Unmapping keys for a specific buffer(quickfix) only?

Question

I usually have j and k bound to gj and gk, respectively for navigating wrapped lines. But this becomes annoying when I have to use the quickfix window, so I thought of using something like :

augroup QuickFix
     au FileType qf unmap j
     au FileType qf unmap k
augroup END

But this undoes the mapping for the main buffer as well, so I tried unmap <buffer> j and unmap <buffer> k instead but this produces an E31: No such mapping error and the gk, gj bindings still seem to persist. The command that I am testing this using is :vimgrep "TODO" %.

Answer 1

Instead of unmap I simply did a buffer-local (:h :map-local) mapping back to the original values...

augroup QuickFix
     au FileType qf map <buffer> j j
     au FileType qf map <buffer> k k
augroup END

Ran vimgrep per your example and in the quickfix window I have j/k behavior while still maintaining gj/gk function in the main window.

Update: Interesting (and somewhat lengthy) side bar regarding the mapping commands used above. @LucHermite asked a valid question in the comments: "Shouldn't [the auto commands use] noremap?" He asked because what happens with map and the other non-noremap mapping commands is that keys on the RHS of a defined mapping retain any mappings they already have. This can actually result in a kind of "infinite loop" where a LHS key triggers a RHS key that is mapped to the LHS key which triggers the mapped keys again and repeat, ad infinitum.

It seems pretty clear then that map j j should result in just such an endless cycle. But it works fine. How? Well, there is a specific exception to the behavior I described which is noted in :h recursive_mapping:

If the {rhs} starts with {lhs}, the first character is not mapped again. For example:

:map ab abcd

will execute the "a" command and insert "bcd" in the text. The "ab" in the {rhs} will not be mapped again.

That being said, I'm normally a stickler for using the noremap commands. I just kind of locked in on the fact that map works correctly and answers OP's question but noremap is better because, at the very least, it's a good idea to get in the habit of using it always unless you know explicitly that you need map.

TL;DR: Though both are valid I recommend using noremap instead of map in the auto commands above.