Forbid closures that outlive their signature

* This prevents the AST borrow checker from incorrectly accepting
closures that return references to local variables and that are never
called.
* This also ensures that existential types don't end up containing
any `ReScope`s

Author: matthewjasper

src/librustc/ty/outlives.rs

@@ -65,6 +65,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                 for upvar_ty in substs.upvar_tys(def_id, *self) {
                     self.compute_components(upvar_ty, out);
                 }
+                self.compute_components(substs.closure_sig_ty(def_id, *self), out);
             }
 
             ty::Generator(def_id, ref substs, _) => {
@@ -73,6 +74,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     self.compute_components(upvar_ty, out);
                 }
 
+                self.compute_components(substs.return_ty(def_id, *self), out);
+                self.compute_components(substs.yield_ty(def_id, *self), out);
                 // We ignore regions in the generator interior as we don't
                 // want these to affect region inference
             }

src/librustc_metadata/decoder.rs

@@ -135,7 +135,7 @@ impl<'a, 'tcx: 'a, T: Decodable> Lazy<T> {
     }
 }
 
-impl<'a, 'tcx: 'a, T: Decodable> LazySeq<T> {
+impl<'a, 'tcx: 'a, T: Decodable + 'a> LazySeq<T> {
     pub fn decode<M: Metadata<'a, 'tcx>>(
         self,
         meta: M,

src/test/incremental/hashes/closure_expressions.rs

@@ -49,14 +49,14 @@ pub fn add_parameter() {
 // Change parameter pattern ----------------------------------------------------
 #[cfg(cfail1)]
 pub fn change_parameter_pattern() {
-    let _ = |x: &u32| x;
+    let _ = |x: (u32,)| x;
 }
 
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2", except="HirBody, mir_built, typeck_tables_of")]
 #[rustc_clean(cfg="cfail3")]
 pub fn change_parameter_pattern() {
-    let _ = |&x: &u32| x;
+    let _ = |(x,): (u32,)| x;
 }
 
 

src/test/run-pass/regions/regions-relate-bound-regions-on-closures-to-inference-variables.rs

@@ -44,7 +44,7 @@ impl<'a,'tcx> Foo<'a,'tcx> {
 
     fn elaborate_bounds(
         &mut self,
-        mut mk_cand: Box<for<'b> FnMut(&mut Foo<'b, 'tcx>) -> isize>)
+        mut mk_cand: Box<for<'b> FnMut(&mut Foo<'b, 'tcx>) -> isize + 'tcx>)
         -> isize
     {
         mk_cand(self)

src/test/ui/impl-trait/issue-55608-captures-empty-region.rs

@@ -1,9 +1,9 @@
 // This used to ICE because it creates an `impl Trait` that captures a
 // hidden empty region.
 
-#![feature(conservative_impl_trait)]
+// compile-pass
 
-fn server() -> impl FilterBase2 { //~ ERROR [E0700]
+fn server() -> impl FilterBase2 {
     segment2(|| { loop { } }).map2(|| "")
 }
 

src/test/ui/impl-trait/issue-55608-captures-empty-region.stderr

@@ -1,11 +1,10 @@
-// compile-pass
 #![allow(unused)]
 
 fn f() {
     let mut x: Box<()> = Box::new(());
 
     || {
-        &mut x
+        &mut x //~ ERROR cannot infer
     };
 }
 

src/test/ui/issues/issue-40510-1.rs

@@ -1,13 +1,33 @@
-warning: captured variable cannot escape `FnMut` closure body
-  --> $DIR/issue-40510-1.rs:8:9
+error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements
+  --> $DIR/issue-40510-1.rs:7:9
+   |
+LL |         &mut x
+   |         ^^^^^^
+   |
+note: first, the lifetime cannot outlive the lifetime '_ as defined on the body at 6:5...
+  --> $DIR/issue-40510-1.rs:6:5
    |
 LL |     || {
-   |      - inferred to be a `FnMut` closure
+   |     ^^
+note: ...so that closure can access `x`
+  --> $DIR/issue-40510-1.rs:7:9
+   |
 LL |         &mut x
-   |         ^^^^^^ returns a reference to a captured variable which escapes the closure body
+   |         ^^^^^^
+note: but, the lifetime must be valid for the expression at 6:5...
+  --> $DIR/issue-40510-1.rs:6:5
+   |
+LL | /     || {
+LL | |         &mut x
+LL | |     };
+   | |_____^
+note: ...so type `[closure@$DIR/issue-40510-1.rs:6:5: 8:6 x:&mut std::boxed::Box<()>]` of expression is valid during the expression
+  --> $DIR/issue-40510-1.rs:6:5
    |
-   = note: `FnMut` closures only have access to their captured variables while they are executing...
-   = note: ...therefore, they cannot allow references to captured variables to escape
-   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
-   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+LL | /     || {
+LL | |         &mut x
+LL | |     };
+   | |_____^
+
+error: aborting due to previous error
 

src/test/ui/issues/issue-40510-1.stderr

@@ -1,11 +1,10 @@
-// compile-pass
 #![allow(unused)]
 
 fn f() {
     let mut x: Vec<()> = Vec::new();
 
     || {
-        || {
+        || { //~ ERROR captured variable cannot escape `FnMut` closure body
             x.push(())
         }
     };

