;
 mod semicolon_if_nothing_returned;
 mod serde_api;
 mod shadow;
+mod significant_drop_in_scrutinee;
 mod single_char_lifetime_names;
 mod single_component_path_imports;
 mod size_of_in_element_count;
@@ -874,6 +875,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(move || Box::new(manual_bits::ManualBits::new(msrv)));
     store.register_late_pass(|| Box::new(default_union_representation::DefaultUnionRepresentation));
     store.register_late_pass(|| Box::new(only_used_in_recursion::OnlyUsedInRecursion));
+    store.register_late_pass(|| Box::new(significant_drop_in_scrutinee::SignificantDropInScrutinee));
     store.register_late_pass(|| Box::new(dbg_macro::DbgMacro));
     let cargo_ignore_publish = conf.cargo_ignore_publish;
     store.register_late_pass(move || {