Specialized Drop impl causes 'internal compiler error'

[Lazarus535]

------------IMPORTANT----------------

I accedentally posted the issue for Cargo, but it is a rustc bug.
I already opened the correct issue for rustc:
rust-lang/rust#40132
Please just close! :-(

---

Problem:

rustc crashes with 'internal compiler error' if a special file (see the 'Input' section) is compiled.

Exact error output (run via cargo run):

[me@my_machine rustc_bug_1]$ cargo run
   Compiling rustc_bug_1 v0.1.0 (file:///home/me/some_folder/rustc_bug_1)
error: internal compiler error: /checkout/src/librustc_typeck/check/dropck.rs:650: substs for an impl must map types to TyParam

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

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:417
note: Run with `RUST_BACKTRACE=1` for a backtrace.

error: Could not compile `rustc_bug_1`.

To learn more, run the command again with --verbose.

How to reproduce the error:

1. Create a new (binary) project with cargo new rustc_bug_1 --bin

2. Put the attached source inside main.rs

3. Run the project with cargo run

4. Witness the error ;-)

The error-causeing source:

struct A<T> {
  a: T,
}

fn main() {
    struct Z {}

    let x: A<Z> = A{ a: Z{} };

    struct DropStruct;

    impl Drop for A<DropStruct> {
      fn drop(&mut self) {
        println!("I'm dropping an A<DropStruct>!");
      }
    }
}

Explanation:

I tried some crazy stuff in Rust in order to better understand the languages' semantics when i encountered the bug. I know....usually you cannot specialize the Drop impl, or so the compiler keeps telling me if i further minimize the provided source.

Used OS and rust toolchain:

Arch x64 (up2date)
Rust Toolchains:

stable-x86_64-unknown-linux-gnu
beta-x86_64-unknown-linux-gnu
nightly-x86_64-unknown-linux-gnu

Tested with all three.

[alexcrichton]

No worries for the accidental post to cargo :)