Auto merge of #109732 - Urgau:uplift_drop_forget_ref_lints, r=davidtwco

Uplift `clippy::{drop,forget}_{ref,copy}` lints

This PR aims at uplifting the `clippy::drop_ref`, `clippy::drop_copy`, `clippy::forget_ref` and `clippy::forget_copy` lints.

Those lints are/were declared in the correctness category of clippy because they lint on useless and most probably is not what the developer wanted.

## `drop_ref` and `forget_ref`

The `drop_ref` and `forget_ref` lint checks for calls to `std::mem::drop` or `std::mem::forget` with a reference instead of an owned value.

### Example

```rust
let mut lock_guard = mutex.lock();
std::mem::drop(&lock_guard) // Should have been drop(lock_guard), mutex
// still locked
operation_that_requires_mutex_to_be_unlocked();
```

### Explanation

Calling `drop` or `forget` on a reference will only drop the reference itself, which is a no-op. It will not call the `drop` or `forget` method on the underlying referenced value, which is likely what was intended.

## `drop_copy` and `forget_copy`

The `drop_copy` and `forget_copy` lint checks for calls to `std::mem::forget` or `std::mem::drop` with a value that derives the Copy trait.

### Example

```rust
let x: i32 = 42; // i32 implements Copy
std::mem::forget(x) // A copy of x is passed to the function, leaving the
                    // original unaffected
```

### Explanation

Calling `std::mem::forget` [does nothing for types that implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html) since the value will be copied and moved into the function on invocation.

-----

Followed the instructions for uplift a clippy describe here: rust-lang/rust#99696 (review)

cc `@m-ou-se` (as T-libs-api leader because the uplifting was discussed in a recent meeting)

Author: bors

clippy_lints/src/declared_lints.rs

@@ -132,12 +132,8 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::doc::NEEDLESS_DOCTEST_MAIN_INFO,
     crate::doc::UNNECESSARY_SAFETY_DOC_INFO,
     crate::double_parens::DOUBLE_PARENS_INFO,
-    crate::drop_forget_ref::DROP_COPY_INFO,
     crate::drop_forget_ref::DROP_NON_DROP_INFO,
-    crate::drop_forget_ref::DROP_REF_INFO,
-    crate::drop_forget_ref::FORGET_COPY_INFO,
     crate::drop_forget_ref::FORGET_NON_DROP_INFO,
-    crate::drop_forget_ref::FORGET_REF_INFO,
     crate::drop_forget_ref::UNDROPPED_MANUALLY_DROPS_INFO,
     crate::duplicate_mod::DUPLICATE_MOD_INFO,
     crate::else_if_without_else::ELSE_IF_WITHOUT_ELSE_INFO,

clippy_lints/src/drop_forget_ref.rs

@@ -7,102 +7,6 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for calls to `std::mem::drop` with a reference
-    /// instead of an owned value.
-    ///
-    /// ### Why is this bad?
-    /// Calling `drop` on a reference will only drop the
-    /// reference itself, which is a no-op. It will not call the `drop` method (from
-    /// the `Drop` trait implementation) on the underlying referenced value, which
-    /// is likely what was intended.
-    ///
-    /// ### Example
-    /// ```ignore
-    /// let mut lock_guard = mutex.lock();
-    /// std::mem::drop(&lock_guard) // Should have been drop(lock_guard), mutex
-    /// // still locked
-    /// operation_that_requires_mutex_to_be_unlocked();
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub DROP_REF,
-    correctness,
-    "calls to `std::mem::drop` with a reference instead of an owned value"
-}
-
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for calls to `std::mem::forget` with a reference
-    /// instead of an owned value.
-    ///
-    /// ### Why is this bad?
-    /// Calling `forget` on a reference will only forget the
-    /// reference itself, which is a no-op. It will not forget the underlying
-    /// referenced
-    /// value, which is likely what was intended.
-    ///
-    /// ### Example
-    /// ```rust
-    /// let x = Box::new(1);
-    /// std::mem::forget(&x) // Should have been forget(x), x will still be dropped
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub FORGET_REF,
-    correctness,
-    "calls to `std::mem::forget` with a reference instead of an owned value"
-}
-
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for calls to `std::mem::drop` with a value
-    /// that derives the Copy trait
-    ///
-    /// ### Why is this bad?
-    /// Calling `std::mem::drop` [does nothing for types that
-    /// implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html), since the
-    /// value will be copied and moved into the function on invocation.
-    ///
-    /// ### Example
-    /// ```rust
-    /// let x: i32 = 42; // i32 implements Copy
-    /// std::mem::drop(x) // A copy of x is passed to the function, leaving the
-    ///                   // original unaffected
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub DROP_COPY,
-    correctness,
-    "calls to `std::mem::drop` with a value that implements Copy"
-}
-
-declare_clippy_lint! {
-    /// ### What it does
-    /// Checks for calls to `std::mem::forget` with a value that
-    /// derives the Copy trait
-    ///
-    /// ### Why is this bad?
-    /// Calling `std::mem::forget` [does nothing for types that
-    /// implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html) since the
-    /// value will be copied and moved into the function on invocation.
-    ///
-    /// An alternative, but also valid, explanation is that Copy types do not
-    /// implement
-    /// the Drop trait, which means they have no destructors. Without a destructor,
-    /// there
-    /// is nothing for `std::mem::forget` to ignore.
-    ///
-    /// ### Example
-    /// ```rust
-    /// let x: i32 = 42; // i32 implements Copy
-    /// std::mem::forget(x) // A copy of x is passed to the function, leaving the
-    ///                     // original unaffected
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub FORGET_COPY,
-    correctness,
-    "calls to `std::mem::forget` with a value that implements Copy"
-}
-
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for calls to `std::mem::drop` with a value that does not implement `Drop`.
@@ -172,24 +76,12 @@ declare_clippy_lint! {
     "use of safe `std::mem::drop` function to drop a std::mem::ManuallyDrop, which will not drop the inner value"
 }
 