src/test/ui/issues/issue-40510-3.rs

@@ -1,5 +1,5 @@
-warning: captured variable cannot escape `FnMut` closure body
-  --> $DIR/issue-40510-3.rs:8:9
+error: captured variable cannot escape `FnMut` closure body
+  --> $DIR/issue-40510-3.rs:7:9
    |
 LL |       || {
    |        - inferred to be a `FnMut` closure
@@ -10,6 +10,6 @@ LL | |         }
    |
    = note: `FnMut` closures only have access to their captured variables while they are executing...
    = note: ...therefore, they cannot allow references to captured variables to escape
-   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
-   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
+
+error: aborting due to previous error
 

src/test/ui/issues/issue-40510-3.stderr

@@ -2,10 +2,10 @@
 fn iter<'a>(data: &'a [usize]) -> impl Iterator<Item = usize> + 'a {
     data.iter()
         .map(
-            |x| x // fn(&'a usize) -> &'(ReScope) usize
+            |x| x // fn(&'a usize) -> &'a usize
         )
         .map(
-            |x| *x // fn(&'(ReScope) usize) -> usize
+            |x| *x // fn(&'a usize) -> usize
         )
 }
 

src/test/ui/issues/issue-49556.rs

@@ -1,16 +1,10 @@
-#![feature(rustc_attrs)]
-
 // This test checks that a warning occurs with migrate mode.
 
-#[rustc_error]
 fn main() {
-    //~^ ERROR compilation successful
     let mut x = 0;
     || {
         || {
-        //~^ WARNING captured variable cannot escape `FnMut` closure body
-        //~| WARNING this error has been downgraded to a warning
-        //~| WARNING this warning will become a hard error in the future
+        //~^ ERROR captured variable cannot escape `FnMut` closure body
             let _y = &mut x;
         }
     };

src/test/ui/issues/issue-49824.rs

@@ -1,32 +1,16 @@
-warning: captured variable cannot escape `FnMut` closure body
-  --> $DIR/issue-49824.rs:10:9
+error: captured variable cannot escape `FnMut` closure body
+  --> $DIR/issue-49824.rs:6:9
    |
 LL |       || {
    |        - inferred to be a `FnMut` closure
 LL | /         || {
 LL | |
-LL | |
-LL | |
 LL | |             let _y = &mut x;
 LL | |         }
    | |_________^ returns a closure that contains a reference to a captured variable, which then escapes the closure body
    |
    = note: `FnMut` closures only have access to their captured variables while they are executing...
    = note: ...therefore, they cannot allow references to captured variables to escape
-   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
-   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
-
-error: compilation successful
-  --> $DIR/issue-49824.rs:6:1
-   |
-LL | / fn main() {
-LL | |
-LL | |     let mut x = 0;
-LL | |     || {
-...  |
-LL | |     };
-LL | | }
-   | |_^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-49824.stderr

@@ -12,16 +12,16 @@ LL |     with(|o| o)
    = note: ...so that the expression is assignable:
            expected &isize
               found &isize
-note: but, the lifetime must be valid for the expression at 18:5...
+note: but, the lifetime must be valid for the call at 18:5...
   --> $DIR/regions-escape-via-trait-or-not.rs:18:5
    |
 LL |     with(|o| o)
-   |     ^^^^
-note: ...so type `fn([closure@$DIR/regions-escape-via-trait-or-not.rs:18:10: 18:15]) -> isize {with::<&isize, [closure@$DIR/regions-escape-via-trait-or-not.rs:18:10: 18:15]>}` of expression is valid during the expression
-  --> $DIR/regions-escape-via-trait-or-not.rs:18:5
+   |     ^^^^^^^^^^^
+note: ...so that argument is valid for the call
+  --> $DIR/regions-escape-via-trait-or-not.rs:18:10
    |
 LL |     with(|o| o)
-   |     ^^^^
+   |          ^^^^^
 
 error: aborting due to previous error
 

src/test/ui/regions/regions-escape-via-trait-or-not.stderr

@@ -4,7 +4,7 @@ fn main() {
     // Unboxed closure case
     {
         let mut x = 0;
-        let mut f = || &mut x; //~ ERROR cannot infer
+        let mut f = || &mut x; //~ ERROR borrowed data cannot be stored outside of its closure
         let x = f();
         let y = f();
     }

src/test/ui/regions/regions-return-ref-to-upvar-issue-17403.rs

@@ -1,29 +1,11 @@
-error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements
+error: borrowed data cannot be stored outside of its closure
   --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:24
    |
 LL |         let mut f = || &mut x;
-   |                        ^^^^^^
-   |
-note: first, the lifetime cannot outlive the lifetime '_ as defined on the body at 7:21...
-  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:21
-   |
-LL |         let mut f = || &mut x;
-   |                     ^^^^^^^^^
-note: ...so that closure can access `x`
-  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:24
-   |
-LL |         let mut f = || &mut x;
-   |                        ^^^^^^
-note: but, the lifetime must be valid for the call at 9:17...
-  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:9:17
-   |
-LL |         let y = f();
-   |                 ^^^
-note: ...so type `&mut i32` of expression is valid during the expression
-  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:9:17
-   |
-LL |         let y = f();
-   |                 ^^^
+   |             -----   -- ^^^^^^ cannot be stored outside of its closure
+   |             |       |
+   |             |       ...because it cannot outlive this closure
+   |             borrowed data cannot be stored into here...
 
 error: aborting due to previous error