error: Since extern blocks, unlike traits, don't have name, mock type name cannot be inferred and must be given explicitly for extern blocks:

           #[mocked(ExternMock)]
           extern { ... }
 --> $DIR/extern_block_name.rs:3:1
  |
3 | #[mocked]
  | ^^^^^^^^^
  |
  = note: this error originates in the attribute macro `mocked` (in Nightly builds, run with -Z macro-backtrace for more info)