Auto merge of #6647 - bundler:segiddins/conflict-message-improvements, r=indirect

Make version conflict messages better

~~This is a WIP. Need to wait until https://github.com/CocoaPods/Molinillo/pull/99 is merged & released~~

### What was the end-user problem that led to this PR?

The problem was Bundler version messages could be confusing.

Closes https://github.com/bundler/bundler/issues/6642
Closes https://github.com/bundler/bundler/issues/6620

### What was your diagnosis of the problem?

My diagnosis was we barf out a bunch of "conflicts", not all of which are actually conflicts. We could also print a whole bunch of requirements that didn't _actually_ contribute to the conflict at hand.

Messaging was also super weird when there were `required_ruby_version` conflicts, since we called "ruby" a gem.

### What is your fix for the problem, implemented in this PR?

Improves Bundler version conflict messages in multiple cases. (conflict on `required_ruby_version`, conflict on 2.0 containing redundant platforms, conflict on 2.0 not being reduced to minimal form, showing irrelevant conflicts that dont actually conflict, actually reducing all type of conflicts to the minimal set).

### Why did you choose this fix out of the possible options?

I chose this fix because...

9 files changed, 101 insertions, 27 deletions

diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index df8ee1f54b..3964c07fb5 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -855,8 +855,8 @@ module Bundler
           concat_ruby_version_requirements(locked_ruby_version_object) unless @unlock[:ruby]
         end
         [
-          Dependency.new("ruby\0", ruby_versions),
-          Dependency.new("rubygems\0", Gem::VERSION),
+          Dependency.new("Ruby\0", ruby_versions),
+          Dependency.new("RubyGems\0", Gem::VERSION),
         ]
       end
     end
diff --git a/lib/bundler/resolver.rb b/lib/bundler/resolver.rb
index 8872b861be..3fd1706371 100644
--- a/lib/bundler/resolver.rb
+++ b/lib/bundler/resolver.rb
@@ -302,10 +302,23 @@ module Bundler
     end
 
     def version_conflict_message(e)
+      # only show essential conflicts, if possible
+      conflicts = e.conflicts.dup
+      conflicts.delete_if do |_name, conflict|
+        deps = conflict.requirement_trees.map(&:last).flatten(1)
+        !Bundler::VersionRanges.empty?(*Bundler::VersionRanges.for_many(deps.map(&:requirement)))
+      end
+      e = Molinillo::VersionConflict.new(conflicts, e.specification_provider) unless conflicts.empty?
+
+      solver_name = "Bundler"
+      possibility_type = "gem"
       e.message_with_trees(
-        :solver_name => "Bundler",
-        :possibility_type => "gem",
+        :solver_name => solver_name,
+        :possibility_type => possibility_type,
         :reduce_trees => lambda do |trees|
+          # called first, because we want to reduce the amount of work required to find maximal empty sets
+          trees.uniq! {|t| t.flatten.map {|dep| [dep.name, dep.requirement] } }
+
           # bail out if tree size is too big for Array#combination to make any sense
           return trees if trees.size > 15
           maximal = 1.upto(trees.size).map do |size|
@@ -313,10 +326,8 @@ module Bundler
           end.flatten(1).select do |deps|
             Bundler::VersionRanges.empty?(*Bundler::VersionRanges.for_many(deps.map(&:requirement)))
           end.min_by(&:size)
-          trees.reject! {|t| !maximal.include?(t.last) } if maximal
 
-          trees = trees.sort_by {|t| t.flatten.map(&:to_s) }
-          trees.uniq! {|t| t.flatten.map {|dep| [dep.name, dep.requirement] } }
+          trees.reject! {|t| !maximal.include?(t.last) } if maximal
 
           trees.sort_by {|t| t.reverse.map(&:name) }
         end,
@@ -351,7 +362,11 @@ module Bundler
               []
             end.compact.map(&:to_s).uniq.sort
 
-            o << "Could not find gem '#{SharedHelpers.pretty_dependency(conflict.requirement)}'"
+            metadata_requirement = name.end_with?("\0")
+
+            o << "Could not find gem '" unless metadata_requirement
+            o << SharedHelpers.pretty_dependency(conflict.requirement)
+            o << "'" unless metadata_requirement
             if conflict.requirement_trees.first.size > 1
               o << ", which is required by "
               o << "gem '#{SharedHelpers.pretty_dependency(conflict.requirement_trees.first[-2])}',"
@@ -360,12 +375,21 @@ module Bundler
 
             o << if relevant_sources.empty?
                    "in any of the sources.\n"
+                 elsif metadata_requirement
+                   "is not available in #{relevant_sources.join(" or ")}"
                  else
                    "in any of the relevant sources:\n  #{relevant_sources * "\n  "}\n"
                  end
           end
         end,
-        :version_for_spec => lambda {|spec| spec.version }
+        :version_for_spec => lambda {|spec| spec.version },
+        :incompatible_version_message_for_conflict => lambda do |name, _conflict|
+          if name.end_with?("\0")
+            %(#{solver_name} found conflicting requirements for the #{name} version:)
+          else
+            %(#{solver_name} could not find compatible versions for #{possibility_type} "#{name}":)
+          end
+        end
       )
     end
 
