Move unintentional_unit_return from nursery to correctness

Also rewrites the description to be clearer

clippy_lints/src/lib.rs

@@ -1426,6 +1426,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&types::UNNECESSARY_CAST),
         LintId::of(&types::VEC_BOX),
         LintId::of(&unicode::ZERO_WIDTH_SPACE),
+        LintId::of(&unintentional_unit_return::UNINTENTIONAL_UNIT_RETURN),
         LintId::of(&unnamed_address::FN_ADDRESS_COMPARISONS),
         LintId::of(&unnamed_address::VTABLE_ADDRESS_COMPARISONS),
         LintId::of(&unnecessary_sort_by::UNNECESSARY_SORT_BY),
@@ -1681,6 +1682,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&types::CAST_REF_TO_MUT),
         LintId::of(&types::UNIT_CMP),
         LintId::of(&unicode::ZERO_WIDTH_SPACE),
+        LintId::of(&unintentional_unit_return::UNINTENTIONAL_UNIT_RETURN),
         LintId::of(&unnamed_address::FN_ADDRESS_COMPARISONS),
         LintId::of(&unnamed_address::VTABLE_ADDRESS_COMPARISONS),
         LintId::of(&unused_io_amount::UNUSED_IO_AMOUNT),
@@ -1730,7 +1732,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&path_buf_push_overwrite::PATH_BUF_PUSH_OVERWRITE),
         LintId::of(&redundant_pub_crate::REDUNDANT_PUB_CRATE),
         LintId::of(&transmute::USELESS_TRANSMUTE),
-        LintId::of(&unintentional_unit_return::UNINTENTIONAL_UNIT_RETURN),
         LintId::of(&use_self::USE_SELF),
     ]);
 }

clippy_lints/src/unintentional_unit_return.rs

@@ -10,12 +10,13 @@ use rustc_span::{BytePos, Span};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for functions that expect closures of type
-    /// Fn(...) -> Ord where the implemented closure has a semi-colon
-    /// at the end of the last statement.
+    /// Fn(...) -> Ord where the implemented closure returns the unit type.
+    /// The lint also suggests to remove the semi-colon at the end of the statement if present.
     ///
-    /// **Why is this bad?** Likely the semi-colon is unintentional which
-    /// returns () instead of the result of last statement. Since () implements Ord
-    /// it doesn't cause a compilation error
+    /// **Why is this bad?** Likely, returning the unit type is unintentional, and
+    /// could simply be caused by an extra semi-colon. Since () implements Ord
+    /// it doesn't cause a compilation error.
+    /// This is the same reasoning behind the unit_cmp lint.
     ///
     /// **Known problems:** If returning unit is intentional, then there is no
     /// way of specifying this without triggering needless_return lint
@@ -27,8 +28,8 @@ declare_clippy_lint! {
     /// twins.sort_by_key(|x| { x.1; });
     /// ```
     pub UNINTENTIONAL_UNIT_RETURN,
-    nursery,
-    "fn arguments of type Fn(...) -> Once having last statements with a semi-colon, suggesting to remove the semi-colon if it is unintentional."
+    correctness,
+    "fn arguments of type Fn(...) -> Ord returning the unit type ()."
 }
 
 declare_lint_pass!(UnintentionalUnitReturn => [UNINTENTIONAL_UNIT_RETURN]);

src/lintlist/mod.rs

@@ -2252,8 +2252,8 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
     },
     Lint {
         name: "unintentional_unit_return",
-        group: "nursery",
-        desc: "fn arguments of type Fn(...) -> Once having last statements with a semi-colon, suggesting to remove the semi-colon if it is unintentional.",
+        group: "correctness",
+        desc: "fn arguments of type Fn(...) -> Ord returning the unit type ().",
         deprecation: None,
         module: "unintentional_unit_return",
     },