1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
//! A lightweight version of [pin-project] written with declarative macros.
//!
//! # Examples
//!
//! [`pin_project!`] macro creates a projection type covering all the fields of struct.
//!
//! ```rust
//! use std::pin::Pin;
//!
//! use pin_project_lite::pin_project;
//!
//! pin_project! {
//!     struct Struct<T, U> {
//!         #[pin]
//!         pinned: T,
//!         unpinned: U,
//!     }
//! }
//!
//! impl<T, U> Struct<T, U> {
//!     fn method(self: Pin<&mut Self>) {
//!         let this = self.project();
//!         let _: Pin<&mut T> = this.pinned; // Pinned reference to the field
//!         let _: &mut U = this.unpinned; // Normal reference to the field
//!     }
//! }
//! ```
//!
//! # [pin-project] vs pin-project-lite
//!
//! Here are some similarities and differences compared to [pin-project].
//!
//! ## Similar: Safety
//!
//! pin-project-lite guarantees safety in much the same way as [pin-project]. Both are completely safe unless you write other unsafe code.
//!
//! ## Different: Minimal design
//!
//! This library does not tackle as expansive of a range of use cases as [pin-project] does. If your use case is not already covered, please use [pin-project].
//!
//! ## Different: No proc-macro related dependencies
//!
//! This is the **only** reason to use this crate. However, **if you already have proc-macro related dependencies in your crate's dependency graph, there is no benefit from using this crate.** (Note: There is almost no difference in the amount of code generated between [pin-project] and pin-project-lite.)
//!
//! ## Different: No useful error messages
//!
//! This macro does not handle any invalid input. So error messages are not to be useful in most cases. If you do need useful error messages, then upon error you can pass the same input to [pin-project] to receive a helpful description of the compile error.
//!
//! ## Different: Structs only
//!
//! pin-project-lite will refuse anything other than a braced struct with named fields. Enums and tuple structs are not supported.
//!
//! ## Different: No support for custom Drop implementation
//!
//! pin-project supports this by [`#[pinned_drop]`][pinned-drop].
//!
//! ## Different: No support for custom Unpin implementation
//!
//! pin-project supports this by [`UnsafeUnpin`][unsafe-unpin] and [`!Unpin`][not-unpin].
//!
//! ## Different: No support for pattern matching and destructing
//!
//! [pin-project supports this.][naming]
//!
//! [naming]: https://docs.rs/pin-project/1/pin_project/attr.pin_project.html
//! [not-unpin]: https://docs.rs/pin-project/1/pin_project/attr.pin_project.html#unpin
//! [pin-project]: https://github.com/taiki-e/pin-project
//! [pinned-drop]: https://docs.rs/pin-project/1/pin_project/attr.pin_project.html#pinned_drop
//! [unsafe-unpin]: https://docs.rs/pin-project/1/pin_project/attr.pin_project.html#unsafeunpin

#![no_std]
#![doc(test(
    no_crate_inject,
    attr(deny(warnings, rust_2018_idioms, single_use_lifetimes), allow(dead_code))
))]
#![warn(unsafe_code)]
#![warn(future_incompatible, rust_2018_idioms, single_use_lifetimes, unreachable_pub)]
#![warn(clippy::all, clippy::default_trait_access)]
// mem::take and #[non_exhaustive] requires Rust 1.40, matches! requires Rust 1.42
#![allow(
    clippy::mem_replace_with_default,
    clippy::manual_non_exhaustive,
    clippy::match_like_matches_macro
)]

