Auto merge of #4736 - flip1995:icu_mul_add, r=matthiaskrgr

Move manual_mul_add into nursery

Addresses #4735

changelog: Move [`manual_mul_add`] into nursery

clippy_lints/src/lib.rs

@@ -1183,7 +1183,6 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&misc_early::UNNEEDED_FIELD_PATTERN),
         LintId::of(&misc_early::UNNEEDED_WILDCARD_PATTERN),
         LintId::of(&misc_early::ZERO_PREFIXED_LITERAL),
-        LintId::of(&mul_add::MANUAL_MUL_ADD),
         LintId::of(&mut_reference::UNNECESSARY_MUT_PASSED),
         LintId::of(&mutable_debug_assertion::DEBUG_ASSERT_WITH_MUT_CALL),
         LintId::of(&mutex_atomic::MUTEX_ATOMIC),
@@ -1527,7 +1526,6 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&methods::OR_FUN_CALL),
         LintId::of(&methods::SINGLE_CHAR_PATTERN),
         LintId::of(&misc::CMP_OWNED),
-        LintId::of(&mul_add::MANUAL_MUL_ADD),
         LintId::of(&mutex_atomic::MUTEX_ATOMIC),
         LintId::of(&redundant_clone::REDUNDANT_CLONE),
         LintId::of(&slow_vector_initialization::SLOW_VECTOR_INITIALIZATION),
@@ -1546,6 +1544,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&attrs::EMPTY_LINE_AFTER_OUTER_ATTR),
         LintId::of(&fallible_impl_from::FALLIBLE_IMPL_FROM),
         LintId::of(&missing_const_for_fn::MISSING_CONST_FOR_FN),
+        LintId::of(&mul_add::MANUAL_MUL_ADD),
         LintId::of(&mutex_atomic::MUTEX_INTEGER),
         LintId::of(&needless_borrow::NEEDLESS_BORROW),
         LintId::of(&path_buf_push_overwrite::PATH_BUF_PUSH_OVERWRITE),

clippy_lints/src/mul_add.rs

@@ -15,7 +15,9 @@
     /// `c`. Depending on the target architecture, `mul_add()` may be more
     /// performant.
     ///
-    /// **Known problems:** None.
+    /// **Known problems:** This lint can emit semantic incorrect suggestions.
+    /// For example, for `a * b * c + d` the suggestion `a * b.mul_add(c, d)`
+    /// is emitted, which is equivalent to `a * (b * c + d)`. (#4735)
     ///
     /// **Example:**
     ///
@@ -35,7 +37,7 @@
     /// let foo = a.mul_add(b, c);
     /// ```
     pub MANUAL_MUL_ADD,
-    perf,
+    nursery,
     "Using `a.mul_add(b, c)` for floating points has higher numerical precision than `a * b + c`"
 }
 

src/lintlist/mod.rs

@@ -961,7 +961,7 @@
     },
     Lint {
         name: "manual_mul_add",
-        group: "perf",
+        group: "nursery",
         desc: "Using `a.mul_add(b, c)` for floating points has higher numerical precision than `a * b + c`",
         deprecation: None,
         module: "mul_add",