Rollup merge of #139535 - ChrisDenton:default-ptr, r=tgross35

Implement `Default` for raw pointers

ACP: https://github.com/rust-lang/libs-team/issues/571

This is instantly stable so we will need an FCP here.

Closes https://github.com/rust-lang/rfcs/issues/2464

3 files changed, 33 insertions, 0 deletions

diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index 0854e31c199..2d869958b85 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -1739,3 +1739,11 @@ impl<T: ?Sized> PartialOrd for *const T {
         *self >= *other
     }
 }
+
+#[stable(feature = "raw_ptr_default", since = "CURRENT_RUSTC_VERSION")]
+impl<T: ?Sized + Thin> Default for *const T {
+    /// Returns the default value of [`null()`][crate::ptr::null].
+    fn default() -> Self {
+        crate::ptr::null()
+    }
+}
diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index e29774963db..df49eedb350 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -2156,3 +2156,11 @@ impl<T: ?Sized> PartialOrd for *mut T {
         *self >= *other
     }
 }
+
+#[stable(feature = "raw_ptr_default", since = "CURRENT_RUSTC_VERSION")]
+impl<T: ?Sized + Thin> Default for *mut T {
+    /// Returns the default value of [`null_mut()`][crate::ptr::null_mut].
+    fn default() -> Self {
+        crate::ptr::null_mut()
+    }
+}
diff --git a/library/coretests/tests/ptr.rs b/library/coretests/tests/ptr.rs
index cc5f7946863..7d6e4eac1e2 100644
--- a/library/coretests/tests/ptr.rs
+++ b/library/coretests/tests/ptr.rs
@@ -1020,3 +1020,20 @@ fn test_ptr_swap_nonoverlapping_is_untyped() {
     ptr_swap_nonoverlapping_is_untyped_inner();
     const { ptr_swap_nonoverlapping_is_untyped_inner() };
 }
+
+#[test]
+fn test_ptr_default() {
+    #[derive(Default)]
+    struct PtrDefaultTest {
+        ptr: *const u64,
+    }
+    let default = PtrDefaultTest::default();
+    assert!(default.ptr.is_null());
+
+    #[derive(Default)]
+    struct PtrMutDefaultTest {
+        ptr: *mut u64,
+    }
+    let default = PtrMutDefaultTest::default();
+    assert!(default.ptr.is_null());
+}