Auto merge of #42527 - qnighy:unsized-tuple-coercions, r=arielb1

Unsized tuple coercions

Part of #18469. Fixes #32702.

#37685 and #34451 might also be related.

This PR does the following:

- Introduce explicit `Sized` constraints on tuple initializers, similar to that of record-struct initializers. Not much relevant to the main contribution but I noticed this when making tests for unsized tuple coercions.
- Implement `(.., T): Unsize<(.., U)>` where `T: Unsize<U>`.
- Assume `(.., T)` is MaybeUnsizedUnivariant.
- Modify `src/librustc/ty/util.rs` and `src/librustc_trans/glue.rs` so that tuples and structs are uniformly traversed when translating.

src/test/compile-fail/dst-bad-assign-3.rs

@@ -0,0 +1,50 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Forbid assignment into a dynamically sized type.
+
+#![feature(unsized_tuple_coercion)]
+
+type Fat<T: ?Sized> = (isize, &'static str, T);
+//~^ WARNING trait bounds are not (yet) enforced
+
+#[derive(PartialEq,Eq)]
+struct Bar;
+
+#[derive(PartialEq,Eq)]
+struct Bar1 {
+    f: isize
+}
+
+trait ToBar {
+    fn to_bar(&self) -> Bar;
+    fn to_val(&self) -> isize;
+}
+
+impl ToBar for Bar1 {
+    fn to_bar(&self) -> Bar {
+        Bar
+    }
+    fn to_val(&self) -> isize {
+        self.f
+    }
+}
+
+pub fn main() {
+    // Assignment.
+    let f5: &mut Fat<ToBar> = &mut (5, "some str", Bar1 {f :42});
+    let z: Box<ToBar> = Box::new(Bar1 {f: 36});
+    f5.2 = Bar1 {f: 36};
+    //~^ ERROR mismatched types
+    //~| expected type `ToBar`
+    //~| found type `Bar1`
+    //~| expected trait ToBar, found struct `Bar1`
+    //~| ERROR `ToBar: std::marker::Sized` is not satisfied
+}

src/test/compile-fail/dst-bad-coerce1.rs

@@ -10,6 +10,8 @@
 
 // Attempt to change the type as well as unsizing.
 
+#![feature(unsized_tuple_coercion)]
+
 struct Fat<T: ?Sized> {
     ptr: T
 }
@@ -29,4 +31,16 @@ pub fn main() {
     let f2: &Fat<Foo> = &f1;
     let f3: &Fat<Bar> = f2;
     //~^ ERROR `Foo: Bar` is not satisfied
+
+    // Tuple with a vec of isize.
+    let f1 = ([1, 2, 3],);
+    let f2: &([isize; 3],) = &f1;
+    let f3: &([usize],) = f2;
+    //~^ ERROR mismatched types
+
+    // Tuple with a trait.
+    let f1 = (Foo,);
+    let f2: &(Foo,) = &f1;
+    let f3: &(Bar,) = f2;
+    //~^ ERROR `Foo: Bar` is not satisfied
 }

src/test/compile-fail/dst-bad-coerce2.rs

@@ -28,4 +28,14 @@ pub fn main() {
     let f1 = Fat { ptr: Foo };
     let f2: &Fat<Foo> = &f1;
     let f3: &mut Fat<Bar> = f2; //~ ERROR mismatched types
+
+    // Tuple with a vec of ints.
+    let f1 = ([1, 2, 3],);
+    let f2: &([isize; 3],) = &f1;
+    let f3: &mut ([isize],) = f2; //~ ERROR mismatched types
+
+    // Tuple with a trait.
+    let f1 = (Foo,);
+    let f2: &(Foo,) = &f1;
+    let f3: &mut (Bar,) = f2; //~ ERROR mismatched types
 }

src/test/compile-fail/dst-bad-coerce3.rs

@@ -10,6 +10,8 @@
 
 // Attempt to extend the lifetime as well as unsizing.
 
