Stable ICE: &mut request::Request<'mw, B, D> was a subtype of &mut request::Request<'_, _, _> but now is not?

[jolhoeft]

I've triggered an ICE with rust 1.21.0. There seem to be a few similar reports, but they are either Beta, or fairly old. I triggered this as part of migrating nickel to hyper 0.11. I committed the code that triggers this on my fork of nickel on branch async_402. See jolhoeft/nickel.rs@d0ccf03 (in file https://github.com/jolhoeft/nickel.rs/blob/d0ccf03e57a9d37307e15f5947d6cc69b32a9031/src/body_parser.rs)

(this branch still needs a lot of work, so normal compile errors are expected)

error: internal compiler error: /checkout/src/librustc_typeck/check/method/confirm.rs:345: &mut request::Request<'mw, B, D> was a subtype of &mut request::Request<'_, _, _> but now is not?
  --> src/body_parser.rs:81:14
   |
81 |         self.get_ref::<FormBodyParser>().map_err(|e| (StatusCode::BadRequest, e))
   |              ^^^^^^^

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.21.0 (3b72af97e 2017-10-09) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:437:8
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:381
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:391
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:611
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::span_bug
   7: rustc::session::opt_span_bug_fmt::{{closure}}
   8: rustc::session::span_bug_fmt
   9: rustc_typeck::check::FnCtxt::check_method_call
  10: rustc_typeck::check::FnCtxt::check_expr_kind
  11: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  12: rustc_typeck::check::FnCtxt::check_method_call
  13: rustc_typeck::check::FnCtxt::check_expr_kind
  14: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  15: rustc_typeck::check::FnCtxt::check_block_with_expected::{{closure}}
  16: rustc_typeck::check::FnCtxt::check_block_with_expected
  17: rustc_typeck::check::FnCtxt::check_expr_kind
  18: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_lvalue_pref
  19: rustc_typeck::check::FnCtxt::check_return_expr
  20: rustc_typeck::check::check_fn
  21: rustc_typeck::check::typeck_tables_of::{{closure}}
  22: rustc_typeck::check::typeck_tables_of
  23: rustc::dep_graph::graph::DepGraph::with_task
  24: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
  25: rustc::ty::maps::TyCtxtAt::typeck_tables_of
  26: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_tables_of
  27: rustc_typeck::check::typeck_item_bodies
  28: rustc::dep_graph::graph::DepGraph::with_task
  29: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
  30: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
  31: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  32: rustc_typeck::check_crate
  33: rustc::ty::context::TyCtxt::create_and_enter
  34: rustc_driver::driver::compile_input
  35: rustc_driver::run_compiler

[jolhoeft]

The following change got rid of the ICE for me:

index 7e15671..90c3622 100644
--- a/src/body_parser.rs
+++ b/src/body_parser.rs
@@ -76,7 +76,7 @@ pub trait FormBody {
 }
 
 #[deprecated(since = "0.11.0", note="Synchronizes async code with performance impact, will be removed in 0.12")]
-impl<'mw, B: Stream<Item=Chunk, Error=HyperError>, D> FormBody for Request<'mw, B, D> {
+impl<'mw, D> FormBody for Request<'mw, Body, D> {
     fn form_body(&mut self) -> Result<&Params, (StatusCode, BodyError)> {
         self.get_ref::<FormBodyParser>().map_err(|e| (StatusCode::BadRequest, e))
     }
@@ -88,7 +88,7 @@ pub trait JsonBody {
 }
 
 #[deprecated(since = "0.11.0", note="Synchronizes async code with performance impact, will be removed in 0.12")]
-impl<'mw, B: Stream<Item=Chunk, Error=HyperError>, D> JsonBody for Request<'mw, B, D> {
+impl<'mw, D> JsonBody for Request<'mw, Body, D> {
     // FIXME: Update the error type.
     // Would be good to capture parsing error rather than a generic io::Error.
     // FIXME: Do the content-type check

[kennytm]

Looks like a duplicate of #36701.