[ruby/rubygems] Undeprecate `Gem::Version.new(nil)`

It seems like we were trying to deprecate passing `nil` to
Gem::Version.new.  This breaks existing code, and I don't think there is
a good reason to deprecate this usage.

I believe what we want to prevent is the following code:

```ruby
Gem::Specification.new do |spec|
  spec.version = nil
  # suddenly the spec version is 0!
  p spec.version
end
```

This commit allows people to manually construct `Gem::Version.new(nil)`,
but when someone assigns `nil` as the Gem specification version, it sets
the spec version to `nil` (making the specification invalid).  People
who manually construct `Gem::Version` objects and use nil should be
allowed to do it, and `Gem::Version.new(nil) == Gem::Version.new("0")`,
but people who assign `nil` in a gemspec will get an invalid gemspec.

I think deprecation started
[here](https://github.com/ruby/rubygems/pull/2203) but there doesn't
seem to be a reason to do it.

Fixes https://github.com/ruby/rubygems/pull/9052

https://github.com/ruby/rubygems/commit/ded5e909c2

5 files changed, 43 insertions, 55 deletions

diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index 4c5ecb8f79..a9ec6aa3a3 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -2517,7 +2517,7 @@ class Gem::Specification < Gem::BasicSpecification
   # Set the version to +version+.
 
   def version=(version)
-    @version = Gem::Version.create(version)
+    @version = version.nil? ? version : Gem::Version.create(version)
   end
 
   def stubbed?
diff --git a/lib/rubygems/version.rb b/lib/rubygems/version.rb
index 25c412be4b..c9fffc1cb7 100644
--- a/lib/rubygems/version.rb
+++ b/lib/rubygems/version.rb
@@ -171,9 +171,7 @@ class Gem::Version
   # True if the +version+ string matches RubyGems' requirements.
 
   def self.correct?(version)
-    nil_versions_are_discouraged! if version.nil?
-
-    ANCHORED_VERSION_PATTERN.match?(version.to_s)
+    version.nil? || ANCHORED_VERSION_PATTERN.match?(version.to_s)
   end
 
   ##
@@ -182,15 +180,10 @@ class Gem::Version
   #
   #   ver1 = Version.create('1.3.17')   # -> (Version object)
   #   ver2 = Version.create(ver1)       # -> (ver1)
-  #   ver3 = Version.create(nil)        # -> nil
 
   def self.create(input)
     if self === input # check yourself before you wreck yourself
       input
-    elsif input.nil?
-      nil_versions_are_discouraged!
-
-      nil
     else
       new input
     end
@@ -206,14 +199,6 @@ class Gem::Version
     @@all[version] ||= super
   end
 
-  def self.nil_versions_are_discouraged!
-    unless Gem::Deprecate.skip
-      warn "nil versions are discouraged and will be deprecated in Rubygems 4"
-    end
-  end
-
-  private_class_method :nil_versions_are_discouraged!
-
   ##
   # Constructs a Version from the +version+ string.  A version string is a
   # series of digits or ASCII letters separated by dots.
@@ -224,7 +209,7 @@ class Gem::Version
     end
 
     # If version is an empty string convert it to 0
-    version = 0 if version.is_a?(String) && /\A\s*\Z/.match?(version)
+    version = 0 if version.nil? || (version.is_a?(String) && /\A\s*\Z/.match?(version))
 
     @version = version.to_s
 
diff --git a/test/rubygems/test_gem_requirement.rb b/test/rubygems/test_gem_requirement.rb
index de0d11ec00..00634dc7f4 100644
--- a/test/rubygems/test_gem_requirement.rb
+++ b/test/rubygems/test_gem_requirement.rb
@@ -137,11 +137,7 @@ class TestGemRequirement < Gem::TestCase
     refute_satisfied_by "1.2", r
     assert_satisfied_by "1.3", r
 
-    assert_raise ArgumentError do
-      Gem::Deprecate.skip_during do
-        assert_satisfied_by nil, r
-      end
-    end
+    assert_satisfied_by nil, r
   end
 
   def test_satisfied_by_eh_blank
@@ -151,11 +147,7 @@ class TestGemRequirement < Gem::TestCase
     assert_satisfied_by "1.2", r
     refute_satisfied_by "1.3", r
 
