[rubygems/rubygems] fix Gem::Dependency#to_spec returning nil when prerelease is the only available version

https://github.com/rubygems/rubygems/commit/a7dcc7214b

lib/rubygems/dependency.rb

@@ -330,7 +330,7 @@ class Gem::Dependency
     unless prerelease?
       # Move prereleases to the end of the list for >= 0 requirements
       pre, matches = matches.partition {|spec| spec.version.prerelease? }
-      matches += pre if requirement == Gem::Requirement.default
+      matches += pre if requirement == Gem::Requirement.default || matches.empty?
     end
 
     matches.first

test/rubygems/test_gem_dependency.rb

@@ -394,6 +394,16 @@ class TestGemDependency < Gem::TestCase
     assert_match "Could not find 'b' (= 2.0) among 1 total gem(s)", e.message
   end
 
+  def test_to_spec_with_only_prereleases
+    a_2_a_1 = util_spec "a", "2.a1"
+    a_2_a_2 = util_spec "a", "2.a2"
+    install_specs a_2_a_1, a_2_a_2
+
+    a_dep = dep "a", ">= 1"
+
+    assert_equal a_2_a_2, a_dep.to_spec
+  end
+
   def test_identity
     assert_equal dep("a", "= 1").identity, :released
     assert_equal dep("a", "= 1.a").identity, :complete

test/rubygems/test_gem_specification.rb

@@ -3801,6 +3801,13 @@ end
     assert Gem::Specification.find_by_name "q"
   end
 
+  def test_find_by_name_with_only_prereleases_with_requirements
+    q = util_spec "q", "2.a"
+    install_specs q
+
+    assert Gem::Specification.find_by_name "q", ">= 1"
+  end
+
   def test_find_by_name_prerelease
     b = util_spec "b", "2.a"