Remove dead Molinillo-era error classes and simplify DependencyResolutionError

Author: colby-swandale

Manifest.txt

@@ -470,7 +470,6 @@ lib/rubygems/resolver/api_set/gem_parser.rb
 lib/rubygems/resolver/api_specification.rb
 lib/rubygems/resolver/best_set.rb
 lib/rubygems/resolver/composed_set.rb
-lib/rubygems/resolver/conflict.rb
 lib/rubygems/resolver/current_set.rb
 lib/rubygems/resolver/dependency_request.rb
 lib/rubygems/resolver/git_set.rb

lib/rubygems/exceptions.rb

@@ -128,40 +128,6 @@ def initialize(name, version, errors = nil)
 
 Gem.deprecate_constant :SpecificGemNotFoundException
 
-##
-# Raised by Gem::Resolver when dependencies conflict and create the
-# inability to find a valid possible spec for a request.
-
-class Gem::ImpossibleDependenciesError < Gem::Exception
-  attr_reader :conflicts
-  attr_reader :request
-
-  def initialize(request, conflicts)
-    @request   = request
-    @conflicts = conflicts
-
-    super build_message
-  end
-
-  def build_message # :nodoc:
-    requester  = @request.requester
-    requester  = requester ? requester.spec.full_name : "The user"
-    dependency = @request.dependency
-
-    message = "#{requester} requires #{dependency} but it conflicted:\n".dup
-
-    @conflicts.each do |_, conflict|
-      message << conflict.explanation
-    end
-
-    message
-  end
-
-  def dependency
-    @request.dependency
-  end
-end
-
 class Gem::InstallError < Gem::Exception; end
 
 class Gem::RuntimeRequirementNotMetError < Gem::InstallError

lib/rubygems/resolver.rb

@@ -388,7 +388,6 @@ def make_logger
 end
 
 require_relative "resolver/activation_request"
-require_relative "resolver/conflict"
 require_relative "resolver/dependency_request"
 require_relative "resolver/requirement_list"
 require_relative "resolver/set"

lib/rubygems/resolver/conflict.rb

@@ -6,21 +6,16 @@ class TestGemDependencyResolutionError < Gem::TestCase
   def setup
     super
 
-    @spec = util_spec "a", 2
-
-    @a1_req = Gem::Resolver::DependencyRequest.new dep("a", "= 1"), nil
-    @a2_req = Gem::Resolver::DependencyRequest.new dep("a", "= 2"), nil
-
-    @activated = Gem::Resolver::ActivationRequest.new @spec, @a2_req
-
-    @conflict = Gem::Resolver::Conflict.new @a1_req, @activated
-
-    @error = Gem::DependencyResolutionError.new @conflict
+    failure = Struct.new(:explanation).new("a depends on b (= 1.0) but no versions match")
+    @error = Gem::DependencyResolutionError.new failure
   end
 
   def test_message
-    assert_match(/Activated a-2/, @error.message)
-    assert_match(/conflicting dependency/, @error.message)
+    assert_equal "a depends on b (= 1.0) but no versions match", @error.message
+  end
+
+  def test_explanation
+    assert_equal "a depends on b (= 1.0) but no versions match", @error.explanation
   end
 
   def test_conflict