+#![feature(unsized_tuple_coercion)]
+
 struct Fat<T: ?Sized> {
     ptr: T
 }
@@ -28,6 +30,16 @@ fn baz<'a>() {
     let f1 = Fat { ptr: Foo };
     let f2: &Fat<Foo> = &f1; //~ ERROR `f1` does not live long enough
     let f3: &'a Fat<Bar> = f2;
+
+    // Tuple with a vec of ints.
+    let f1 = ([1, 2, 3],);
+    let f2: &([isize; 3],) = &f1; //~ ERROR `f1` does not live long enough
+    let f3: &'a ([isize],) = f2;
+
+    // Tuple with a trait.
+    let f1 = (Foo,);
+    let f2: &(Foo,) = &f1; //~ ERROR `f1` does not live long enough
+    let f3: &'a (Bar,) = f2;
 }
 
 pub fn main() {

src/test/compile-fail/dst-bad-coerce4.rs

@@ -10,6 +10,8 @@
 
 // Attempt to coerce from unsized to sized.
 
+#![feature(unsized_tuple_coercion)]
+
 struct Fat<T: ?Sized> {
     ptr: T
 }
@@ -22,4 +24,12 @@ pub fn main() {
     //~| expected type `&Fat<[isize; 3]>`
     //~| found type `&Fat<[isize]>`
     //~| expected array of 3 elements, found slice
+
+    // Tuple with a vec of isizes.
+    let f1: &([isize],) = &([1, 2, 3],);
+    let f2: &([isize; 3],) = f1;
+    //~^ ERROR mismatched types
+    //~| expected type `&([isize; 3],)`
+    //~| found type `&([isize],)`
+    //~| expected array of 3 elements, found slice
 }

src/test/compile-fail/dst-bad-deep-2.rs

@@ -0,0 +1,23 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Try to initialise a DST struct where the lost information is deeply nested.
+// This is an error because it requires an unsized rvalue. This is a problem
+// because it would require stack allocation of an unsized temporary (*g in the
+// test).
+
+#![feature(unsized_tuple_coercion)]
+
+pub fn main() {
+    let f: ([isize; 3],) = ([5, 6, 7],);
+    let g: &([isize],) = &f;
+    let h: &(([isize],),) = &(*g,);
+    //~^ ERROR `[isize]: std::marker::Sized` is not satisfied
+}

src/test/compile-fail/feature-gate-unsized_tuple_coercion.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let _ : &(Send,) = &((),);
+    //~^ ERROR Unsized tuple coercion is not stable enough
+}

src/test/compile-fail/unsized3.rs

@@ -54,6 +54,7 @@ fn f9<X: ?Sized>(x1: Box<S<X>>) {
 fn f10<X: ?Sized>(x1: Box<S<X>>) {
     f5(&(32, *x1));
     //~^ ERROR `X: std::marker::Sized` is not satisfied
+    //~| ERROR `X: std::marker::Sized` is not satisfied
 }
 
 pub fn main() {

src/test/run-pass-valgrind/dst-dtor-3.rs

@@ -0,0 +1,34 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// no-prefer-dynamic
+
+#![feature(unsized_tuple_coercion)]
+
+static mut DROP_RAN: bool = false;
+
+struct Foo;
+impl Drop for Foo {
+    fn drop(&mut self) {
+        unsafe { DROP_RAN = true; }
+    }
+}
+
+trait Trait { fn dummy(&self) { } }
+impl Trait for Foo {}
+
+pub fn main() {
+    {
+        let _x: Box<(i32, Trait)> = Box::<(i32, Foo)>::new((42, Foo));
+    }
+    unsafe {
+        assert!(DROP_RAN);
+    }
+}

src/test/run-pass-valgrind/dst-dtor-4.rs

@@ -0,0 +1,31 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// no-prefer-dynamic
+
+#![feature(unsized_tuple_coercion)]
+
+static mut DROP_RAN: isize = 0;
+
+struct Foo;
+impl Drop for Foo {
+    fn drop(&mut self) {
+        unsafe { DROP_RAN += 1; }
+    }
+}
+
+pub fn main() {
+    {
+        let _x: Box<(i32, [Foo])> = Box::<(i32, [Foo; 3])>::new((42, [Foo, Foo, Foo]));
+    }
+    unsafe {
+        assert_eq!(DROP_RAN, 3);
+    }
+}

src/test/run-pass/dst-irrefutable-bind.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsized_tuple_coercion)]
+
 struct Test<T: ?Sized>(T);
 
