Added a swap-test for an edge case in path change recovery.

Author: ibabushkin

tests/cases/swap/new.rs

@@ -0,0 +1,7 @@
+pub mod a {
+    pub use super::b::Abc;
+}
+
+pub mod b {
+    pub struct Abc;
+}

tests/cases/swap/old.rs

@@ -0,0 +1,7 @@
+pub mod a {
+    pub struct Abc;
+}
+
+pub mod b {
+    pub use super::a::Abc;
+}

tests/cases/swap/stdout

@@ -0,0 +1 @@
+version bump: 1.0.0 -> (patch) -> 1.0.1

tests/cases/traits/dump

@@ -0,0 +1,12 @@
+13:28:48 eddyb | you need a fulfillment context that you put in all the bounds of the new item
+13:28:59 eddyb | (and assuming you used the translated old bounds as the ParamEnv)
+13:29:11 eddyb | (or rather, translated tcx.param_env(old_def_id))
+13:29:30 eddyb | you should be able to call the resolve_or_error or whatever it is thing
+13:29:55 eddyb | once you do that, impls are pretty easy
+13:30:03   twk | no, I didn't yet do this :P. But it seems I'll find most of what I need from browsing ParamEnv and friends
+13:30:20 eddyb | rustc::traits::fulfill
+13:30:22 eddyb | that's the important part
+13:31:07   twk | okay, I'll report back once there's something which doesn't fall over all the time
+13:31:09 eddyb | so for impls: for every old impl, e.g. impl Trait for X, check that X: Trait still holds, after translating (both X and Trait) to the new
+13:31:37 eddyb | it's the same fulfillment context thing as making sure the bounds are satisfied
+13:31:48   twk | hm, okay

tests/examples.rs

@@ -111,5 +111,6 @@ test!(regions, "tests/cases/regions");
 test!(removal, "tests/cases/removal");
 test!(removal_path, "tests/cases/removal_path");
 test!(structs, "tests/cases/structs");
+test!(swap, "tests/cases/swap");
 test!(traits, "tests/cases/traits");
 test!(ty_alias, "tests/cases/ty_alias");