Auto merge of #27215 - pnkfelix:fsk-placer-take-5-just-in, r=nikomatsakis

Macro desugaring of `in PLACE { BLOCK }` into "simpler" expressions following the in-development "Placer" protocol.

Includes Placer API that one can override to integrate support for `in` into one's own type.  (See [RFC 809].)

[RFC 809]: https://github.com/rust-lang/rfcs/blob/master/text/0809-box-and-in-for-stdlib.md

Part of #22181

Replaced PR #26180.

Turns on the `in PLACE { BLOCK }` syntax, while leaving in support for the old `box (PLACE) EXPR` syntax (since we need to support that at least until we have a snapshot with support for `in PLACE { BLOCK }`.

(Note that we are not 100% committed to the `in PLACE { BLOCK }` syntax.  In particular I still want to play around with some other alternatives.  Still, I want to get the fundamental framework for the protocol landed so we can play with implementing it for non `Box` types.)

----

Also, this PR leaves out support for desugaring-based `box EXPR`.  We will hopefully land that in the future, but for the short term there are type-inference issues injected by that change that we want to resolve separately.

src/test/compile-fail/feature-gate-box-expr.rs

@@ -8,15 +8,18 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn main() {
-    use std::boxed::HEAP;
+// Check that `box EXPR` is feature-gated.
+//
+// See also feature-gate-placement-expr.rs
+//
+// (Note that the two tests are separated since the checks appear to
+// be performed at distinct phases, with an abort_if_errors call
+// separating them.)
 
+fn main() {
     let x = box 'c'; //~ ERROR box expression syntax is experimental
     println!("x: {}", x);
 
     let x = box () 'c'; //~ ERROR box expression syntax is experimental
     println!("x: {}", x);
-
-    let x = box (HEAP) 'c'; //~ ERROR box expression syntax is experimental
-    println!("x: {}", x);
 }

src/test/compile-fail/feature-gate-placement-expr.rs

@@ -0,0 +1,27 @@
+// Copyright 2015 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.
+
+// Check that `in PLACE { EXPR }` is feature-gated.
+//
+// See also feature-gate-box-expr.rs
+//
+// (Note that the two tests are separated since the checks appear to
+// be performed at distinct phases, with an abort_if_errors call
+// separating them.)
+
+fn main() {
+    use std::boxed::HEAP;
+
+    let x = box (HEAP) 'c'; //~ ERROR placement-in expression syntax is experimental
+    println!("x: {}", x);
+
+    let x = in HEAP { 'c' }; //~ ERROR placement-in expression syntax is experimental
+    println!("x: {}", x);
+}

src/test/compile-fail/feature-gate-pushpop-unsafe.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 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 c = push_unsafe!('c'); //~ ERROR push/pop_unsafe macros are experimental
+    let c = pop_unsafe!('c'); //~ ERROR push/pop_unsafe macros are experimental
+}

src/test/compile-fail/issue-14084.rs

@@ -9,8 +9,10 @@
 // except according to those terms.
 
 #![feature(box_syntax)]
+#![feature(placement_in_syntax)]
 
 fn main() {
     box ( () ) 0;
-    //~^ ERROR: only the exchange heap is currently supported
+    //~^ ERROR: the trait `core::ops::Placer<_>` is not implemented
+    //~| ERROR: the trait `core::ops::Placer<_>` is not implemented
 }

src/test/compile-fail/pushpop-unsafe-rejects.rs

@@ -0,0 +1,74 @@
+// Copyright 2012 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.
+
+// Basic sanity check for `push_unsafe!(EXPR)` and
+// `pop_unsafe!(EXPR)`: we can call unsafe code when there are a
+// positive number of pushes in the stack, or if we are within a
+// normal `unsafe` block, but otherwise cannot.
+
+#![feature(pushpop_unsafe)]
+
+static mut X: i32 = 0;
+
+unsafe fn f() { X += 1; return; }
+fn g() { unsafe { X += 1_000; } return; }
+
+fn main() {
+    push_unsafe!( {
+        f(); pop_unsafe!({
+            f() //~ ERROR: call to unsafe function
+        })
+    } );
+
+    push_unsafe!({
+        f();
+        pop_unsafe!({
+            g();
+            f(); //~ ERROR: call to unsafe function
+        })
+    } );
+
+    push_unsafe!({
+        g(); pop_unsafe!({
+            unsafe {
+                f();
+            }
+            f(); //~ ERROR: call to unsafe function
+        })
+    });
+
+
+    // Note: For implementation simplicity the compiler just
+    // ICE's if you underflow the push_unsafe stack.
+    //
+    // Thus all of the following cases cause an ICE.
+    //
+    // (The "ERROR" notes are from an earlier version
+    //  that used saturated arithmetic rather than checked
+    //  arithmetic.)
+
+    //    pop_unsafe!{ g() };
+    //
+    //    push_unsafe!({
+    //        pop_unsafe!(pop_unsafe!{ g() })
+    //    });
+    //
+    //    push_unsafe!({
+    //        g();
+    //        pop_unsafe!(pop_unsafe!({
+    //            f() // ERROR: call to unsafe function
+    //        }))
+    //    });
+    //
+    //    pop_unsafe!({
+    //        f(); // ERROR: call to unsafe function
+    //    })
+
+}