-const DROP_REF_SUMMARY: &str = "calls to `std::mem::drop` with a reference instead of an owned value. \
-                                Dropping a reference does nothing";
-const FORGET_REF_SUMMARY: &str = "calls to `std::mem::forget` with a reference instead of an owned value. \
-                                  Forgetting a reference does nothing";
-const DROP_COPY_SUMMARY: &str = "calls to `std::mem::drop` with a value that implements `Copy`. \
-                                 Dropping a copy leaves the original intact";
-const FORGET_COPY_SUMMARY: &str = "calls to `std::mem::forget` with a value that implements `Copy`. \
-                                   Forgetting a copy leaves the original intact";
 const DROP_NON_DROP_SUMMARY: &str = "call to `std::mem::drop` with a value that does not implement `Drop`. \
                                  Dropping such a type only extends its contained lifetimes";
 const FORGET_NON_DROP_SUMMARY: &str = "call to `std::mem::forget` with a value that does not implement `Drop`. \
                                    Forgetting such a type is the same as dropping it";
 
 declare_lint_pass!(DropForgetRef => [
-    DROP_REF,
-    FORGET_REF,
-    DROP_COPY,
-    FORGET_COPY,
     DROP_NON_DROP,
     FORGET_NON_DROP,
     UNDROPPED_MANUALLY_DROPS
@@ -206,10 +98,11 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
             let is_copy = is_copy(cx, arg_ty);
             let drop_is_single_call_in_arm = is_single_call_in_arm(cx, arg, expr);
             let (lint, msg) = match fn_name {
-                sym::mem_drop if arg_ty.is_ref() && !drop_is_single_call_in_arm => (DROP_REF, DROP_REF_SUMMARY),
-                sym::mem_forget if arg_ty.is_ref() => (FORGET_REF, FORGET_REF_SUMMARY),
-                sym::mem_drop if is_copy && !drop_is_single_call_in_arm => (DROP_COPY, DROP_COPY_SUMMARY),
-                sym::mem_forget if is_copy => (FORGET_COPY, FORGET_COPY_SUMMARY),
+                // early return for uplifted lints: drop_ref, drop_copy, forget_ref, forget_copy
+                sym::mem_drop if arg_ty.is_ref() && !drop_is_single_call_in_arm => return,
+                sym::mem_forget if arg_ty.is_ref() => return,
+                sym::mem_drop if is_copy && !drop_is_single_call_in_arm => return,
+                sym::mem_forget if is_copy => return,
                 sym::mem_drop if is_type_lang_item(cx, arg_ty, LangItem::ManuallyDrop) => {
                     span_lint_and_help(
                         cx,

clippy_lints/src/renamed_lints.rs

@@ -32,9 +32,13 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::zero_width_space", "clippy::invisible_characters"),
     ("clippy::clone_double_ref", "suspicious_double_ref_op"),
     ("clippy::drop_bounds", "drop_bounds"),
+    ("clippy::drop_copy", "drop_copy"),
+    ("clippy::drop_ref", "drop_ref"),
     ("clippy::for_loop_over_option", "for_loops_over_fallibles"),
     ("clippy::for_loop_over_result", "for_loops_over_fallibles"),
     ("clippy::for_loops_over_fallibles", "for_loops_over_fallibles"),
+    ("clippy::forget_copy", "forget_copy"),
+    ("clippy::forget_ref", "forget_ref"),
     ("clippy::into_iter_on_array", "array_into_iter"),
     ("clippy::invalid_atomic_ordering", "invalid_atomic_ordering"),
     ("clippy::invalid_ref", "invalid_value"),