diff --git a/lib/bundler/resolver/spec_group.rb b/lib/bundler/resolver/spec_group.rb
index 34d043aed7..119f63b5c8 100644
--- a/lib/bundler/resolver/spec_group.rb
+++ b/lib/bundler/resolver/spec_group.rb
@@ -94,10 +94,10 @@ module Bundler
         return [] if !spec.is_a?(EndpointSpecification) && !spec.is_a?(Gem::Specification)
         dependencies = []
         if !spec.required_ruby_version.nil? && !spec.required_ruby_version.none?
-          dependencies << DepProxy.new(Gem::Dependency.new("ruby\0", spec.required_ruby_version), platform)
+          dependencies << DepProxy.new(Gem::Dependency.new("Ruby\0", spec.required_ruby_version), platform)
         end
         if !spec.required_rubygems_version.nil? && !spec.required_rubygems_version.none?
-          dependencies << DepProxy.new(Gem::Dependency.new("rubygems\0", spec.required_rubygems_version), platform)
+          dependencies << DepProxy.new(Gem::Dependency.new("RubyGems\0", spec.required_rubygems_version), platform)
         end
         dependencies
       end
diff --git a/lib/bundler/source/metadata.rb b/lib/bundler/source/metadata.rb
index 93909002c7..ff8861c710 100644
--- a/lib/bundler/source/metadata.rb
+++ b/lib/bundler/source/metadata.rb
@@ -5,8 +5,10 @@ module Bundler
     class Metadata < Source
       def specs
         @specs ||= Index.build do |idx|
-          idx << Gem::Specification.new("ruby\0", RubyVersion.system.to_gem_version_with_patchlevel)
-          idx << Gem::Specification.new("rubygems\0", Gem::VERSION)
+          idx << Gem::Specification.new("Ruby\0", RubyVersion.system.to_gem_version_with_patchlevel)
+          idx << Gem::Specification.new("RubyGems\0", Gem::VERSION) do |s|
+            s.required_rubygems_version = Gem::Requirement.default
+          end
 
           idx << Gem::Specification.new do |s|
             s.name     = "bundler"
diff --git a/lib/bundler/version_ranges.rb b/lib/bundler/version_ranges.rb
index ec25716cde..12a956d6a0 100644
--- a/lib/bundler/version_ranges.rb
+++ b/lib/bundler/version_ranges.rb
@@ -5,11 +5,42 @@ module Bundler
     NEq = Struct.new(:version)
     ReqR = Struct.new(:left, :right)
     class ReqR
-      Endpoint = Struct.new(:version, :inclusive)
+      Endpoint = Struct.new(:version, :inclusive) do
+        def <=>(other)
+          if version.equal?(INFINITY)
+            return 0 if other.version.equal?(INFINITY)
+            return 1
+          elsif other.version.equal?(INFINITY)
+            return -1
+          end
+
+          comp = version <=> other.version
+          return comp unless comp.zero?
+
+          if inclusive && !other.inclusive
+            1
+          elsif !inclusive && other.inclusive
+            -1
+          else
+            0
+          end
+        end
+      end
+
       def to_s
         "#{left.inclusive ? "[" : "("}#{left.version}, #{right.version}#{right.inclusive ? "]" : ")"}"
       end
-      INFINITY = Object.new.freeze
+      INFINITY = begin
+        inf = Object.new
+        def inf.to_s
+          "∞"
+        end
+        def inf.<=>(other)
+          return 0 if other.equal?(self)
+          1
+        end
+        inf.freeze
+      end
       ZERO = Gem::Version.new("0.a")
 
       def cover?(v)
@@ -32,6 +63,15 @@ module Bundler
         left.version == right.version
       end
 
+      def <=>(other)
+        return -1 if other.equal?(INFINITY)
+
+        comp = left <=> other.left
+        return comp unless comp.zero?
+
+        right <=> other.right
+      end
+
       UNIVERSAL = ReqR.new(ReqR::Endpoint.new(Gem::Version.new("0.a"), true), ReqR::Endpoint.new(ReqR::INFINITY, false)).freeze
     end
 
@@ -57,7 +97,7 @@ module Bundler
       end.uniq
       ranges, neqs = ranges.partition {|r| !r.is_a?(NEq) }
 