/// A macro that creates a projection type covering all the fields of struct.
///
/// This macro creates a projection type according to the following rules:
///
/// * For the field that uses `#[pin]` attribute, makes the pinned reference to the field.
/// * For the other fields, makes the unpinned reference to the field.
///
/// And the following methods are implemented on the original type:
///
/// ```rust
/// # use std::pin::Pin;
/// # type Projection<'a> = &'a ();
/// # type ProjectionRef<'a> = &'a ();
/// # trait Dox {
/// fn project(self: Pin<&mut Self>) -> Projection<'_>;
/// fn project_ref(self: Pin<&Self>) -> ProjectionRef<'_>;
/// # }
/// ```
///
/// The visibility of the projected type and projection method is based on the
/// original type. However, if the visibility of the original type is `pub`,
/// the visibility of the projected type and the projection method is `pub(crate)`.
///
/// # Safety
///
/// `pin_project!` macro guarantees safety in much the same way as [pin-project] crate.
/// Both are completely safe unless you write other unsafe code.
///
/// See [pin-project] crate for more details.
///
/// # Examples
///
/// ```rust
/// use std::pin::Pin;
///
/// use pin_project_lite::pin_project;
///
/// pin_project! {
///     struct Struct<T, U> {
///         #[pin]
///         pinned: T,
///         unpinned: U,
///     }
/// }
///
/// impl<T, U> Struct<T, U> {
///     fn method(self: Pin<&mut Self>) {
///         let this = self.project();
///         let _: Pin<&mut T> = this.pinned; // Pinned reference to the field
///         let _: &mut U = this.unpinned; // Normal reference to the field
///     }
/// }
/// ```
///
/// If you want to call the `project()` method multiple times or later use the
/// original [`Pin`] type, it needs to use [`.as_mut()`][`Pin::as_mut`] to avoid
/// consuming the [`Pin`].
///
/// ```rust
/// use std::pin::Pin;
///
/// use pin_project_lite::pin_project;
///
/// pin_project! {
///     struct Struct<T> {
///         #[pin]
///         field: T,
///     }
/// }
///
/// impl<T> Struct<T> {
///     fn call_project_twice(mut self: Pin<&mut Self>) {
///         // `project` consumes `self`, so reborrow the `Pin<&mut Self>` via `as_mut`.
///         self.as_mut().project();
///         self.as_mut().project();
///     }
/// }
/// ```
///
/// # `!Unpin`
///
/// If you want to ensure that [`Unpin`] is not implemented, use `#[pin]`
/// attribute for a [`PhantomPinned`] field.
///
/// ```rust
/// use std::marker::PhantomPinned;
///
/// use pin_project_lite::pin_project;
///
/// pin_project! {
///     struct Struct<T> {
///         field: T,
///         #[pin] // <------ This `#[pin]` is required to make `Struct` to `!Unpin`.
///         _pin: PhantomPinned,
///     }
/// }
/// ```
///
/// Note that using [`PhantomPinned`] without `#[pin]` attribute has no effect.
///
/// [`PhantomPinned`]: core::marker::PhantomPinned
/// [`Pin::as_mut`]: core::pin::Pin::as_mut
/// [`Pin`]: core::pin::Pin
/// [pin-project]: https://github.com/taiki-e/pin-project
#[macro_export]
macro_rules! pin_project {
    ($($tt:tt)*) => {
        $crate::__pin_project_internal! { $($tt)* }
    };
}

// limitations:
// * no support for tuple structs and enums.
// * no support for naming the projection types.
// * no support for multiple trait/lifetime bounds.
// * no support for `Self` in where clauses. (wontfix)
// * no support for overlapping lifetime names. (wontfix)
// * no interoperability with other field attributes.
// * no useful error messages. (wontfix)
// etc...

// Not public API.
#[doc(hidden)]
#[macro_export]
macro_rules! __pin_project_internal {
    // =============================================================================================
    // main: struct
    (@struct_internal;
        [$proj_vis:vis]
        [$(#[$attrs:meta])* $vis:vis struct $ident:ident]
        [$($def_generics:tt)*]
        [$($impl_generics:tt)*] [$($ty_generics:tt)*] [$(where $($where_clause:tt)*)?]
        {
            $(
                $(#[$pin:ident])?
                $field_vis:vis $field:ident: $field_ty:ty
            ),+
        }
    ) => {
        $(#[$attrs])*
        $vis struct $ident $($def_generics)*
        $(where
            $($where_clause)*)?
        {
            $(
                $field_vis $field: $field_ty
            ),+
        }