src/test/parse-fail/parenthesized-box-expr-message.rs

@@ -12,7 +12,7 @@
 
 fn main() {
     box (1 + 1)
-    //~^ HELP try using `box()` instead:
-    //~| SUGGESTION box() (1 + 1)
+    //~^ HELP try using `box ()` instead:
+    //~| SUGGESTION box () (1 + 1)
     ; //~ ERROR expected expression, found `;`
 }

src/test/run-pass/intrinsic-move-val.rs

@@ -20,7 +20,7 @@ use std::mem::{self, transmute};
 mod rusti {
     extern "rust-intrinsic" {
         pub fn init<T>() -> T;
-        pub fn move_val_init<T>(dst: &mut T, src: T);
+        pub fn move_val_init<T>(dst: *mut T, src: T);
     }
 }
 

src/test/run-pass/new-box-syntax.rs

@@ -13,8 +13,13 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
-#![allow(warnings)]
+#![allow(dead_code, unused_variables)]
 #![feature(box_syntax, box_heap)]
+#![feature(placement_in_syntax)]
+
+// during check-pretty, the expanded code needs to opt into these
+// features
+#![feature(placement_new_protocol, core_intrinsics)]
 
 // Tests that the new `box` syntax works with unique pointers.
 
@@ -30,4 +35,9 @@ pub fn main() {
     let y: Box<isize> = box 2;
     let b: Box<isize> = box()(1 + 2);
     let c = box()(3 + 4);
+
+    let s: Box<Structure> = box Structure {
+        x: 3,
+        y: 4,
+    };
 }

src/test/run-pass/placement-in-syntax.rs

@@ -0,0 +1,37 @@
+// Copyright 2015 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(dead_code, unused_variables)]
+#![feature(box_heap)]
+#![feature(placement_in_syntax)]
+
+// Tests that the new `in` syntax works with unique pointers.
+//
+// Compare with new-box-syntax.rs
+
+use std::boxed::{Box, HEAP};
+
+struct Structure {
+    x: isize,
+    y: isize,
+}
+
+pub fn main() {
+    let x: Box<isize> = in HEAP { 2 };
+    let b: Box<isize> = in HEAP { 1 + 2 };
+    let c = in HEAP { 3 + 4 };
+
+    let s: Box<Structure> = in HEAP {
+        Structure {
+            x: 3,
+            y: 4,
+        }
+    };
+}

src/test/run-pass/pushpop-unsafe-okay.rs

@@ -0,0 +1,56 @@
+// Copyright 2015 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.
+
+// Basic sanity check for `push_unsafe!(EXPR)` and
+// `pop_unsafe!(EXPR)`: we can call unsafe code when there are a
+// positive number of pushes in the stack, or if we are within a
+// normal `unsafe` block, but otherwise cannot.
+
+// ignore-pretty because the `push_unsafe!` and `pop_unsafe!` macros
+// are not integrated with the pretty-printer.
+
+#![feature(pushpop_unsafe)]
+
+static mut X: i32 = 0;
+
+unsafe fn f() { X += 1; return; }
+fn g() { unsafe { X += 1_000; } return; }
+
+fn check_reset_x(x: i32) -> bool {
+    #![allow(unused_parens)] // dont you judge my style choices!
+    unsafe {
+        let ret = (x == X);
+        X = 0;
+        ret
+    }
+}
+
+fn main() {
+    // double-check test infrastructure
+    assert!(check_reset_x(0));
+    unsafe { f(); }
+    assert!(check_reset_x(1));
+    assert!(check_reset_x(0));
+    { g(); }
+    assert!(check_reset_x(1000));
+    assert!(check_reset_x(0));
+    unsafe { f(); g(); g(); }
+    assert!(check_reset_x(2001));
+
+    push_unsafe!( { f(); pop_unsafe!( g() ) } );
+    assert!(check_reset_x(1_001));
+    push_unsafe!( { g(); pop_unsafe!( unsafe { f(); f(); } ) } );
+    assert!(check_reset_x(1_002));
+
+    unsafe { push_unsafe!( { f(); pop_unsafe!( { f(); f(); } ) } ); }
+    assert!(check_reset_x(3));
+    push_unsafe!( { f(); push_unsafe!( { pop_unsafe!( { f(); f(); f(); } ) } ); } );
+    assert!(check_reset_x(4));
+}