Auto merge of #89144 - sexxi-goose:insig_stdlib, r=nikomatsakis

2229: Mark insignificant dtor in stdlib

I looked at all public [stdlib Drop implementations](https://doc.rust-lang.org/stable/std/ops/trait.Drop.html#implementors) and categorized them into Insigificant/Maybe/Significant Drop.

Reasons are noted here: https://docs.google.com/spreadsheets/d/19edb9r5lo2UqMrCOVjV0fwcSdS-R7qvKNL76q7tO8VA/edit#gid=1838773501

One thing missing from this PR is tagging HashMap as insigificant destructor as that needs some discussion.

r? `@Mark-Simulacrum`

cc `@nikomatsakis`

6 files changed, 7 insertions, 0 deletions

diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index 2a7e1ef351b..3b7c92818f6 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -155,6 +155,7 @@ pub(super) const MIN_LEN: usize = node::MIN_LEN_AFTER_SPLIT;
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "BTreeMap")]
+#[rustc_insignificant_dtor]
 pub struct BTreeMap<K, V> {
     root: Option<Root<K, V>>,
     length: usize,
@@ -331,6 +332,7 @@ impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IterMut<'_, K, V> {
 /// [`into_iter`]: IntoIterator::into_iter
 /// [`IntoIterator`]: core::iter::IntoIterator
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_insignificant_dtor]
 pub struct IntoIter<K, V> {
     range: LazyLeafRange<marker::Dying, K, V>,
     length: usize,
diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
index 0b60c2aa9f6..a769c558b4f 100644
--- a/library/alloc/src/collections/linked_list.rs
+++ b/library/alloc/src/collections/linked_list.rs
@@ -46,6 +46,7 @@ mod tests;
 /// [`VecDeque`]: super::vec_deque::VecDeque
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "LinkedList")]
+#[rustc_insignificant_dtor]
 pub struct LinkedList<T> {
     head: Option<NonNull<Node<T>>>,
     tail: Option<NonNull<Node<T>>>,
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index 10144cc17bf..cae0f29af83 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -90,6 +90,7 @@ const MAXIMUM_ZST_CAPACITY: usize = 1 << (usize::BITS - 1); // Largest possible
 /// [`make_contiguous`]: VecDeque::make_contiguous
 #[cfg_attr(not(test), rustc_diagnostic_item = "vecdeque_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_insignificant_dtor]
 pub struct VecDeque<
     T,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 3648271c620..81e97805a72 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -305,6 +305,7 @@ struct RcBox<T: ?Sized> {
 /// [get_mut]: Rc::get_mut
 #[cfg_attr(not(test), rustc_diagnostic_item = "Rc")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_insignificant_dtor]
 pub struct Rc<T: ?Sized> {
     ptr: NonNull<RcBox<T>>,
     phantom: PhantomData<RcBox<T>>,
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 0bd152f17a6..4cb0a4b10bd 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -22,6 +22,7 @@ use core::slice::{self};
 /// let iter: std::vec::IntoIter<_> = v.into_iter();
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_insignificant_dtor]
 pub struct IntoIter<
     T,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 4440b1f599f..c37ec375561 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -396,6 +396,7 @@ mod spec_extend;
 /// [owned slice]: Box
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "vec_type")]
+#[rustc_insignificant_dtor]
 pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
     buf: RawVec<T, A>,
     len: usize,