[early_drop_lock] Add initial skeleton

Author: c410-f3r

CHANGELOG.md

@@ -4158,6 +4158,7 @@ Released 2018-09-13
 [`duplicate_mod`]: https://rust-lang.github.io/rust-clippy/master/index.html#duplicate_mod
 [`duplicate_underscore_argument`]: https://rust-lang.github.io/rust-clippy/master/index.html#duplicate_underscore_argument
 [`duration_subsec`]: https://rust-lang.github.io/rust-clippy/master/index.html#duration_subsec
+[`early_drop_lock`]: https://rust-lang.github.io/rust-clippy/master/index.html#early_drop_lock
 [`else_if_without_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#else_if_without_else
 [`empty_drop`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_drop
 [`empty_enum`]: https://rust-lang.github.io/rust-clippy/master/index.html#empty_enum

clippy_lints/src/declared_lints.rs

@@ -137,6 +137,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::drop_forget_ref::FORGET_REF_INFO,
     crate::drop_forget_ref::UNDROPPED_MANUALLY_DROPS_INFO,
     crate::duplicate_mod::DUPLICATE_MOD_INFO,
+    crate::early_drop_lock::EARLY_DROP_LOCK_INFO,
     crate::else_if_without_else::ELSE_IF_WITHOUT_ELSE_INFO,
     crate::empty_drop::EMPTY_DROP_INFO,
     crate::empty_enum::EMPTY_ENUM_INFO,

clippy_lints/src/early_drop_lock.rs

@@ -0,0 +1,43 @@
+use rustc_lint::LateLintPass;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// Searches for lock primitives that could be early dropped but are in fact dropped at the end
+    /// of their scopes.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// A lock unnecessarily held can imply unnecessary resource contention.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// fn example() {
+    ///   let locked = some_sync_resource.lock();
+    ///   let owned_rslt = locked.do_stuff_with_resource();
+    ///   // Only `owned_rslt` is needed but `locked` is still held
+    ///   do_heavy_computation_that_takes_time(owned_rslt);
+    /// }
+    /// ```
+    ///
+    /// Use instead:
+    ///
+    /// ```rust
+    /// fn example() {
+    ///     let owned_rslt = some_sync_resource.lock().do_stuff_with_resource();
+    ///     do_heavy_computation_that_takes_time(owned_rslt);
+    /// }
+    /// ```
+    #[clippy::version = "1.67.0"]
+    pub EARLY_DROP_LOCK,
+    nursery,
+    "Searches for lock primitives that could be early dropped in order to prevent unnecessary resource contention."
+}
+
+impl_lint_pass!(EarlyDropLock => [EARLY_DROP_LOCK]);
+
+pub struct EarlyDropLock;
+
+impl<'tcx> LateLintPass<'tcx> for EarlyDropLock {}

clippy_lints/src/lib.rs

@@ -108,6 +108,7 @@ mod doc;
 mod double_parens;
 mod drop_forget_ref;
 mod duplicate_mod;
+mod early_drop_lock;
 mod else_if_without_else;
 mod empty_drop;
 mod empty_enum;
@@ -557,6 +558,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|_| Box::new(eta_reduction::EtaReduction));
     store.register_late_pass(|_| Box::new(mut_mut::MutMut));
     store.register_late_pass(|_| Box::new(mut_reference::UnnecessaryMutPassed));
+    store.register_late_pass(|_| Box::new(early_drop_lock::EarlyDropLock));
     store.register_late_pass(|_| Box::new(len_zero::LenZero));
     store.register_late_pass(|_| Box::new(attrs::Attributes));
     store.register_late_pass(|_| Box::new(blocks_in_if_conditions::BlocksInIfConditions));