 fn main() {
@@ -21,4 +23,14 @@ fn main() {
     let slice = &[1,2,3];
     let x = Test(&slice);
     let Test(&_slice) = x;
+
+
+    let x = (10, [1,2,3]);
+    let x : &(i32, [i32]) = &x;
+
+    let & ref _y = x;
+
+    let slice = &[1,2,3];
+    let x = (10, &slice);
+    let (_, &_slice) = x;
 }

src/test/run-pass/dst-raw.rs

@@ -11,6 +11,8 @@
 // Test DST raw pointers
 
 
+#![feature(unsized_tuple_coercion)]
+
 trait Trait {
     fn foo(&self) -> isize;
 }
@@ -45,6 +47,14 @@ pub fn main() {
     };
     assert_eq!(r, 42);
 
+    // raw DST tuple
+    let p = (A { f: 42 },);
+    let o: *const (Trait,) = &p;
+    let r = unsafe {
+        (&*o).0.foo()
+    };
+    assert_eq!(r, 42);
+
     // raw slice
     let a: *const [_] = &[1, 2, 3];
     unsafe {
@@ -72,6 +82,15 @@ pub fn main() {
         assert_eq!(len, 3);
     }
 
+    // raw DST tuple with slice
+    let c: *const ([_],) = &([1, 2, 3],);
+    unsafe {
+        let b = (&*c).0[0];
+        assert_eq!(b, 1);
+        let len = (&*c).0.len();
+        assert_eq!(len, 3);
+    }
+
     // all of the above with *mut
     let mut x = A { f: 42 };
     let z: *mut Trait = &mut x;
@@ -87,6 +106,13 @@ pub fn main() {
     };
     assert_eq!(r, 42);
 
+    let mut p = (A { f: 42 },);
+    let o: *mut (Trait,) = &mut p;
+    let r = unsafe {
+        (&*o).0.foo()
+    };
+    assert_eq!(r, 42);
+
     let a: *mut [_] = &mut [1, 2, 3];
     unsafe {
         let b = (*a)[2];
@@ -110,4 +136,12 @@ pub fn main() {
         let len = (&*c).f.len();
         assert_eq!(len, 3);
     }
+
+    let c: *mut ([_],) = &mut ([1, 2, 3],);
+    unsafe {
+        let b = (&*c).0[0];
+        assert_eq!(b, 1);
+        let len = (&*c).0.len();
+        assert_eq!(len, 3);
+    }
 }

src/test/run-pass/dst-trait-tuple.rs

@@ -0,0 +1,111 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+#![allow(unused_features)]
+#![feature(box_syntax)]
+#![feature(unsized_tuple_coercion)]
+
+type Fat<T: ?Sized> = (isize, &'static str, T);
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+struct Bar;
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+struct Bar1 {
+    f: isize
+}
+
+trait ToBar {
+    fn to_bar(&self) -> Bar;
+    fn to_val(&self) -> isize;
+}
+
+impl ToBar for Bar {
+    fn to_bar(&self) -> Bar {
+        *self
+    }
+    fn to_val(&self) -> isize {
+        0
+    }
+}
+impl ToBar for Bar1 {
+    fn to_bar(&self) -> Bar {
+        Bar
+    }
+    fn to_val(&self) -> isize {
+        self.f
+    }
+}
+
+// x is a fat pointer
+fn foo(x: &Fat<ToBar>) {
+    assert_eq!(x.0, 5);
+    assert_eq!(x.1, "some str");
+    assert_eq!(x.2.to_bar(), Bar);
+    assert_eq!(x.2.to_val(), 42);
+
+    let y = &x.2;
+    assert_eq!(y.to_bar(), Bar);
+    assert_eq!(y.to_val(), 42);
+}
+
+fn bar(x: &ToBar) {
+    assert_eq!(x.to_bar(), Bar);
+    assert_eq!(x.to_val(), 42);
+}
+
+fn baz(x: &Fat<Fat<ToBar>>) {
+    assert_eq!(x.0, 5);
+    assert_eq!(x.1, "some str");
+    assert_eq!((x.2).0, 8);
+    assert_eq!((x.2).1, "deep str");
+    assert_eq!((x.2).2.to_bar(), Bar);
+    assert_eq!((x.2).2.to_val(), 42);
+
+    let y = &(x.2).2;
+    assert_eq!(y.to_bar(), Bar);
+    assert_eq!(y.to_val(), 42);
+
+}
+
+pub fn main() {
+    let f1 = (5, "some str", Bar1 {f :42});
+    foo(&f1);
+    let f2 = &f1;
+    foo(f2);
+    let f3: &Fat<ToBar> = f2;
+    foo(f3);
+    let f4: &Fat<ToBar> = &f1;
+    foo(f4);
+    let f5: &Fat<ToBar> = &(5, "some str", Bar1 {f :42});
+    foo(f5);
+
+    // Zero size object.
+    let f6: &Fat<ToBar> = &(5, "some str", Bar);
+    assert_eq!(f6.2.to_bar(), Bar);
+
+    // &*
+    //
+    let f7: Box<ToBar> = Box::new(Bar1 {f :42});
+    bar(&*f7);
+
+    // Deep nesting
+    let f1 = (5, "some str", (8, "deep str", Bar1 {f :42}));
+    baz(&f1);
+    let f2 = &f1;
+    baz(f2);
+    let f3: &Fat<Fat<ToBar>> = f2;
+    baz(f3);
+    let f4: &Fat<Fat<ToBar>> = &f1;
+    baz(f4);
+    let f5: &Fat<Fat<ToBar>> = &(5, "some str", (8, "deep str", Bar1 {f :42}));
+    baz(f5);
+}

