Can we deprecate guides(... = FALSE)?

[yutannihilation]

I happened to know guides() accepts FALSE as an option not to show the legend. e.g https://stackoverflow.com/a/14604540

p + guides(colour = FALSE)

I think none of the official documentation refers to this usage, and no test is broken if I remove this isFALSE(guide), so I think this is safe to remove. At least we should start encouraging people to use "none" as it is the supposed way. The only concern is that I cannot understand what this comment exactly means.... This has been here for 9 years since the point where the S3 guide system was born (0795c6f)...

ggplot2/R/guides-.r

Lines 187 to 190 in b4e3aea

	# this should be changed to testing guide == "none"
	# scale$legend is backward compatibility
	# if guides(XXX=FALSE), then scale_ZZZ(guides=XXX) is discarded.
	if (identical(guide, "none") || isFALSE(guide) || inherits(guide, "guide_none")) next

[yutannihilation]

OK, I found the history. legend = FALSE is an ancient syntax on scale_*() functions, which was deprecated by #265 and then removed (now we only get Ignoring unknown parameters: legend if we specify it). This cryptic comment had been placed before hadley proposed deprecating guide = FALSE. Now the allowed way is to specify show.legend = FALSE which doesn't conflict with the process of guide_train().

kohske@0795c6f#r363769