-      [ranges.sort_by {|range| [range.left.version, range.left.inclusive ? 0 : 1] }, neqs.map(&:version)]
+      [ranges.sort, neqs.map(&:version)]
     end
 
     def self.empty?(ranges, neqs)
@@ -66,8 +106,14 @@ module Bundler
         next false if curr_range.single? && neqs.include?(curr_range.left.version)
         next curr_range if last_range.right.version == ReqR::INFINITY
         case last_range.right.version <=> curr_range.left.version
-        when 1 then next curr_range
-        when 0 then next(last_range.right.inclusive && curr_range.left.inclusive && !neqs.include?(curr_range.left.version) && curr_range)
+        # higher
+        when 1 then next ReqR.new(curr_range.left, last_range.right)
+        # equal
+        when 0
+          if last_range.right.inclusive && curr_range.left.inclusive && !neqs.include?(curr_range.left.version)
+            ReqR.new(curr_range.left, [curr_range.right, last_range.right].max)
+          end
+        # lower
         when -1 then next false
         end
       end
diff --git a/spec/bundler/version_ranges_spec.rb b/spec/bundler/version_ranges_spec.rb
index ccbb9285d5..bca044b0c0 100644
--- a/spec/bundler/version_ranges_spec.rb
+++ b/spec/bundler/version_ranges_spec.rb
@@ -25,9 +25,12 @@ RSpec.describe Bundler::VersionRanges do
     include_examples "empty?", false, ">= 1.0.0", "< 2.0.0"
     include_examples "empty?", false, "~> 1"
     include_examples "empty?", false, "~> 2.0", "~> 2.1"
+    include_examples "empty?", true, ">= 4.1.0", "< 5.0", "= 5.2.1"
+    include_examples "empty?", true, "< 5.0", "< 5.3", "< 6.0", "< 6", "= 5.2.0", "> 2", ">= 3.0", ">= 3.1", ">= 3.2", ">= 4.0.0", ">= 4.1.0", ">= 4.2.0", ">= 4.2", ">= 4"
     include_examples "empty?", true, "!= 1", "< 2", "> 2"
     include_examples "empty?", true, "!= 1", "<= 1", ">= 1"
     include_examples "empty?", true, "< 2", "> 2"
+    include_examples "empty?", true, "< 2", "> 2", "= 2"
     include_examples "empty?", true, "= 1", "!= 1"
     include_examples "empty?", true, "= 1", "= 2"
     include_examples "empty?", true, "= 1", "~> 2"
diff --git a/spec/install/gems/resolving_spec.rb b/spec/install/gems/resolving_spec.rb
index e58f32836c..f581522c71 100644
--- a/spec/install/gems/resolving_spec.rb
+++ b/spec/install/gems/resolving_spec.rb
@@ -142,15 +142,14 @@ RSpec.describe "bundle install with install-time dependencies" do
           expect(out).to_not include("Gem::InstallError: require_ruby requires Ruby version > 9000")
 
           nice_error = strip_whitespace(<<-E).strip
-            Bundler could not find compatible versions for gem "ruby\0":
+            Bundler found conflicting requirements for the Ruby\0 version:
               In Gemfile:
-                ruby\0 (#{error_message_requirement})
+                Ruby\0 (#{error_message_requirement})
 
                 require_ruby was resolved to 1.0, which depends on
-                  ruby\0 (> 9000)
+                  Ruby\0 (> 9000)
 
-            Could not find gem 'ruby\0 (> 9000)', which is required by gem 'require_ruby', in any of the relevant sources:
-              the local ruby installation
+            Ruby\0 (> 9000), which is required by gem 'require_ruby', is not available in the local ruby installation
           E
           expect(last_command.bundler_err).to end_with(nice_error)
         end
diff --git a/spec/resolver/basic_spec.rb b/spec/resolver/basic_spec.rb
index 6d2dea2fb3..a2d5e13377 100644
--- a/spec/resolver/basic_spec.rb
+++ b/spec/resolver/basic_spec.rb
@@ -157,10 +157,10 @@ Bundler could not find compatible versions for gem "a":
         s.required_ruby_version = "~> 2.0.0"
       end
 
-      gem "ruby\0", "1.8.7"
+      gem "Ruby\0", "1.8.7"
     end
     dep "foo"
-    dep "ruby\0", "1.8.7"
+    dep "Ruby\0", "1.8.7"
 
     deps = []
     @deps.each do |d|
diff --git a/spec/support/indexes.rb b/spec/support/indexes.rb
index c56d6145a7..5f6c515735 100644
--- a/spec/support/indexes.rb
+++ b/spec/support/indexes.rb
@@ -76,7 +76,7 @@ module Spec
         gem "rack-mount", %w[0.4 0.5 0.5.1 0.5.2 0.6]
 
         # --- Pre-release support
-        gem "rubygems\0", ["1.3.2"]
+        gem "RubyGems\0", ["1.3.2"]
 
         # --- Rails
         versions "1.2.3 2.2.3 2.3.5 3.0.0.beta 3.0.0.beta1" do |version|
@@ -413,7 +413,7 @@ module Spec
         gem("b", %w[0.9.0 1.5.0 2.0.0.pre])
 
         # --- Pre-release support
-        gem "rubygems\0", ["1.3.2"]
+        gem "RubyGems\0", ["1.3.2"]
       end
     end
   end