use param_env on the trait_cache key

[qmx]

We bailed from making trans_fulfill_obligation return Option or Result, just made it less prone to crashing outside trans

r? @nikomatsakis

[arielb1]

@bors r+

[bors]

📌 Commit 03d9056 has been approved by arielb1

[nikomatsakis]

Just a nit.

[nikomatsakis]

Nit: Can we extend this comment to say "/// Assumes that this is run after the entire crate has been successfully type-checked."

[alexcrichton]

@bors: r=nikomatsakis

[bors]

📌 Commit a7e302a has been approved by nikomatsakis

[bors]

⌛ Testing commit a7e302a33a634fdbadd01b71f97d964b3a6b31f4 with merge b88c670c31bd47a19d5cd788a1e5d7ab8e54d6f8...

[bors]

💔 Test failed - status-travis

[kennytm]

Needs to submit a PR to miri, and set miri's toolstate to "Broken". (cc @oli-obk @RalfJung @eddyb)

[00:47:34] error[E0061]: this function takes 3 parameters but 2 parameters were supplied
[00:47:34]     --> /checkout/src/tools/miri/src/librustc_mir/interpret/eval_context.rs:2419:45
[00:47:34]      |
[00:47:34] 2419 |     let vtbl = tcx.trans_fulfill_obligation(DUMMY_SP, ty::Binder(trait_ref));
[00:47:34]      |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 3 parameters
[00:47:34] 
[00:47:35] error: aborting due to previous error
[00:47:35] 
[00:47:35] error: Could not compile `rustc_miri`.

[nikomatsakis]

@bors r+

[bors]

📌 Commit 9d52cb2 has been approved by nikomatsakis

[bors]

⌛ Testing commit 9d52cb2 with merge 930d3b1...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 930d3b1 to master...