Uplift clippy::undropped_manually_drops lint

compiler/rustc_lint/messages.ftl

@@ -492,6 +492,10 @@ lint_tykind = usage of `ty::TyKind`
 lint_tykind_kind = usage of `ty::TyKind::<kind>`
     .suggestion = try using `ty::<kind>` directly
 
+lint_undropped_manually_drops = calls to `std::mem::drop` with `std::mem::ManuallyDrop` instead of the inner value does nothing
+    .label = argument has type `{$arg_ty}`
+    .suggestion = use `std::mem::ManuallyDrop::into_inner` to get the inner value
+
 lint_ungated_async_fn_track_caller = `#[track_caller]` on async functions is a no-op
      .label = this function will not propagate the caller location
 

compiler/rustc_lint/src/drop_forget_useless.rs

@@ -1,8 +1,12 @@
 use rustc_hir::{Arm, Expr, ExprKind, Node};
+use rustc_middle::ty;
 use rustc_span::sym;
 
 use crate::{
-    lints::{DropCopyDiag, DropRefDiag, ForgetCopyDiag, ForgetRefDiag},
+    lints::{
+        DropCopyDiag, DropRefDiag, ForgetCopyDiag, ForgetRefDiag, UndroppedManuallyDropsDiag,
+        UndroppedManuallyDropsSuggestion,
+    },
     LateContext, LateLintPass, LintContext,
 };
 
@@ -109,7 +113,29 @@ declare_lint! {
     "calls to `std::mem::forget` with a value that implements Copy"
 }
 
-declare_lint_pass!(DropForgetUseless => [DROPPING_REFERENCES, FORGETTING_REFERENCES, DROPPING_COPY_TYPES, FORGETTING_COPY_TYPES]);
+declare_lint! {
+    /// The `undropped_manually_drops` lint check for calls to `std::mem::drop` with
+    /// a value of `std::mem::ManuallyDrop` which doesn't drop.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// struct S;
+    /// drop(std::mem::ManuallyDrop::new(S));
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// `ManuallyDrop` does not drop it's inner value so calling `std::mem::drop` will
+    /// not drop the inner value of the `ManuallyDrop` either.
+    pub UNDROPPED_MANUALLY_DROPS,
+    Deny,
+    "calls to `std::mem::drop` with `std::mem::ManuallyDrop` instead of it's inner value"
+}
+
+declare_lint_pass!(DropForgetUseless => [DROPPING_REFERENCES, FORGETTING_REFERENCES, DROPPING_COPY_TYPES, FORGETTING_COPY_TYPES, UNDROPPED_MANUALLY_DROPS]);
 
 impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
@@ -134,6 +160,20 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
                 sym::mem_forget if is_copy => {
                     cx.emit_spanned_lint(FORGETTING_COPY_TYPES, expr.span, ForgetCopyDiag { arg_ty, label: arg.span });
                 }
+                sym::mem_drop if let ty::Adt(adt, _) = arg_ty.kind() && adt.is_manually_drop() => {
+                    cx.emit_spanned_lint(
+                        UNDROPPED_MANUALLY_DROPS,
+                        expr.span,
+                        UndroppedManuallyDropsDiag {
+                            arg_ty,
+                            label: arg.span,
+                            suggestion: UndroppedManuallyDropsSuggestion {
+                                start_span: arg.span.shrink_to_lo(),
+                                end_span: arg.span.shrink_to_hi()
+                            }
+                        }
+                    );
+                }
                 _ => return,
             };
         }

compiler/rustc_lint/src/lints.rs

@@ -699,6 +699,25 @@ pub struct ForgetCopyDiag<'a> {
     pub label: Span,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(lint_undropped_manually_drops)]
+pub struct UndroppedManuallyDropsDiag<'a> {
+    pub arg_ty: Ty<'a>,
+    #[label]
+    pub label: Span,
+    #[subdiagnostic]
+    pub suggestion: UndroppedManuallyDropsSuggestion,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(lint_suggestion, applicability = "machine-applicable")]
+pub struct UndroppedManuallyDropsSuggestion {
+    #[suggestion_part(code = "std::mem::ManuallyDrop::into_inner(")]
+    pub start_span: Span,
+    #[suggestion_part(code = ")")]
+    pub end_span: Span,
+}
+
 // invalid_from_utf8.rs
 #[derive(LintDiagnostic)]
 pub enum InvalidFromUtf8Diag {

library/core/tests/manually_drop.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(not(bootstrap), allow(undropped_manually_drops))]
+
 use core::mem::ManuallyDrop;
 
