error[E0283]: type annotations needed
  --> $DIR/issue-29147.rs:21:13
   |
LL |     let _ = <S5<_>>::xxx;
   |             ^^^^^^^^^^^^ cannot infer type for struct `S5<_>`
   |
note: multiple `impl`s satisfying `S5<_>: Foo` found
  --> $DIR/issue-29147.rs:17:1
   |
LL | impl Foo for S5<u32> { fn xxx(&self) {} }
   | ^^^^^^^^^^^^^^^^^^^^
LL | impl Foo for S5<u64> { fn xxx(&self) {} }
   | ^^^^^^^^^^^^^^^^^^^^
note: required by `Foo::xxx`
  --> $DIR/issue-29147.rs:10:13
   |
LL | trait Foo { fn xxx(&self); }
   |             ^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0283`.