        #[allow(explicit_outlives_requirements)]
        #[allow(single_use_lifetimes)] // https://github.com/rust-lang/rust/issues/55058
        #[allow(clippy::redundant_pub_crate)]
        #[allow(clippy::used_underscore_binding)]
        const _: () = {
            $crate::__pin_project_internal! { @make_proj_ty_struct;
                [$proj_vis]
                [$vis struct $ident]
                [$($impl_generics)*] [$($ty_generics)*] [$(where $($where_clause)*)?]
                {
                    $(
                        $(#[$pin])?
                        $field_vis $field: $field_ty
                    ),+
                }
            }

            impl <$($impl_generics)*> $ident <$($ty_generics)*>
            $(where
                $($where_clause)*)?
            {
                $proj_vis fn project<'__pin>(
                    self: $crate::__private::Pin<&'__pin mut Self>,
                ) -> Projection <'__pin, $($ty_generics)*> {
                    unsafe {
                        let Self { $($field),* } = self.get_unchecked_mut();
                        Projection {
                            $(
                                $field: $crate::__pin_project_internal!(@make_unsafe_field_proj;
                                    $(#[$pin])? $field
                                )
                            ),+
                        }
                    }
                }
                $proj_vis fn project_ref<'__pin>(
                    self: $crate::__private::Pin<&'__pin Self>,
                ) -> ProjectionRef <'__pin, $($ty_generics)*> {
                    unsafe {
                        let Self { $($field),* } = self.get_ref();
                        ProjectionRef {
                            $(
                                $field: $crate::__pin_project_internal!(@make_unsafe_field_proj;
                                    $(#[$pin])? $field
                                )
                            ),+
                        }
                    }
                }
            }

            $crate::__pin_project_internal! { @make_unpin_impl;
                [$vis $ident]
                [$($impl_generics)*] [$($ty_generics)*] [$(where $($where_clause)*)?]
                $(
                    $field: $crate::__pin_project_internal!(@make_unpin_bound;
                        $(#[$pin])? $field_ty
                    )
                ),+
            }

            $crate::__pin_project_internal! { @make_drop_impl;
                [$ident]
                [$($impl_generics)*] [$($ty_generics)*] [$(where $($where_clause)*)?]
            }

            // Ensure that it's impossible to use pin projections on a #[repr(packed)] struct.
            //
            // Taking a reference to a packed field is UB, and applying
            // `#[forbid(unaligned_references)]` makes sure that doing this is a hard error.
            //
            // If the struct ends up having #[repr(packed)] applied somehow,
            // this will generate an (unfriendly) error message. Under all reasonable
            // circumstances, we'll detect the #[repr(packed)] attribute, and generate
            // a much nicer error above.
            //
            // See https://github.com/taiki-e/pin-project/pull/34 for more details.
            //
            // Note:
            // - Lint-based tricks aren't perfect, but they're much better than nothing:
            //   https://github.com/taiki-e/pin-project-lite/issues/26
            //
            // - Enable both unaligned_references and safe_packed_borrows lints
            //   because unaligned_references lint does not exist in older compilers:
            //   https://github.com/taiki-e/pin-project-lite/pull/55
            //   https://github.com/rust-lang/rust/pull/82525
            #[forbid(unaligned_references, safe_packed_borrows)]
            fn __assert_not_repr_packed <$($impl_generics)*> (this: &$ident <$($ty_generics)*>)
            $(where
                $($where_clause)*)?
            {
                $(
                    let _ = &this.$field;
                )+
            }
        };
    };

    // =============================================================================================
    // make_proj_ty: struct
    (@make_proj_ty_struct;
        [$proj_vis:vis]
        [$vis:vis struct $ident:ident]
        [$($impl_generics:tt)*] [$($ty_generics:tt)*] [$(where $($where_clause:tt)* )?]
        {
            $(
                $(#[$pin:ident])?
                $field_vis:vis $field:ident: $field_ty:ty
            ),+
        }
    ) => {
        #[allow(dead_code)] // This lint warns unused fields/variants.
        #[allow(clippy::mut_mut)] // This lint warns `&mut &mut <ty>`.
        #[allow(clippy::type_repetition_in_bounds)] // https://github.com/rust-lang/rust-clippy/issues/4326
        $proj_vis struct Projection <'__pin, $($impl_generics)*>
        where
            $ident <$($ty_generics)*>: '__pin
            $(, $($where_clause)*)?
        {
            $(
                $field_vis $field: $crate::__pin_project_internal!(@make_proj_field;
                    $(#[$pin])? $field_ty; mut
                )
            ),+
        }
        #[allow(dead_code)] // This lint warns unused fields/variants.
        #[allow(clippy::type_repetition_in_bounds)] // https://github.com/rust-lang/rust-clippy/issues/4326
        $proj_vis struct ProjectionRef <'__pin, $($impl_generics)*>
        where
            $ident <$($ty_generics)*>: '__pin
            $(, $($where_clause)*)?
        {
            $(
                $field_vis $field: $crate::__pin_project_internal!(@make_proj_field;
                    $(#[$pin])? $field_ty;
                )
            ),+
        }
    };

