Merge #7522

7522: Improve platform specific gem resolution r=deivid-rodriguez a=kou

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

Platform specific gems aren't resolved when platform specific gems are conflicted.

For example, in the following situation, foo-1.0.0-x64-mingw32 that requires bar<1 is conflicted because there is no bar<1. Without this change, Bundler raises a conflict error. But users can use foo-1.0.0 (no x64-mingw32) in this situation. With this change, Bundler resolves to foo-1.0.0 (no x64-mingw32).

```ruby
@index = build_index do
  gem "bar", "1.0.0"
  gem "foo", "1.0.0"
  gem "foo", "1.0.0", "x64-mingw32" do
    dep "bar", "< 1"
  end
end
dep "foo"
platforms "x64-mingw32"
````

See also #6247. This change includes the specs that were added in #6247.

### What was your diagnosis of the problem?

Not platform specific gem (foo-1.0.0 in the above case) isn't tried to be resolved when platform specific gem (foo-1.0.0-x64-mingw32 in the above case) is available.

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

In this PR, not platform specific gem (foo-1.0.0 in the above case) is also tried to be resolved even when platform specific gem (foo-1.0.0-x64-mingw32 in the above case) is available. Priority is "platform specific gem" -> "not platform specific gem". So platform specific gem is usable, platform specific gem is used. Not platform specific gem is used as fallback.

`search_for` represents this. Here is the `search_for` specification:
https://github.com/bundler/bundler/blob/master/lib/bundler/vendor/molinillo/lib/molinillo/modules/specification_provider.rb#L11-L13

> Search for the specifications that match the given dependency. The specifications in the returned array will be considered in reverse order, so the latest version ought to be last.

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

I choose this fix because this is based on Molinillo's specification.

Co-authored-by: Lars Kanis <lars@greiz-reinsdorf.de>
Co-authored-by: Samuel Giddins <segiddins@segiddins.me>
Co-authored-by: Sutou Kouhei <kou@clear-code.com>

1 files changed, 26 insertions, 5 deletions

diff --git a/lib/bundler/resolver/spec_group.rb b/lib/bundler/resolver/spec_group.rb
index e5772eed81..d5d12f7a2d 100644
--- a/lib/bundler/resolver/spec_group.rb
+++ b/lib/bundler/resolver/spec_group.rb
@@ -9,6 +9,7 @@ module Bundler
       attr_accessor :ignores_bundler_dependencies
 
       def initialize(all_specs)
+        @all_specs = all_specs
         raise ArgumentError, "cannot initialize with an empty value" unless exemplary_spec = all_specs.first
         @name = exemplary_spec.name
         @version = exemplary_spec.version
@@ -28,7 +29,7 @@ module Bundler
           lazy_spec = LazySpecification.new(name, version, s.platform, source)
           lazy_spec.dependencies.replace s.dependencies
           lazy_spec
-        end.compact
+        end.compact.uniq
       end
 
       def activate_platform!(platform)
@@ -37,13 +38,25 @@ module Bundler
         @activated_platforms << platform
       end
 
+      def copy_for(platform)
+        copied_sg = self.class.new(@all_specs)
+        copied_sg.ignores_bundler_dependencies = @ignores_bundler_dependencies
+        return nil unless copied_sg.for?(platform)
+        copied_sg.activate_platform!(platform)
+        copied_sg
+      end
+
+      def spec_for(platform)
+        @specs[platform]
+      end
+
       def for?(platform)
-        spec = @specs[platform]
-        !spec.nil?
+        !spec_for(platform).nil?
       end
 
       def to_s
-        @to_s ||= "#{name} (#{version})"
+        activated_platforms_string = sorted_activated_platforms.join(", ")
+        "#{name} (#{version}) (#{activated_platforms_string})"
       end
 
       def dependencies_for_activated_platforms
@@ -58,6 +71,7 @@ module Bundler
         return unless other.is_a?(SpecGroup)
         name == other.name &&
           version == other.version &&
+          sorted_activated_platforms == other.sorted_activated_platforms &&
           source == other.source
       end
 
@@ -65,11 +79,18 @@ module Bundler
         return unless other.is_a?(SpecGroup)
         name.eql?(other.name) &&
           version.eql?(other.version) &&
+          sorted_activated_platforms.eql?(other.sorted_activated_platforms) &&
           source.eql?(other.source)
       end
 
       def hash
-        to_s.hash ^ source.hash
+        name.hash ^ version.hash ^ sorted_activated_platforms.hash ^ source.hash
+      end
+
+    protected
+
+      def sorted_activated_platforms
+        @activated_platforms.sort_by(&:to_s)
       end
 
     private