Collect late-bound regions from all closure parents in closure_mapping

src/test/ui/closures/binder/nested-closures-regions.rs

@@ -0,0 +1,9 @@
+// check-pass
+
+#![feature(closure_lifetime_binder)]
+#![feature(rustc_attrs)]
+
+#[rustc_regions]
+fn main() {
+    for<'a> || -> () { for<'c> |_: &'a ()| -> () {}; };
+}

src/test/ui/closures/binder/nested-closures-regions.stderr

@@ -0,0 +1,38 @@
+note: external requirements
+  --> $DIR/nested-closures-regions.rs:8:24
+   |
+LL |     for<'a> || -> () { for<'c> |_: &'a ()| -> () {}; };
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: defining type: main::{closure#0}::{closure#0} with closure substs [
+               i8,
+               extern "rust-call" fn((&(),)),
+               (),
+           ]
+   = note: late-bound region is '_#4r
+   = note: late-bound region is '_#2r
+   = note: number of external vids: 3
+   = note: where '_#1r: '_#2r
+   = note: where '_#2r: '_#1r
+
+note: no external requirements
+  --> $DIR/nested-closures-regions.rs:8:5
+   |
+LL |     for<'a> || -> () { for<'c> |_: &'a ()| -> () {}; };
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = note: defining type: main::{closure#0} with closure substs [
+               i8,
+               extern "rust-call" fn(()),
+               (),
+           ]
+   = note: late-bound region is '_#2r
+
+note: no external requirements
+  --> $DIR/nested-closures-regions.rs:7:1
+   |
+LL | fn main() {
+   | ^^^^^^^^^
+   |
+   = note: defining type: main
+