project: add a recursion limit to "tail-recursive" projections

Fixes #21946
Fixes #23992
Fixes #25945

src/librustc/middle/traits/project.rs

@@ -343,7 +343,8 @@ pub fn normalize_projection_type<'a,'b,'tcx>(
                 projection_ty: projection_ty,
                 ty: ty_var
             });
-            let obligation = Obligation::with_depth(cause, depth+1, projection.to_predicate());
+            let obligation = Obligation::with_depth(
+                cause, depth + 1, projection.to_predicate());
             Normalized {
                 value: ty_var,
                 obligations: vec!(obligation)
@@ -382,7 +383,7 @@ fn opt_normalize_projection_type<'a,'b,'tcx>(
                    obligations);
 
             if projected_ty.has_projection_types() {
-                let mut normalizer = AssociatedTypeNormalizer::new(selcx, cause, depth);
+                let mut normalizer = AssociatedTypeNormalizer::new(selcx, cause, depth+1);
                 let normalized_ty = normalizer.fold(&projected_ty);
 
                 debug!("normalize_projection_type: normalized_ty={:?} depth={}",

src/test/compile-fail/issue-21946.rs

@@ -0,0 +1,22 @@
+// Copyright 2015 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.
+
+trait Foo {
+    type A;
+}
+
+struct FooStruct;
+
+impl Foo for FooStruct {
+//~^ ERROR overflow evaluating the requirement `<FooStruct as Foo>::A`
+    type A = <FooStruct as Foo>::A;
+}
+
+fn main() {}

src/test/run-pass/issue-23992.rs

@@ -0,0 +1,28 @@
+// Copyright 2015 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.
+
+pub struct Outer<T: Trait>(T);
+pub struct Inner<'a> { value: &'a bool }
+
+pub trait Trait {
+    type Error;
+    fn ready(self) -> Self::Error;
+}
+
+impl<'a> Trait for Inner<'a> {
+    type Error = Outer<Inner<'a>>;
+    fn ready(self) -> Outer<Inner<'a>> { Outer(self) }
+}
+
+fn main() {
+    let value = true;
+    let inner = Inner { value: &value };
+    assert_eq!(inner.ready().0.value, &value);
+}