 #[test]

src/tools/clippy/clippy_lints/src/declared_lints.rs

@@ -136,7 +136,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::double_parens::DOUBLE_PARENS_INFO,
     crate::drop_forget_ref::DROP_NON_DROP_INFO,
     crate::drop_forget_ref::FORGET_NON_DROP_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,
     crate::empty_drop::EMPTY_DROP_INFO,

src/tools/clippy/clippy_lints/src/drop_forget_ref.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note};
+use clippy_utils::diagnostics::span_lint_and_note;
 use clippy_utils::get_parent_node;
 use clippy_utils::is_must_use_func_call;
 use clippy_utils::ty::{is_copy, is_must_use_ty, is_type_lang_item};
@@ -47,35 +47,6 @@ declare_clippy_lint! {
     "call to `std::mem::forget` with a value which does not implement `Drop`"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Prevents the safe `std::mem::drop` function from being called on `std::mem::ManuallyDrop`.
-    ///
-    /// ### Why is this bad?
-    /// The safe `drop` function does not drop the inner value of a `ManuallyDrop`.
-    ///
-    /// ### Known problems
-    /// Does not catch cases if the user binds `std::mem::drop`
-    /// to a different name and calls it that way.
-    ///
-    /// ### Example
-    /// ```rust
-    /// struct S;
-    /// drop(std::mem::ManuallyDrop::new(S));
-    /// ```
-    /// Use instead:
-    /// ```rust
-    /// struct S;
-    /// unsafe {
-    ///     std::mem::ManuallyDrop::drop(&mut std::mem::ManuallyDrop::new(S));
-    /// }
-    /// ```
-    #[clippy::version = "1.49.0"]
-    pub UNDROPPED_MANUALLY_DROPS,
-    correctness,
-    "use of safe `std::mem::drop` function to drop a std::mem::ManuallyDrop, which will not drop the inner value"
-}
-
 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`. \
@@ -84,7 +55,6 @@ const FORGET_NON_DROP_SUMMARY: &str = "call to `std::mem::forget` with a value t
 declare_lint_pass!(DropForgetRef => [
     DROP_NON_DROP,
     FORGET_NON_DROP,
-    UNDROPPED_MANUALLY_DROPS
 ]);
 
 impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
@@ -103,17 +73,7 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetRef {
                 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,
-                        UNDROPPED_MANUALLY_DROPS,
-                        expr.span,
-                        "the inner value of this ManuallyDrop will not be dropped",
-                        None,
-                        "to drop a `ManuallyDrop<T>`, use std::mem::ManuallyDrop::drop",
-                    );
-                    return;
-                }
+                sym::mem_drop if is_type_lang_item(cx, arg_ty, LangItem::ManuallyDrop) => return,
                 sym::mem_drop
                     if !(arg_ty.needs_drop(cx.tcx, cx.param_env)
                         || is_must_use_func_call(cx, arg)

src/tools/clippy/clippy_lints/src/renamed_lints.rs

@@ -50,6 +50,7 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::panic_params", "non_fmt_panics"),
     ("clippy::positional_named_format_parameters", "named_arguments_used_positionally"),
     ("clippy::temporary_cstring_as_ptr", "temporary_cstring_as_ptr"),
+    ("clippy::undropped_manually_drops", "undropped_manually_drops"),
     ("clippy::unknown_clippy_lints", "unknown_lints"),
     ("clippy::unused_label", "unused_labels"),
 ];

src/tools/clippy/tests/ui/rename.fixed

@@ -47,6 +47,7 @@
 #![allow(named_arguments_used_positionally)]
 #![allow(suspicious_double_ref_op)]
 #![allow(temporary_cstring_as_ptr)]
+#![allow(undropped_manually_drops)]
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
 #![warn(clippy::almost_complete_range)]
@@ -97,6 +98,7 @@
 #![warn(non_fmt_panics)]
 #![warn(named_arguments_used_positionally)]
 #![warn(temporary_cstring_as_ptr)]
+#![warn(undropped_manually_drops)]
 #![warn(unknown_lints)]
 #![warn(unused_labels)]
 

src/tools/clippy/tests/ui/rename.rs

@@ -47,6 +47,7 @@
 #![allow(named_arguments_used_positionally)]
 #![allow(suspicious_double_ref_op)]
 #![allow(temporary_cstring_as_ptr)]
+#![allow(undropped_manually_drops)]
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
 #![warn(clippy::almost_complete_letter_range)]
@@ -97,6 +98,7 @@
 #![warn(clippy::panic_params)]
 #![warn(clippy::positional_named_format_parameters)]
 #![warn(clippy::temporary_cstring_as_ptr)]
+#![warn(clippy::undropped_manually_drops)]
 #![warn(clippy::unknown_clippy_lints)]
 #![warn(clippy::unused_label)]