counsel.el (counsel-colors--name-to-hex): protect against invalid input.

[mookid]

fix #1853

[basil-conto]

Better to use delq here.

[mookid]

yes, in fact it is probably better not to allocate two lists and use mapcan instead.

edit: this is misleading. delete does not copy.

[basil-conto]

It's not always clear when it's better to use (delq nil (mapcar ...)) vs mapcan. The thing about mapcan is it was only added in Emacs 25, so you have to use the wrapper cl-mapcan, and you still need to allocate a cons cell in the loop for each element you want to keep:

(cl-mapcan (lambda (cell)
             (let* ((name (car cell))
                    (dups (cdr cell))
                    (hex (counsel-colors--name-to-hex name)))
               (and hex (list (propertize name 'hex hex 'dups dups)))))
           (list-colors-duplicates))

Benchmarking the two approaches suggests delq+mapcar is a hair faster and smaller than cl-mapcan they're pretty evenly matched. I really don't mind either way, I'm just saying there are tradeoffs, so it basically comes down to personal preference.

[mookid]

Thanks for running the experimentation.

Note that contrary to what I said, delete is destructive and does not make a new list (but remove does).

[basil-conto]

Note that contrary to what I said, delete is destructive and does not make a new list (but remove does).

Yup. The difference between delq and delete is that the former only accepts lists and uses eq for equality, thus making it the standard function for use in (delq nil (mapcar ...)). Using delete is less common and reserved for cases where equivalence under equal is needed.

[abo-abo]

Thanks.