Files with + characted are not served from asset line.

[gorn]

Steps to reproduce

In development mode put a file at /assets/images/pin-m+.png

Expected behavior

File is served at http://railsapp.server.com/assets/pin-m+.png

Actual behavior

Error No route matches [GET] "/assets/pin-m+.png" occurs

System configuration

Rails version: 5.1.6.1

Ruby version: 2.5.1

[gorn]

It looks simillar to #9788

[y-yagi]

This is an issue of sprockets.
The sprockets use Rack::Utils.unescape for an escape path and Rack::Utils.unescape use URI.decode_www_form_component. So + converted to space.
https://github.com/rails/sprockets/blob/e25e0f5f993cbdff685a33540bbee927a4567177/lib/sprockets/server.rb#L38
https://github.com/rack/rack/blob/690f2276673b00935fffe8961431b462dfa65346/lib/rack/utils.rb#L52-L54

In my understanding, the reason for the escape is rack's specification. Please see rack/rack#265 for more details.
Anyway, this is not Rails's issue. So I close. Thanks.

[gorn]

This is completele against the principle od least surprise, so it needs to be at least documented.