src/test/run-pass/dst-tuple-sole.rs

@@ -0,0 +1,85 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// As dst-tuple.rs, but the unsized field is the only field in the tuple.
+
+
+#![feature(unsized_tuple_coercion)]
+
+type Fat<T: ?Sized> = (T,);
+
+// x is a fat pointer
+fn foo(x: &Fat<[isize]>) {
+    let y = &x.0;
+    assert_eq!(x.0.len(), 3);
+    assert_eq!(y[0], 1);
+    assert_eq!(x.0[1], 2);
+}
+
+fn foo2<T:ToBar>(x: &Fat<[T]>) {
+    let y = &x.0;
+    let bar = Bar;
+    assert_eq!(x.0.len(), 3);
+    assert_eq!(y[0].to_bar(), bar);
+    assert_eq!(x.0[1].to_bar(), bar);
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+struct Bar;
+
+trait ToBar {
+    fn to_bar(&self) -> Bar;
+}
+
+impl ToBar for Bar {
+    fn to_bar(&self) -> Bar {
+        *self
+    }
+}
+
+pub fn main() {
+    // With a vec of ints.
+    let f1 = ([1, 2, 3],);
+    foo(&f1);
+    let f2 = &f1;
+    foo(f2);
+    let f3: &Fat<[isize]> = f2;
+    foo(f3);
+    let f4: &Fat<[isize]> = &f1;
+    foo(f4);
+    let f5: &Fat<[isize]> = &([1, 2, 3],);
+    foo(f5);
+
+    // With a vec of Bars.
+    let bar = Bar;
+    let f1 = ([bar, bar, bar],);
+    foo2(&f1);
+    let f2 = &f1;
+    foo2(f2);
+    let f3: &Fat<[Bar]> = f2;
+    foo2(f3);
+    let f4: &Fat<[Bar]> = &f1;
+    foo2(f4);
+    let f5: &Fat<[Bar]> = &([bar, bar, bar],);
+    foo2(f5);
+
+    // Assignment.
+    let f5: &mut Fat<[isize]> = &mut ([1, 2, 3],);
+    f5.0[1] = 34;
+    assert_eq!(f5.0[0], 1);
+    assert_eq!(f5.0[1], 34);
+    assert_eq!(f5.0[2], 3);
+
+    // Zero size vec.
+    let f5: &Fat<[isize]> = &([],);
+    assert!(f5.0.is_empty());
+    let f5: &Fat<[Bar]> = &([],);
+    assert!(f5.0.is_empty());
+}

