Improve platform specific gem resolution

It resolves #6247. This changes includes the patches that add (RSpec)
specs for this situation in #6247.

If there is a platform specific gem but it can't be resolved available
version, Bundler reports an error.

For example,

    @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"

raises an error because foo-1.0.0-x64-mingw32 requires bar<1 but there
isn't bar<1.

With this change, foo-1.0.0 (no x64-mingw32) is used as
fallback. Because foo-1.0.0 doesn't depend on bar<1.

1 files changed, 11 insertions, 0 deletions

diff --git a/spec/resolver/platform_spec.rb b/spec/resolver/platform_spec.rb
index 223320fe7b..9a97a2c67c 100644
--- a/spec/resolver/platform_spec.rb
+++ b/spec/resolver/platform_spec.rb
@@ -54,6 +54,17 @@ RSpec.describe "Resolving platform craziness" do
     should_resolve_as %w[foo-1.0.0]
   end
 
+  it "prefers the platform specific gem to the ruby version" do
+    @index = build_index do
+      gem "foo", "1.0.0"
+      gem "foo", "1.0.0", "x64-mingw32"
+    end
+    dep "foo"
+    platforms "x64-mingw32"
+
+    should_resolve_as %w[foo-1.0.0-x64-mingw32]
+  end
+
   it "takes the latest ruby gem if the platform specific gem doesn't match the required_ruby_version" do
     @index = build_index do
       gem "foo", "1.0.0"