Add regresion test for rust-lang#87142

Author: JohnTitor

src/test/ui/generator/issue-87142.rs

@@ -0,0 +1,32 @@
+// compile-flags: -Cdebuginfo=2
+// build-pass
+
+// Regression test for #87142
+// This test needs the above flags and the "lib" crate type.
+
+#![feature(type_alias_impl_trait, generator_trait, generators)]
+#![crate_type = "lib"]
+
+use std::ops::Generator;
+
+pub trait GeneratorProviderAlt: Sized {
+    type Gen: Generator<(), Return = (), Yield = ()>;
+
+    fn start(ctx: Context<Self>) -> Self::Gen;
+}
+
+pub struct Context<G: 'static + GeneratorProviderAlt> {
+    pub link: Box<G::Gen>,
+}
+
+impl GeneratorProviderAlt for () {
+    type Gen = impl Generator<(), Return = (), Yield = ()>;
+    fn start(ctx: Context<Self>) -> Self::Gen {
+        move || {
+            match ctx {
+                _ => (),
+            }
+            yield ();
+        }
+    }
+}