Optimized error reporting for recursive requirements #47720

src/test/ui/recursive-requirements.rs

@@ -0,0 +1,27 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::marker::PhantomData;
+
+struct AssertSync<T: Sync>(PhantomData<T>);
+
+pub struct Foo {
+    bar: *const Bar,
+    phantom: PhantomData<Bar>,
+}
+
+pub struct Bar {
+    foo: *const Foo,
+    phantom: PhantomData<Foo>,
+}
+
+fn main() {
+    let _: AssertSync<Foo> = unimplemented!(); //~ ERROR E0275
+}

src/test/ui/recursive-requirements.stderr

@@ -0,0 +1,14 @@
+error[E0275]: overflow evaluating the requirement `Foo: std::marker::Sync`
+  --> $DIR/recursive-requirements.rs:26:12
+   |
+26 |     let _: AssertSync<Foo> = unimplemented!(); //~ ERROR E0275
+   |            ^^^^^^^^^^^^^^^
+   |
+   = help: consider adding a `#![recursion_limit="128"]` attribute to your crate
+   = note: required because it appears within the type `std::marker::PhantomData<Foo>`
+   = note: required because it appears within the type `Bar`
+   = note: required because it appears within the type `std::marker::PhantomData<Bar>`
+   = note: required because it appears within the type `Foo`
+
+error: aborting due to previous error
+