Test for (previously uncaught) infinite loop identified by matthewjasper.

src/test/ui/issue-45696-no-variant-box-recur.rs

@@ -0,0 +1,66 @@
+// 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.
+
+// rust-lang/rust#45696: This test checks the compiler won't infinite
+// loop when you declare a variable of type `struct A(Box<A>, ...);`
+// (which is impossible to construct but *is* possible to declare; see
+// also issues #4287, #44933, and #52852).
+//
+// We will explicitly test AST-borrowck, NLL, and migration modes;
+// thus we will also skip the automated compare-mode=nll.
+
+// revisions: ast nll migrate
+// ignore-compare-mode-nll
+
+#![cfg_attr(nll, feature(nll))]
+//[migrate]compile-flags: -Z borrowck=migrate -Z two-phase-borrows
+
+// run-pass
+
+// This test has structs and functions that are by definiton unusable
+// all over the place, so just go ahead and allow dead_code
+#![allow(dead_code)]
+
+// direct regular recursion with indirect ownership via box
+struct C { field: Box<C> }
+
+// direct non-regular recursion with indirect ownership via box
+struct D { field: Box<(D, D)> }
+
+// indirect regular recursion with indirect ownership via box.
+struct E { field: F }
+struct F { field: Box<E> }
+
+// indirect non-regular recursion with indirect ownership via box.
+struct G { field: (F, F) }
+struct H { field: Box<E> }
+
+// These enums are cases that are not currently hit by the
+// `visit_terminator_drop` recursion down a type's structural
+// definition.
+//
+// But it seems prudent to include them in this test as variants on
+// the above, in that they are similarly non-constructable data types
+// with destructors that would diverge.
+enum I { One(Box<I>) }
+enum J { One(Box<J>), Two(Box<J>) }
+
+fn impossible_to_call_c(_c: C) { }
+fn impossible_to_call_d(_d: D) { }
+fn impossible_to_call_e(_e: E) { }
+fn impossible_to_call_f(_f: F) { }
+fn impossible_to_call_g(_g: G) { }
+fn impossible_to_call_h(_h: H) { }
+fn impossible_to_call_i(_i: I) { }
+fn impossible_to_call_j(_j: J) { }
+
+fn main() {
+
+}