Unit tests for rust-lang#57464 ICE.

src/test/ui/issues/issue-57464-avoid-eager-conversion-to-region-vid.ast.stderr

@@ -0,0 +1,15 @@
+error[E0373]: closure may outlive the current function, but it borrows `local`, which is owned by the current function
+  --> $DIR/issue-57464-avoid-eager-conversion-to-region-vid.rs:45:13
+   |
+LL |     let m = |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^              ----- `local` is borrowed here
+   |             |
+   |             may outlive borrowed value `local`
+help: to force the closure to take ownership of `local` (and any other referenced variables), use the `move` keyword
+   |
+LL |     let m = move |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0373`.

src/test/ui/issues/issue-57464-avoid-eager-conversion-to-region-vid.mig.stderr

@@ -0,0 +1,14 @@
+error[E0373]: closure may outlive the current function, but it borrows `local`, which is owned by the current function
+  --> $DIR/issue-57464-avoid-eager-conversion-to-region-vid.rs:46:13
+   |
+LL |     let m = |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^              ----- `local` is borrowed here
+   |             |
+   |             may outlive borrowed value `local`
+help: to force the closure to take ownership of `local` (and any other referenced variables), use the `move` keyword
+   |
+LL |     let m = move |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/issues/issue-57464-avoid-eager-conversion-to-region-vid.nll.stderr

@@ -0,0 +1,21 @@
+error[E0373]: closure may outlive the current function, but it borrows `local`, which is owned by the current function
+  --> $DIR/issue-57464-avoid-eager-conversion-to-region-vid.rs:45:13
+   |
+LL |     let m = |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^              ----- `local` is borrowed here
+   |             |
+   |             may outlive borrowed value `local`
+   |
+note: closure is returned here
+  --> $DIR/issue-57464-avoid-eager-conversion-to-region-vid.rs:51:5
+   |
+LL |     and_then(f)
+   |     ^^^^^^^^^^^
+help: to force the closure to take ownership of `local` (and any other referenced variables), use the `move` keyword
+   |
+LL |     let m = move |_: ()| poll_fn(|| { local; });
+   |             ^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0373`.

src/test/ui/issues/issue-57464-avoid-eager-conversion-to-region-vid.rs

@@ -0,0 +1,52 @@
+// This test managed to tickle a part of the compiler where a region
+// representing a static scope (a call-site scope, to be precise) was
+// leaking the where clause of a type underlying an `impl Trait`. This
+// caused an ICE in spots where we assume that all regions must be
+// region_vid's (unique representatives used in NLL) and then
+// attempted to eagerly convert the region to its region_vid, which
+// does not work for scopes which do not have region_vids (apart from
+// the 'static region).
+//
+// This regression test is just meant to check that we do not ICE,
+// regardless of whether NLL is turned on or not.
+
+// revisions: ast nll
+//[ast]compile-flags: -Z borrowck=ast
+//[mig]compile-flags: -Z borrowck=migrate -Z two-phase-borrows
+//[nll]compile-flags: -Z borrowck=mir -Z two-phase-borrows
+
+// don't worry about the --compare-mode=nll on this test.
+// ignore-compare-mode-nll
+
+pub struct AndThen<B, F>(B, F);
+fn and_then<F, B>(_: F) -> AndThen<B, F> where F: FnOnce() -> B { unimplemented!() }
+
+pub trait Trait { }
+impl<B, F> Trait for AndThen<B, F> { }
+
+pub struct JoinAll<I> where I: Iterator { _elem: std::marker::PhantomData<I::Item> }
+pub fn join_all<I>(_i: I) -> JoinAll<I> where I: Iterator { unimplemented!() }
+
+pub struct PollFn<F, T>(F, std::marker::PhantomData<fn () -> T>);
+pub fn poll_fn<T, F>(_f: F) -> PollFn<F, T> where F: FnMut() -> T { unimplemented!() }
+
+impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
+    type Item = B;
+    fn next(&mut self) -> Option<B> { unimplemented!() }
+}
+
+struct Map<I, F> { iter: I, f: F }
+
+fn main() { let _b: Box<Trait + Send> = Box::new(graphql()); }
+
+fn graphql() -> impl Trait
+{
+    let local = ();
+    let m = |_: ()| poll_fn(|| { local; });
+    //[ast]~^   ERROR closure may outlive the current function, but it borrows `local`
+    //[mig]~^^  ERROR closure may outlive the current function, but it borrows `local`
+    //[nll]~^^^ ERROR closure may outlive the current function, but it borrows `local`
+    let v = Map { iter: std::iter::once(()), f: m };
+    let f = || join_all(v);
+    and_then(f)
+}