[rubygems/rubygems] Improve error output when removing a source through gem sources

"Not present in cache" felt a bit unclear, so I changed the reason to:

"No configured sources" or "source not present in configured sources",
also pointing explicitly to the configuration file where RubyGems is
looking for the source to be removed.

ruby/rubygems@2bae554eff

Author: deivid-rodriguez

lib/rubygems/commands/sources_command.rb

@@ -204,13 +204,15 @@ def execute
   def remove_source(source_uri) # :nodoc:
     source = Gem::Source.new source_uri
 
-    if Gem.sources.include? source
+    if configured_sources&.include? source
       Gem.sources.delete source
       Gem.configuration.write
 
       say "#{source_uri} removed from sources"
+    elsif configured_sources
+      say "source #{source_uri} cannot be removed because it's not present in #{config_file_name}"
     else
-      say "source #{source_uri} not present in cache"
+      say "source #{source_uri} cannot be removed because there are no configured sources in #{config_file_name}"
     end
   end
 
@@ -238,6 +240,13 @@ def remove_cache_file(desc, path) # :nodoc:
   private
 
   def configured_sources
-    Gem.configuration.sources
+    return @configured_sources if defined?(@configured_sources)
+
+    configuration_sources = Gem.configuration.sources
+    @configured_sources = Gem::SourceList.from(configuration_sources) if configuration_sources
+  end
+
+  def config_file_name
+    Gem.configuration.config_file_name
   end
 end

test/rubygems/test_gem_commands_sources_command.rb

@@ -424,6 +424,23 @@ def test_execute_remove_no_network
   end
 
   def test_execute_remove_not_present
+    Gem.configuration.sources = ["https://other.repo"]
+
+    @cmd.handle_options %W[--remove #{@new_repo}]
+
+    use_ui @ui do
+      @cmd.execute
+    end
+
+    expected = "source #{@new_repo} cannot be removed because it's not present in #{Gem.configuration.config_file_name}\n"
+
+    assert_equal expected, @ui.output
+    assert_equal "", @ui.error
+  ensure
+    Gem.configuration.sources = nil
+  end
+
+  def test_execute_remove_nothing_configured
     spec_fetcher
 
     @cmd.handle_options %W[--remove https://does.not.exist]
@@ -432,7 +449,7 @@ def test_execute_remove_not_present
       @cmd.execute
     end
 
-    expected = "source https://does.not.exist not present in cache\n"
+    expected = "source https://does.not.exist cannot be removed because there are no configured sources in #{Gem.configuration.config_file_name}\n"
 
     assert_equal expected, @ui.output
     assert_equal "", @ui.error