I filled in the OP with some of my own commentary, including around the reasoning for the ‘links’ / ‘foreign_links’ split (links have special pattern-matching / backtrace propagation capabilities that foreign_links don’t); and the definition of local error types / traits (coherence violations otherwise).
I moved the renaming of quick_error to an issue - it is plainly an implementation detail and should not be clobbering the quick_error crate.
The internal quick_error macro was just a way to get the quick_error syntax without figuring out how to write it myself. It supports syntax that error-chain doesn’t even use, so would be better to pare it down to something error-chain specific.