src/test/run-pass/dst-tuple.rs

@@ -0,0 +1,129 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+#![allow(unknown_features)]
+#![feature(box_syntax)]
+#![feature(unsized_tuple_coercion)]
+
+type Fat<T: ?Sized> = (isize, &'static str, T);
+
+// x is a fat pointer
+fn foo(x: &Fat<[isize]>) {
+    let y = &x.2;
+    assert_eq!(x.2.len(), 3);
+    assert_eq!(y[0], 1);
+    assert_eq!(x.2[1], 2);
+    assert_eq!(x.0, 5);
+    assert_eq!(x.1, "some str");
+}
+
+fn foo2<T:ToBar>(x: &Fat<[T]>) {
+    let y = &x.2;
+    let bar = Bar;
+    assert_eq!(x.2.len(), 3);
+    assert_eq!(y[0].to_bar(), bar);
+    assert_eq!(x.2[1].to_bar(), bar);
+    assert_eq!(x.0, 5);
+    assert_eq!(x.1, "some str");
+}
+
+fn foo3(x: &Fat<Fat<[isize]>>) {
+    let y = &(x.2).2;
+    assert_eq!(x.0, 5);
+    assert_eq!(x.1, "some str");
+    assert_eq!((x.2).0, 8);
+    assert_eq!((x.2).1, "deep str");
+    assert_eq!((x.2).2.len(), 3);
+    assert_eq!(y[0], 1);
+    assert_eq!((x.2).2[1], 2);
+}
+
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+struct Bar;
+
+trait ToBar {
+    fn to_bar(&self) -> Bar;
+}
+
+impl ToBar for Bar {
+    fn to_bar(&self) -> Bar {
+        *self
+    }
+}
+
+pub fn main() {
+    // With a vec of ints.
+    let f1 = (5, "some str", [1, 2, 3]);
+    foo(&f1);
+    let f2 = &f1;
+    foo(f2);
+    let f3: &Fat<[isize]> = f2;
+    foo(f3);
+    let f4: &Fat<[isize]> = &f1;
+    foo(f4);
+    let f5: &Fat<[isize]> = &(5, "some str", [1, 2, 3]);
+    foo(f5);
+
+    // With a vec of Bars.
+    let bar = Bar;
+    let f1 = (5, "some str", [bar, bar, bar]);
+    foo2(&f1);
+    let f2 = &f1;
+    foo2(f2);
+    let f3: &Fat<[Bar]> = f2;
+    foo2(f3);
+    let f4: &Fat<[Bar]> = &f1;
+    foo2(f4);
+    let f5: &Fat<[Bar]> = &(5, "some str", [bar, bar, bar]);
+    foo2(f5);
+
+    // Assignment.
+    let f5: &mut Fat<[isize]> = &mut (5, "some str", [1, 2, 3]);
+    f5.2[1] = 34;
+    assert_eq!(f5.2[0], 1);
+    assert_eq!(f5.2[1], 34);
+    assert_eq!(f5.2[2], 3);
+
+    // Zero size vec.
+    let f5: &Fat<[isize]> = &(5, "some str", []);
+    assert!(f5.2.is_empty());
+    let f5: &Fat<[Bar]> = &(5, "some str", []);
+    assert!(f5.2.is_empty());
+
+    // Deeply nested.
+    let f1 = (5, "some str", (8, "deep str", [1, 2, 3]));
+    foo3(&f1);
+    let f2 = &f1;
+    foo3(f2);
+    let f3: &Fat<Fat<[isize]>> = f2;
+    foo3(f3);
+    let f4: &Fat<Fat<[isize]>> = &f1;
+    foo3(f4);
+    let f5: &Fat<Fat<[isize]>> = &(5, "some str", (8, "deep str", [1, 2, 3]));
+    foo3(f5);
+
+    // Box.
+    let f1 = Box::new([1, 2, 3]);
+    assert_eq!((*f1)[1], 2);
+    let f2: Box<[isize]> = f1;
+    assert_eq!((*f2)[1], 2);
+
+    // Nested Box.
+    let f1 : Box<Fat<[isize; 3]>> = box (5, "some str", [1, 2, 3]);
+    foo(&*f1);
+    let f2 : Box<Fat<[isize]>> = f1;
+    foo(&*f2);
+
+    let f3 : Box<Fat<[isize]>> =
+        Box::<Fat<[_; 3]>>::new((5, "some str", [1, 2, 3]));
+    foo(&*f3);
+}