From 837856d120ec3350f1e9d194801a6a89e5d71630 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Mon, 11 Mar 2019 16:30:40 +0100
Subject: [PATCH] Test illustrating that the nested_impl_trait lint should only
 catch shallow cases.

---
 ...-deeply-nested-impl-trait-in-assoc-proj.rs | 42 +++++++++++++++++++
 ...ply-nested-impl-trait-in-assoc-proj.stderr | 30 +++++++++++++
 2 files changed, 72 insertions(+)
 create mode 100644 src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs
 create mode 100644 src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.stderr

diff --git a/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs b/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs
new file mode 100644
index 00000000000..5eef6a39325
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs
@@ -0,0 +1,42 @@
+// rust-lang/rust#57979 : the initial support for `impl Trait` didn't
+// properly check syntax hidden behind an associated type projection,
+// but it did catch *some cases*. This is checking that we continue to
+// properly emit errors for those, even with the new
+// future-incompatibility warnings.
+//
+// issue-57979-nested-impl-trait-in-assoc-proj.rs shows the main case
+// that we were previously failing to catch.
+
+struct Deeper<T>(T);
+
+mod allowed {
+    #![allow(nested_impl_trait)]
+
+    pub trait Foo<T> { }
+    pub trait Bar { }
+    pub trait Quux { type Assoc; }
+    pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+    //~^ ERROR nested `impl Trait` is not allowed
+}
+
+mod warned {
+    #![warn(nested_impl_trait)]
+
+    pub trait Foo<T> { }
+    pub trait Bar { }
+    pub trait Quux { type Assoc; }
+    pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+    //~^ ERROR nested `impl Trait` is not allowed
+}
+
+mod denied {
+    #![deny(nested_impl_trait)]
+
+    pub trait Foo<T> { }
+    pub trait Bar { }
+    pub trait Quux { type Assoc; }
+    pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+    //~^ ERROR nested `impl Trait` is not allowed
+}
+
+fn main() { }
diff --git a/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.stderr b/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.stderr
new file mode 100644
index 00000000000..2b6f15e6d3e
--- /dev/null
+++ b/src/test/ui/impl-trait/issue-57979-deeply-nested-impl-trait-in-assoc-proj.stderr
@@ -0,0 +1,30 @@
+error[E0666]: nested `impl Trait` is not allowed
+  --> $DIR/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs:18:59
+   |
+LL |     pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+   |                                                  ---------^^^^^^^^-
+   |                                                  |        |
+   |                                                  |        nested `impl Trait` here
+   |                                                  outer `impl Trait`
+
+error[E0666]: nested `impl Trait` is not allowed
+  --> $DIR/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs:28:59
+   |
+LL |     pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+   |                                                  ---------^^^^^^^^-
+   |                                                  |        |
+   |                                                  |        nested `impl Trait` here
+   |                                                  outer `impl Trait`
+
+error[E0666]: nested `impl Trait` is not allowed
+  --> $DIR/issue-57979-deeply-nested-impl-trait-in-assoc-proj.rs:38:59
+   |
+LL |     pub fn demo(_: impl Quux<Assoc=super::Deeper<impl Foo<impl Bar>>>) { }
+   |                                                  ---------^^^^^^^^-
+   |                                                  |        |
+   |                                                  |        nested `impl Trait` here
+   |                                                  outer `impl Trait`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0666`.
-- 
2.44.0