Auto merge of #45879 - nikomatsakis:nll-kill-cyclic-closures, r=arielb1

move closure kind, signature into `ClosureSubsts`

Instead of using side-tables, store the closure-kind and signature in the substitutions themselves. This has two key effects:

- It means that the closure's type changes as inference finds out more things, which is very nice.
    - As a result, it avoids the need for the `freshen_closure_like` code (though we still use it for generators).
- It avoids cyclic closures calls.
    - These were never meant to be supported, precisely because they make a lot of the fancy inference that we do much more complicated. However, due to an oversight, it was previously possible -- if challenging -- to create a setup where a closure *directly* called itself (see e.g. #21410).

We have to see what the effect of this change is, though. Needs a crater run. Marking as [WIP] until that has been assessed.

r? @arielb1

6 files changed, 66 insertions, 7 deletions

diff --git a/src/test/compile-fail/closure-bounds-static-cant-capture-borrowed.rs b/src/test/compile-fail/closure-bounds-static-cant-capture-borrowed.rs
index 16ed73e9095..513a17e2ef2 100644
--- a/src/test/compile-fail/closure-bounds-static-cant-capture-borrowed.rs
+++ b/src/test/compile-fail/closure-bounds-static-cant-capture-borrowed.rs
@@ -13,8 +13,7 @@ fn bar<F>(blk: F) where F: FnOnce() + 'static {
 
 fn foo(x: &()) {
     bar(|| {
-        //~^ ERROR cannot infer
-        //~| ERROR does not fulfill
+        //~^ ERROR does not fulfill
         let _ = x;
     })
 }
diff --git a/src/test/compile-fail/generator-yielding-or-returning-itself.rs b/src/test/compile-fail/generator-yielding-or-returning-itself.rs
new file mode 100644
index 00000000000..13abdf616b2
--- /dev/null
+++ b/src/test/compile-fail/generator-yielding-or-returning-itself.rs
@@ -0,0 +1,45 @@
+// Copyright 2016 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(generator_trait)]
+#![feature(generators)]
+
+// Test that we cannot create a generator that returns a value of its
+// own type.
+
+use std::ops::Generator;
+
+pub fn want_cyclic_generator_return<T>(_: T)
+    where T: Generator<Yield = (), Return = T>
+{
+}
+
+fn supply_cyclic_generator_return() {
+    want_cyclic_generator_return(|| {
+        //~^ ERROR type mismatch
+        if false { yield None.unwrap(); }
+        None.unwrap()
+    })
+}
+
+pub fn want_cyclic_generator_yield<T>(_: T)
+    where T: Generator<Yield = T, Return = ()>
+{
+}
+
+fn supply_cyclic_generator_yield() {
+    want_cyclic_generator_yield(|| {
+        //~^ ERROR type mismatch
+        if false { yield None.unwrap(); }
+        None.unwrap()
+    })
+}
+
+fn main() { }
diff --git a/src/test/compile-fail/issue-22638.rs b/src/test/compile-fail/issue-22638.rs
index 53b0d9f4e9f..1c534ebbd43 100644
--- a/src/test/compile-fail/issue-22638.rs
+++ b/src/test/compile-fail/issue-22638.rs
@@ -19,7 +19,6 @@ struct A (B);
 
 impl A {
     pub fn matches<F: Fn()>(&self, f: &F) {
-        //~^ ERROR reached the recursion limit while instantiating `A::matches::<[closure
         let &A(ref term) = self;
         term.matches(f);
     }
@@ -59,6 +58,7 @@ struct D (Box<A>);
 
 impl D {
     pub fn matches<F: Fn()>(&self, f: &F) {
+        //~^ ERROR reached the type-length limit while instantiating `D::matches::<[closure
         let &D(ref a) = self;
         a.matches(f)
     }
diff --git a/src/test/compile-fail/issue-25439.rs b/src/test/compile-fail/issue-25439.rs
new file mode 100644
index 00000000000..6e33fd5ae71
--- /dev/null
+++ b/src/test/compile-fail/issue-25439.rs
@@ -0,0 +1,19 @@
+// 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.
+
+struct Helper<'a, F: 'a>(&'a F);
+
+fn fix<F>(f: F) -> i32 where F: Fn(Helper<F>, i32) -> i32 {
+    f(Helper(&f), 8)
+}
+
+fn main() {
+    fix(|_, x| x); //~ ERROR closure/generator type that references itself [E0644]
+}
diff --git a/src/test/compile-fail/occurs-check-2.rs b/src/test/compile-fail/occurs-check-2.rs
index a276af83dee..5d162fe944e 100644
--- a/src/test/compile-fail/occurs-check-2.rs
+++ b/src/test/compile-fail/occurs-check-2.rs
@@ -16,7 +16,5 @@ fn main() {
     g = f;
     f = box g;
     //~^  ERROR mismatched types
-    //~| expected type `_`
-    //~| found type `std::boxed::Box<_>`
     //~| cyclic type of infinite size
 }
diff --git a/src/test/compile-fail/occurs-check.rs b/src/test/compile-fail/occurs-check.rs
index 5b6a11e58c2..2c784365ea9 100644
--- a/src/test/compile-fail/occurs-check.rs
+++ b/src/test/compile-fail/occurs-check.rs
@@ -14,7 +14,5 @@ fn main() {
     let f;
     f = box f;
     //~^ ERROR mismatched types
-    //~| expected type `_`
-    //~| found type `std::boxed::Box<_>`
     //~| cyclic type of infinite size
 }