Add regression tests for #29859. However #29859 is not fully fixed.

src/test/compile-fail/traits-inductive-overflow-supertrait-oibit.rs

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+// 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.
+
+// OIBIT-based version of #29859, supertrait version. Test that using
+// a simple OIBIT `..` impl alone still doesn't allow arbitary bounds
+// to be synthesized.
+
+#![feature(optin_builtin_traits)]
+
+trait Magic: Copy {}
+impl Magic for .. {}
+
+fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
+
+#[derive(Debug)]
+struct NoClone;
+
+fn main() {
+    let (a, b) = copy(NoClone); //~ ERROR E0277
+    println!("{:?} {:?}", a, b);
+}

src/test/compile-fail/traits-inductive-overflow-supertrait.rs

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+// 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.
+
+// Regression test for #29859, supertrait version. This example
+// allowed arbitrary trait bounds to be synthesized.
+
+trait Magic: Copy {}
+impl<T: Magic> Magic for T {}
+
+fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
+
+#[derive(Debug)]
+struct NoClone;
+
+fn main() {
+    let (a, b) = copy(NoClone); //~ ERROR E0275
+    println!("{:?} {:?}", a, b);
+}

src/test/compile-fail/traits-inductive-overflow-two-traits.rs

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+// 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.
+
+// Regression test for #29859, initial version. This example allowed
+// arbitrary trait bounds to be synthesized.
+
+// Trait that you want all types to implement.
+use std::marker::{Sync as Trait};
+
+pub trait Magic {
+    type X: Trait;
+}
+impl<T: Magic> Magic for T {
+    type X = Self;
+}
+
+fn check<T: Trait>() {}
+
+fn wizard<T: Magic>() { check::<<T as Magic>::X>(); }
+
+fn main() {
+    wizard::<*mut ()>(); //~ ERROR E0275
+    // check::<*mut ()>();
+}