add comments and tests

src/test/compile-fail/issue-17431-2.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 struct Baz { q: Option<Foo> }
+//~^ ERROR recursive type `Baz` has infinite size
 
 struct Foo { q: Option<Baz> }
 //~^ ERROR recursive type `Foo` has infinite size

src/test/compile-fail/issue-26548.rs

@@ -8,10 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// error-pattern: overflow representing the type `S`
+
 trait Mirror { type It: ?Sized; }
 impl<T: ?Sized> Mirror for T { type It = Self; }
 struct S(Option<<S as Mirror>::It>);
-//~^ ERROR recursive type `S` has infinite size
 
 fn main() {
     let _s = S(None);

src/test/compile-fail/range-1.rs

@@ -23,5 +23,4 @@ pub fn main() {
     let arr: &[_] = &[1, 2, 3];
     let range = *arr..;
     //~^ ERROR `[_]: std::marker::Sized` is not satisfied
-    //~| ERROR `[_]: std::marker::Sized` is not satisfied
 }

src/test/compile-fail/sized-cycle-note.rs

@@ -17,14 +17,9 @@
 // 2. it should elaborate the steps that led to the cycle.
 
 struct Baz { q: Option<Foo> }
-
+//~^ ERROR recursive type `Baz` has infinite size
 struct Foo { q: Option<Baz> }
 //~^ ERROR recursive type `Foo` has infinite size
-//~| NOTE type `Foo` is embedded within `std::option::Option<Foo>`...
-//~| NOTE ...which in turn is embedded within `std::option::Option<Foo>`...
-//~| NOTE ...which in turn is embedded within `Baz`...
-//~| NOTE ...which in turn is embedded within `std::option::Option<Baz>`...
-//~| NOTE ...which in turn is embedded within `Foo`, completing the cycle.
 
 impl Foo { fn bar(&self) {} }
 

src/test/run-pass/issue-31299.rs

@@ -0,0 +1,36 @@
+// Copyright 2012 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.
+
+// Regression test for #31299. This was generating an overflow error
+// because of eager normalization:
+//
+// proving `M: Sized` requires
+// - proving `PtrBack<Vec<M>>: Sized` requis
+//   - normalizing `Vec<<Vec<M> as Front>::Back>>: Sized` requires
+//     - proving `Vec<M>: Front` requires
+//       - `M: Sized` <-- cycle!
+//
+// If we skip the normalization step, though, everything goes fine.
+
+trait Front {
+    type Back;
+}
+
+impl<T> Front for Vec<T> {
+    type Back = Vec<T>;
+}
+
+struct PtrBack<T: Front>(Vec<T::Back>);
+
+struct M(PtrBack<Vec<M>>);
+
+fn main() {
+    std::mem::size_of::<M>();
+}