    // =============================================================================================
    // make_unpin_impl
    (@make_unpin_impl;
        [$vis:vis $ident:ident]
        [$($impl_generics:tt)*] [$($ty_generics:tt)*] [$(where $($where_clause:tt)* )?]
        $($field:tt)*
    ) => {
        // Automatically create the appropriate conditional `Unpin` implementation.
        //
        // Basically this is equivalent to the following code:
        // ```rust
        // impl<T, U> Unpin for Struct<T, U> where T: Unpin {}
        // ```
        //
        // However, if struct is public and there is a private type field,
        // this would cause an E0446 (private type in public interface).
        //
        // When RFC 2145 is implemented (rust-lang/rust#48054),
        // this will become a lint, rather then a hard error.
        //
        // As a workaround for this, we generate a new struct, containing all of the pinned
        // fields from our #[pin_project] type. This struct is delcared within
        // a function, which makes it impossible to be named by user code.
        // This guarnatees that it will use the default auto-trait impl for Unpin -
        // that is, it will implement Unpin iff all of its fields implement Unpin.
        // This type can be safely declared as 'public', satisfiying the privacy
        // checker without actually allowing user code to access it.
        //
        // This allows users to apply the #[pin_project] attribute to types
        // regardless of the privacy of the types of their fields.
        //
        // See also https://github.com/taiki-e/pin-project/pull/53.
        $vis struct __Origin <'__pin, $($impl_generics)*>
        $(where
            $($where_clause)*)?
        {
            __dummy_lifetime: $crate::__private::PhantomData<&'__pin ()>,
            $($field)*
        }
        impl <'__pin, $($impl_generics)*> $crate::__private::Unpin for $ident <$($ty_generics)*>
        where
            __Origin <'__pin, $($ty_generics)*>: $crate::__private::Unpin
            $(, $($where_clause)*)?
        {
        }
    };

    // =============================================================================================
    // make_drop_impl
    (@make_drop_impl;
        [$ident:ident]
        [$($impl_generics:tt)*] [$($ty_generics:tt)*] [$(where $($where_clause:tt)* )?]
    ) => {
        // Ensure that struct does not implement `Drop`.
        //
        // There are two possible cases:
        // 1. The user type does not implement Drop. In this case,
        // the first blanked impl will not apply to it. This code
        // will compile, as there is only one impl of MustNotImplDrop for the user type
        // 2. The user type does impl Drop. This will make the blanket impl applicable,
        // which will then comflict with the explicit MustNotImplDrop impl below.
        // This will result in a compilation error, which is exactly what we want.
        trait MustNotImplDrop {}
        #[allow(clippy::drop_bounds, drop_bounds)]
        impl<T: $crate::__private::Drop> MustNotImplDrop for T {}
        impl <$($impl_generics)*> MustNotImplDrop for $ident <$($ty_generics)*>
        $(where
            $($where_clause)*)?
        {
        }
    };

    // =============================================================================================
    // make_unpin_bound
    (@make_unpin_bound;
        #[pin]
        $field_ty:ty
    ) => {
        $field_ty
    };
    (@make_unpin_bound;
        $field_ty:ty
    ) => {
        $crate::__private::AlwaysUnpin<$field_ty>
    };

    // =============================================================================================
    // make_unsafe_field_proj
    (@make_unsafe_field_proj;
        #[pin]
        $field:ident
    ) => {
        $crate::__private::Pin::new_unchecked($field)
    };
    (@make_unsafe_field_proj;
        $field:ident
    ) => {
        $field
    };

    // =============================================================================================
    // make_proj_field
    (@make_proj_field;
        #[pin]
        $field_ty:ty;
        $($mut:ident)?
    ) => {
        $crate::__private::Pin<&'__pin $($mut)? ($field_ty)>
    };
    (@make_proj_field;
        $field_ty:ty;
        $($mut:ident)?
    ) => {
        &'__pin $($mut)? ($field_ty)
    };

