Flash messages discarded unless kept

[matthewmcgarvey]

Purpose

Fixes #1271

Description

Previously, flash messages written to the session by default and used in the next request. That led to seeing flashes twice if both requests rendered HTML. Now, we only pass flash messages onto the next request if flash.keep is called. Luckily, we call that when actions redirect

lucky/src/lucky/redirectable.cr

Lines 122 to 124 in cff93b3

	def redirect(to path : String, status : Int32 = 302) : Lucky::TextResponse
	# flash messages are not consumed here, so keep them for the next action
	flash.keep

So, the two scenarios should be covered to avoid flash message duplicates. If flashes are set in an action that immediately renders HTML then they are discarded after, but if the action redirects the flash messages will carry over and continue carrying over until HTML is rendered.

I'm slightly wary of this because we are depending on code scattered across the library but I believe this is better than what we have right now.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[jwoertink]

Ah nice. This makes sense to me 👍 And good call on the redirect since we already have flash.keep in there.