Auto merge of #49822 - matthewjasper:dropck-closures, r=nikomatsakis

Access individual fields of tuples, closures and generators on drop.

Fixes #48623, by extending the change in #47917 to closures. Also does this for tuples and generators for consistency.

Enums are unchanged because there is now way to borrow `*enum.field` without borrowing `enum.field` at the moment, so any error would be reported when the enum goes out of scope. Unions aren't changed because unions they don't automatically drop their fields.

r? @nikomatsakis

src/librustc_mir/borrow_check/mod.rs

@@ -20,7 +20,7 @@ use rustc::ty::maps::Providers;
 use rustc::mir::{AssertMessage, BasicBlock, BorrowKind, Location, Place};
 use rustc::mir::{Mir, Mutability, Operand, Projection, ProjectionElem, Rvalue};
 use rustc::mir::{Field, Statement, StatementKind, Terminator, TerminatorKind};
-use rustc::mir::ClosureRegionRequirements;
+use rustc::mir::{ClosureRegionRequirements, Local};
 
 use rustc_data_structures::control_flow_graph::dominators::Dominators;
 use rustc_data_structures::fx::FxHashSet;
@@ -729,6 +729,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         erased_drop_place_ty: ty::Ty<'gcx>,
         span: Span,
     ) {
+        let gcx = self.tcx.global_tcx();
+        let drop_field = |
+            mir: &mut MirBorrowckCtxt<'cx, 'gcx, 'tcx>,
+            (index, field): (usize, ty::Ty<'gcx>),
+        | {
+            let field_ty = gcx.normalize_erasing_regions(mir.param_env, field);
+            let place = drop_place.clone().field(Field::new(index), field_ty);
+
+            mir.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
+        };
+
         match erased_drop_place_ty.sty {
             // When a struct is being dropped, we need to check
             // whether it has a destructor, if it does, then we can
@@ -737,22 +748,31 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             // destructor but `bar` does not, we will only check for
             // borrows of `x.foo` and not `x.bar`. See #47703.
             ty::TyAdt(def, substs) if def.is_struct() && !def.has_dtor(self.tcx) => {
-                for (index, field) in def.all_fields().enumerate() {
-                    let gcx = self.tcx.global_tcx();
-                    let field_ty = field.ty(gcx, substs);
-                    let field_ty = gcx.normalize_erasing_regions(self.param_env, field_ty);
-                    let place = drop_place.clone().field(Field::new(index), field_ty);
-
-                    self.visit_terminator_drop(loc, term, flow_state, &place, field_ty, span);
-                }
+                def.all_fields()
+                    .map(|field| field.ty(gcx, substs))
+                    .enumerate()
+                    .for_each(|field| drop_field(self, field));
+            }
+            // Same as above, but for tuples.
+            ty::TyTuple(tys) => {
+                tys.iter().cloned().enumerate()
+                    .for_each(|field| drop_field(self, field));
+            }
+            // Closures and generators also have disjoint fields, but they are only
+            // directly accessed in the body of the closure/generator.
+            ty::TyClosure(def, substs)
+            | ty::TyGenerator(def, substs, ..)
+                if *drop_place == Place::Local(Local::new(1)) && !self.mir.upvar_decls.is_empty()
+            => {
+                substs.upvar_tys(def, self.tcx).enumerate()
+                    .for_each(|field| drop_field(self, field));
             }
             _ => {
                 // We have now refined the type of the value being
                 // dropped (potentially) to just the type of a
                 // subfield; so check whether that field's type still
                 // "needs drop". If so, we assume that the destructor
                 // may access any data it likes (i.e., a Deep Write).
-                let gcx = self.tcx.global_tcx();
                 if erased_drop_place_ty.needs_drop(gcx, self.param_env) {
                     self.access_place(
                         ContextKind::Drop.new(loc),

src/test/run-pass/issue-47703-tuple.rs

@@ -0,0 +1,21 @@
+// 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.
+
+#![feature(nll)]
+
+struct WithDrop;
+
+impl Drop for WithDrop {
+    fn drop(&mut self) {}
+}
+
+fn consume(x: (&mut (), WithDrop)) -> &mut () { x.0 }
+
+fn main() {}

src/test/run-pass/nll/issue-48623-closure.rs

@@ -0,0 +1,24 @@
+// 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.
+
+#![feature(nll)]
+
+struct WithDrop;
+
+impl Drop for WithDrop {
+    fn drop(&mut self) {}
+}
+
+fn reborrow_from_closure(r: &mut ()) -> &mut () {
+    let d = WithDrop;
+    (move || { d; &mut *r })()
+}
+
+fn main() {}

src/test/run-pass/nll/issue-48623-generator.rs

@@ -0,0 +1,25 @@
+// 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.
+
+#![feature(nll)]
+#![feature(generators, generator_trait)]
+
+struct WithDrop;
+
+impl Drop for WithDrop {
+    fn drop(&mut self) {}
+}
+
+fn reborrow_from_generator(r: &mut ()) {
+    let d = WithDrop;
+    move || { d; yield; &mut *r };
+}
+
+fn main() {}

src/test/ui/generator/yield-while-iterating.nll.stderr

@@ -6,20 +6,6 @@ LL |         for p in &x { //~ ERROR
 LL |             yield();
    |             ------- possible yield occurs here
 
-error[E0597]: borrowed value does not live long enough
-  --> $DIR/yield-while-iterating.rs:50:17
-   |
-LL |       let mut b = || {
-   |  _________________^
-LL | |         for p in &mut x {
-LL | |             yield p;
-LL | |         }
-LL | |     };
-   | |     ^
-   | |     |
-   | |_____temporary value only lives until here
-   |       temporary value does not live long enough
-
 error[E0502]: cannot borrow `x` as immutable because it is also borrowed as mutable
   --> $DIR/yield-while-iterating.rs:67:20
    |
@@ -35,21 +21,7 @@ LL |       println!("{}", x[0]); //~ ERROR
 LL |       b.resume();
    |       - borrow later used here
 
-error[E0597]: borrowed value does not live long enough
-  --> $DIR/yield-while-iterating.rs:62:17
-   |
-LL |       let mut b = || {
-   |  _________________^
-LL | |         for p in &mut x {
-LL | |             yield p;
-LL | |         }
-LL | |     };
-   | |     ^
-   | |     |
-   | |_____temporary value only lives until here
-   |       temporary value does not live long enough
-
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
-Some errors occurred: E0502, E0597, E0626.
+Some errors occurred: E0502, E0626.
 For more information about an error, try `rustc --explain E0502`.