    // =============================================================================================
    // Parses input and determines visibility
    (
        $(#[$attrs:meta])*
        pub struct $ident:ident $(<
            $( $lifetime:lifetime $(: $lifetime_bound:lifetime)? ),* $(,)?
            $( $generics:ident
                $(: $generics_bound:path)?
                $(: ?$generics_unsized_bound:path)?
                $(: $generics_lifetime_bound:lifetime)?
                $(= $generics_default:ty)?
            ),* $(,)?
        >)?
        $(where
            $( $where_clause_ty:ty
                $(: $where_clause_bound:path)?
                $(: ?$where_clause_unsized_bound:path)?
                $(: $where_clause_lifetime_bound:lifetime)?
            ),* $(,)?
        )?
        {
            $(
                $(#[$pin:ident])?
                $field_vis:vis $field:ident: $field_ty:ty
            ),+ $(,)?
        }
    ) => {
        $crate::__pin_project_internal! { @struct_internal;
            [pub(crate)]
            [$(#[$attrs])* pub struct $ident]
            [$(<
                $( $lifetime $(: $lifetime_bound)? ,)*
                $( $generics
                    $(: $generics_bound)?
                    $(: ?$generics_unsized_bound)?
                    $(: $generics_lifetime_bound)?
                    $(= $generics_default)?
                ),*
            >)?]
            [$(
                $( $lifetime $(: $lifetime_bound)? ,)*
                $( $generics
                    $(: $generics_bound)?
                    $(: ?$generics_unsized_bound)?
                    $(: $generics_lifetime_bound)?
                ),*
            )?]
            [$( $( $lifetime ,)* $( $generics ),* )?]
            [$(where $( $where_clause_ty
                $(: $where_clause_bound)?
                $(: ?$where_clause_unsized_bound)?
                $(: $where_clause_lifetime_bound)?
            ),* )?]
            {
                $(
                    $(#[$pin])?
                    $field_vis $field: $field_ty
                ),+
            }
        }
    };
    (
        $(#[$attrs:meta])*
        $vis:vis struct $ident:ident $(<
            $( $lifetime:lifetime $(: $lifetime_bound:lifetime)? ),* $(,)?
            $( $generics:ident
                $(: $generics_bound:path)?
                $(: ?$generics_unsized_bound:path)?
                $(: $generics_lifetime_bound:lifetime)?
                $(= $generics_default:ty)?
            ),* $(,)?
        >)?
        $(where
            $( $where_clause_ty:ty
                $(: $where_clause_bound:path)?
                $(: ?$where_clause_unsized_bound:path)?
                $(: $where_clause_lifetime_bound:lifetime)?
            ),* $(,)?
        )?
        {
            $(
                $(#[$pin:ident])?
                $field_vis:vis $field:ident: $field_ty:ty
            ),+ $(,)?
        }
    ) => {
        $crate::__pin_project_internal! { @struct_internal;
            [$vis]
            [$(#[$attrs])* $vis struct $ident]
            [$(<
                $( $lifetime $(: $lifetime_bound)? ,)*
                $( $generics
                    $(: $generics_bound)?
                    $(: ?$generics_unsized_bound)?
                    $(: $generics_lifetime_bound)?
                    $(= $generics_default)?
                ),*
            >)?]
            [$(
                $( $lifetime $(: $lifetime_bound)? ,)*
                $( $generics
                    $(: $generics_bound)?
                    $(: ?$generics_unsized_bound)?
                    $(: $generics_lifetime_bound)?
                ),*
            )?]
            [$( $( $lifetime ,)* $( $generics ),* )?]
            [$(where $( $where_clause_ty
                $(: $where_clause_bound)?
                $(: ?$where_clause_unsized_bound)?
                $(: $where_clause_lifetime_bound)?
            ),* )?]
            {
                $(
                    $(#[$pin])?
                    $field_vis $field: $field_ty
                ),+
            }
        }
    };
}

// Not public API.
#[doc(hidden)]
pub mod __private {
    #[doc(hidden)]
    pub use core::{
        marker::{PhantomData, Unpin},
        ops::Drop,
        pin::Pin,
    };

    // This is an internal helper struct used by `pin_project!`.
    #[doc(hidden)]
    pub struct AlwaysUnpin<T: ?Sized>(PhantomData<T>);

    impl<T: ?Sized> Unpin for AlwaysUnpin<T> {}
}