Gem install with custom source builds wrong gem URI

[dudarenko-io]

I'm having a problem with running gem install using custom spec source.
I've add custom gem server source:

$ gem source --add 'https://nexus.company.com/repository/rubygems'
$ gem source -c

Then trying to install gem that surely exists on the server on url 'https://nexus.tcsbank.ru/repository/rubygems/gems/my_gem-0.1.0.gem'.

$ gem install my_gem
Traceback (most recent call last):
	6: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/request_set.rb:173:in `block (2 levels) in install'
	5: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/resolver/specification.rb:112:in `download'
	4: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/source.rb:213:in `download'
	3: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/remote_fetcher.rb:146:in `download'
	2: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/remote_fetcher.rb:285:in `cache_update_path'
	1: from /Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/remote_fetcher.rb:248:in `fetch_path'
/Users/User/.rbenv/versions/2.7.4/lib/ruby/site_ruby/2.7.0/rubygems/remote_fetcher.rb:232:in `fetch_http': bad response Repository not found 404 (https://nexus.company.ru/repository/gems/my_gem-0.1.0.gem) (Gem::RemoteFetcher::FetchError)
ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)
    bad response Repository not found 404 (https://nexus.tcsbank.ru/repository/gems/my_gem-0.1.0.gem)

Notice bad url 'https://nexus.tcsbank.ru/repository/gems/my_gem-0.1.0.gem'. Rubygem builds wrong uri from source url and gem path. It happens at remote_fetcher.rb:144

This issue is related to:

• Network problems
• Installing a library
• Publishing a library
• The command line gem
• Other

Here are my current environment details:

$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 3.2.27
  - RUBY VERSION: 2.7.4 (2021-07-07 patchlevel 191) [x86_64-darwin20]
  - INSTALLATION DIRECTORY: /Users/User/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0
  - USER INSTALLATION DIRECTORY: /Users/User/.gem/ruby/2.7.0
  - RUBY EXECUTABLE: /Users/User/.rbenv/versions/2.7.4/bin/ruby
  - GIT EXECUTABLE: /usr/bin/git
  - EXECUTABLE DIRECTORY: /Users/User/.rbenv/versions/2.7.4/bin
  - SPEC CACHE DIRECTORY: /Users/User/.local/share/gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: /Users/User/.rbenv/versions/2.7.4/etc
  - RUBYGEMS PLATFORMS:
     - ruby
     - x86_64-darwin-20
  - GEM PATHS:
     - /Users/User/.rbenv/versions/2.7.4/lib/ruby/gems/2.7.0
     - /Users/User/.gem/ruby/2.7.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
     - https://nexus.company.com/repository/rubygems
  - SHELL PATH:
     - /Users/User/.rbenv/versions/2.7.4/bin
     - /usr/local/Cellar/rbenv/1.1.2/libexec
     - /Users/User/.rbenv/shims
     - /usr/local/bin
     - /usr/bin
     - /bin
     - /usr/sbin
     - /sbin
     - /Library/Apple/usr/bin

I will abide by the code of conduct.

[dudarenko-io]

Note about URI concat method (alias of URI#merge)

irb(main):003:0> uri = URI.parse('https://example.com/1/2')
=> #<URI::HTTPS https://example.com/1/2>
irb(main):004:0> uri + '3'
=> #<URI::HTTPS https://example.com/1/3>
irb(main):005:0> uri + '/3'
=> #<URI::HTTPS https://example.com/3>

[deivid-rodriguez]

It seems similar to #1829. Does it work if you add a trailing slash to the source? It should be an easy fix similar to #3123, a pull request would be super appreciated!