Label closure captures/generator locals that make opaque types recursive

3 files changed, 46 insertions, 0 deletions

diff --git a/tests/ui/impl-trait/recursive-generator.rs b/tests/ui/impl-trait/recursive-generator.rs
new file mode 100644
index 00000000000..e876f0fb43f
--- /dev/null
+++ b/tests/ui/impl-trait/recursive-generator.rs
@@ -0,0 +1,23 @@
+#![feature(generators, generator_trait)]
+
+use std::ops::{Generator, GeneratorState};
+
+fn foo() -> impl Generator<Yield = (), Return = ()> {
+    //~^ ERROR cannot resolve opaque type
+    //~| NOTE recursive opaque type
+    //~| NOTE in this expansion of desugaring of
+    || {
+    //~^ NOTE returning here
+        let mut gen = Box::pin(foo());
+        //~^ NOTE generator captures itself here
+        let mut r = gen.as_mut().resume(());
+        while let GeneratorState::Yielded(v) = r {
+            yield v;
+            r = gen.as_mut().resume(());
+        }
+    }
+}
+
+fn main() {
+    foo();
+}
diff --git a/tests/ui/impl-trait/recursive-generator.stderr b/tests/ui/impl-trait/recursive-generator.stderr
new file mode 100644
index 00000000000..e23fd4b4a85
--- /dev/null
+++ b/tests/ui/impl-trait/recursive-generator.stderr
@@ -0,0 +1,19 @@
+error[E0720]: cannot resolve opaque type
+  --> $DIR/recursive-generator.rs:5:13
+   |
+LL |   fn foo() -> impl Generator<Yield = (), Return = ()> {
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ recursive opaque type
+...
+LL | /     || {
+LL | |
+LL | |         let mut gen = Box::pin(foo());
+   | |             ------- generator captures itself here
+LL | |
+...  |
+LL | |         }
+LL | |     }
+   | |_____- returning here with type `[generator@$DIR/recursive-generator.rs:9:5: 9:7]`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0720`.
diff --git a/tests/ui/impl-trait/recursive-impl-trait-type-indirect.stderr b/tests/ui/impl-trait/recursive-impl-trait-type-indirect.stderr
index 2e34d3d4275..ebb231ae14f 100644
--- a/tests/ui/impl-trait/recursive-impl-trait-type-indirect.stderr
+++ b/tests/ui/impl-trait/recursive-impl-trait-type-indirect.stderr
@@ -53,6 +53,7 @@ LL |   fn closure_capture() -> impl Sized {
 ...
 LL | /     move || {
 LL | |         x;
+   | |         - closure captures itself here
 LL | |     }
    | |_____- returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:35:5: 35:12]`
 
@@ -64,6 +65,7 @@ LL |   fn closure_ref_capture() -> impl Sized {
 ...
 LL | /     move || {
 LL | |         &x;
+   | |          - closure captures itself here
 LL | |     }
    | |_____- returning here with type `[closure@$DIR/recursive-impl-trait-type-indirect.rs:43:5: 43:12]`
 
@@ -94,6 +96,7 @@ LL |   fn generator_capture() -> impl Sized {
 LL | /     move || {
 LL | |         yield;
 LL | |         x;
+   | |         - generator captures itself here
 LL | |     }
    | |_____- returning here with type `[generator@$DIR/recursive-impl-trait-type-indirect.rs:61:5: 61:12]`
 
@@ -114,6 +117,7 @@ LL |   fn generator_hold() -> impl Sized {
 LL |
 LL | /     move || {
 LL | |         let x = generator_hold();
+   | |             - generator captures itself here
 LL | |         yield;
 LL | |         x;
 LL | |     }