first draft of program_clauses_for_env

This computes the transitive closure of traits that appear in the
environment and then appends their clauses. It needs some work, but
it's in the right direction.

src/test/ui/chalkify/lower_env1.rs

@@ -0,0 +1,24 @@
+// 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.
+
+#![feature(rustc_attrs)]
+#![allow(dead_code)]
+
+trait Foo { }
+
+#[rustc_dump_program_clauses] //~ ERROR program clause dump
+trait Bar where Self: Foo { }
+
+#[rustc_dump_env_program_clauses] //~ ERROR program clause dump
+fn bar<T: Bar>() {
+}
+
+fn main() {
+}

src/test/ui/chalkify/lower_env1.stderr

@@ -0,0 +1,24 @@
+error: program clause dump
+  --> $DIR/lower_env1.rs:16:1
+   |
+LL | #[rustc_dump_program_clauses] //~ ERROR program clause dump
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: Implemented(Self: Bar) :- FromEnv(Self: Bar).
+   = note: FromEnv(Self: Bar) :- FromEnv(Self: Bar).
+   = note: FromEnv(Self: Foo) :- FromEnv(Self: Bar).
+
+error: program clause dump
+  --> $DIR/lower_env1.rs:19:1
+   |
+LL | #[rustc_dump_env_program_clauses] //~ ERROR program clause dump
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: Implemented(Self: std::marker::Sized) :- FromEnv(Self: std::marker::Sized).
+   = note: Implemented(Self: Bar) :- FromEnv(Self: Bar).
+   = note: FromEnv(Self: Bar) :- FromEnv(Self: Bar).
+   = note: FromEnv(Self: Foo) :- FromEnv(Self: Bar).
+   = note: Implemented(Self: Foo) :- FromEnv(Self: Foo).
+
+error: aborting due to 2 previous errors
+