Installing themes requires install of outdated gems?

hi jekyll land,

i’m new to jekyll (and ruby), i’ve set it up locally on a debian machine to build a website that i’ll then push to a vps.

the problems i keep encountering is that after i download a theme (eg a zip from github) to set up my site, they often have dependency problems and wont run. i often get messages like this when i try to run bundle install in the theme dir:

"Bundler could not find compatible versions for gem "bundler":
  In Gemfile:
    bundler (~> 1.15)

  Current Bundler version:
    bundler (2.0.2)
This Gemfile requires a different version of Bundler.
Perhaps you need to update Bundler by running `gem install bundler`?

Could not find gem 'bundler (~> 1.15)' in any of the relevant sources:
  the local ruby installation"

and if i eg install the older bundler, then i end up with tons of duplicated gems, because the older versions are also added.

i had this happen on a few older themes so i thought they were broken, but then i just tried with the textlog theme which is not very old (https://github.com/heiswayi/textlog). it also happened with the hack-css theme. the gemfile.lock of hack-css declares that it was bundled with bundler 1.13.x. does that mean that the only way to use that theme is to downgrade bundler (+all dependencies)?

it’s got me thinking that it’s me going about things the wrong way. i’m able to set up a site correctly with the minima and jekyll-now and minimal-mistakes themes, by following the jekyll tutorials. but i didn’t want to go with any of those.

and if different themes require different versions of lots of gems, it seems like it would make changing themes a difficult business.

if anyone can enlighten me a little about any of this, i’d be grateful.

thx.