I've found the change in git, but it doesn't reference any discussion about it:
https://github.com/rust-lang/rust/commit/3816e57fd2a8ab19e4ac6d4b3ddd5b49d5973ff2
https://github.com/rust-lang/rust/commit/6510f1ce7cb026ceb98689583c13f18c1e7c2c12
I've found the change in git, but it doesn't reference any discussion about it:
https://github.com/rust-lang/rust/commit/3816e57fd2a8ab19e4ac6d4b3ddd5b49d5973ff2
https://github.com/rust-lang/rust/commit/6510f1ce7cb026ceb98689583c13f18c1e7c2c12