Add TryPinInitWrapper trait.

Implement it for `UnsafeCell` and `UnsafePinned` (unsafe-pinned feature is enabled.

Signed-off-by: Christian Schrefl <chrisi.schrefl@gmail.com>

Author: onestacked

Cargo.toml

@@ -21,6 +21,7 @@ pin-init-internal = { path = "./internal", version = "=0.0.5" }
 default = ["std", "alloc"]
 std = []
 alloc = []
+unsafe-pinned = []
 
 [build-dependencies]
 rustc_version = "0.4"
@@ -34,7 +35,11 @@ prettyplease = { version = "0.2", features = ["verbatim"] }
 
 [lints.rust]
 non_ascii_idents = "deny"
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(NO_UI_TESTS)', 'cfg(NO_ALLOC_FAIL_TESTS)', 'cfg(kernel)'] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+    'cfg(NO_UI_TESTS)',
+    'cfg(NO_ALLOC_FAIL_TESTS)',
+    'cfg(kernel)',
+] }
 unsafe_op_in_unsafe_fn = "deny"
 unused_attributes = "deny"
 warnings = "deny"

src/lib.rs

@@ -269,6 +269,7 @@
 #![forbid(missing_docs, unsafe_op_in_unsafe_fn)]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(feature = "alloc", feature(allocator_api))]
+#![cfg_attr(feature = "unsafe-pinned", feature(unsafe_pinned))]
 
 use core::{
     cell::UnsafeCell,
@@ -1481,3 +1482,30 @@ macro_rules! impl_tuple_zeroable {
 }
 
 impl_tuple_zeroable!(A, B, C, D, E, F, G, H, I, J);
+
+/// Trait for creating a [PinInitialized](PinInit) wrapper containing `T`.
+pub trait TryPinInitWrapper<T: ?Sized> {
+    /// Create an pin-initializer for a [`Self`] containing `T` form the `value` initializer.
+    fn try_pin_init<E>(value: impl PinInit<T, E>) -> impl PinInit<Self, E>;
+}
+
+impl<T: ?Sized> TryPinInitWrapper<T> for UnsafeCell<T> {
+    fn try_pin_init<E>(value: impl PinInit<T, E>) -> impl PinInit<Self, E> {
+        // SAFETY:
+        //   - In case of an error in `value` the error is returned, otherwise `slot` is fully
+        //     initialized, since `self.value` is initialized and `_pin` is a zero sized type.
+        //   - The `Pin` invariants of `self.value` are upheld, since no moving occurs.
+        unsafe { pin_init_from_closure(move |slot| value.__pinned_init(Self::raw_get(slot))) }
+    }
+}
+
+#[cfg(feature = "unsafe-pinned")]
+impl<T: ?Sized> TryPinInitWrapper<T> for core::pin::UnsafePinned<T> {
+    fn try_pin_init<E>(value: impl PinInit<T, E>) -> impl PinInit<Self, E> {
+        // SAFETY:
+        //   - In case of an error in `value` the error is returned, otherwise `slot` is fully
+        //     initialized, since `self.value` is initialized and `_pin` is a zero sized type.
+        //   - The `Pin` invariants of `self.value` are upheld, since no moving occurs.
+        unsafe { pin_init_from_closure(move |slot| value.__pinned_init(Self::raw_get_mut(slot))) }
+    }
+}