-    assert_raise ArgumentError do
-      Gem::Deprecate.skip_during do
-        assert_satisfied_by nil, r
-      end
-    end
+    refute_satisfied_by nil, r
   end
 
   def test_satisfied_by_eh_equal
@@ -165,11 +157,7 @@ class TestGemRequirement < Gem::TestCase
     assert_satisfied_by "1.2", r
     refute_satisfied_by "1.3", r
 
-    assert_raise ArgumentError do
-      Gem::Deprecate.skip_during do
-        assert_satisfied_by nil, r
-      end
-    end
+    refute_satisfied_by nil, r
   end
 
   def test_satisfied_by_eh_gt
@@ -179,9 +167,7 @@ class TestGemRequirement < Gem::TestCase
     refute_satisfied_by "1.2", r
     assert_satisfied_by "1.3", r
 
-    assert_raise ArgumentError do
-      r.satisfied_by? nil
-    end
+    refute_satisfied_by nil, r
   end
 
   def test_satisfied_by_eh_gte
diff --git a/test/rubygems/test_gem_specification.rb b/test/rubygems/test_gem_specification.rb
index 05138e570e..e8c2c0eb47 100644
--- a/test/rubygems/test_gem_specification.rb
+++ b/test/rubygems/test_gem_specification.rb
@@ -1247,12 +1247,37 @@ dependencies: []
   end
 
   def test_initialize_nil_version
-    expected = "nil versions are discouraged and will be deprecated in Rubygems 4\n"
-    actual_stdout, actual_stderr = capture_output do
-      Gem::Specification.new.version = nil
+    spec = Gem::Specification.new
+    spec.name = "test-name"
+
+    assert_nil spec.version
+    spec.version = nil
+    assert_nil spec.version
+
+    spec.summary = "test gem"
+    spec.authors = ["test author"]
+    e = assert_raise Gem::InvalidSpecificationException do
+      spec.validate
     end
-    assert_empty actual_stdout
-    assert_equal(expected, actual_stderr)
+    assert_match("missing value for attribute version", e.message)
+  end
+
+  def test_set_version_to_nil_after_setting_version
+    spec = Gem::Specification.new
+    spec.name = "test-name"
+
+    assert_nil spec.version
+    spec.version = "1.0.0"
+    assert_equal "1.0.0", spec.version.to_s
+    spec.version = nil
+    assert_nil spec.version
+
+    spec.summary = "test gem"
+    spec.authors = ["test author"]
+    e = assert_raise Gem::InvalidSpecificationException do
+      spec.validate
+    end
+    assert_match("missing value for attribute version", e.message)
   end
 
   def test__dump
diff --git a/test/rubygems/test_gem_version.rb b/test/rubygems/test_gem_version.rb
index cf771bc5a1..1d963daa65 100644
--- a/test/rubygems/test_gem_version.rb
+++ b/test/rubygems/test_gem_version.rb
@@ -7,6 +7,11 @@ class TestGemVersion < Gem::TestCase
   class V < ::Gem::Version
   end
 
+  def test_nil_is_zero
+    zero = Gem::Version.create nil
+    assert_equal Gem::Version.create(0), zero
+  end
+
   def test_bump
     assert_bumped_version_equal "5.3", "5.2.4"
   end
@@ -35,13 +40,6 @@ class TestGemVersion < Gem::TestCase
 
     assert_same real, Gem::Version.create(real)
 
-    expected = "nil versions are discouraged and will be deprecated in Rubygems 4\n"
-    actual_stdout, actual_stderr = capture_output do
-      assert_nil Gem::Version.create(nil)
-    end
-    assert_empty actual_stdout
-    assert_equal(expected, actual_stderr)
-
     assert_equal v("5.1"), Gem::Version.create("5.1")
 
     ver = "1.1"
@@ -51,13 +49,7 @@ class TestGemVersion < Gem::TestCase
   def test_class_correct
     assert_equal true,  Gem::Version.correct?("5.1")
     assert_equal false, Gem::Version.correct?("an incorrect version")
-
-    expected = "nil versions are discouraged and will be deprecated in Rubygems 4\n"
-    actual_stdout, actual_stderr = capture_output do
-      Gem::Version.correct?(nil)
-    end
-    assert_empty actual_stdout
-    assert_equal(expected, actual_stderr)
+    assert_equal true, Gem::Version.correct?(nil)
   end
 
   def test_class_new_subclass