Implement review comments from @dbalexandre.

- Don't define "allowed environment variables" in two places.
- Dispatch to different arities of `Popen.open` without an if/else block.
- Use `described_class` instead of explicitly stating the class name within a
- spec.
- Remove `git_environment_variables_validator_spec` and keep the validation inline.

app/validators/git_environment_variables_validator.rb

-class GitEnvironmentVariablesValidator < ActiveModel::EachValidator
-  def validate_each(record, attribute, env)
-    variables_to_validate = %w(GIT_OBJECT_DIRECTORY GIT_ALTERNATE_OBJECT_DIRECTORIES)
-
-    variables_to_validate.each do |variable_name|
-      variable_value = env[variable_name]
-
-      if variable_value.present? && !(variable_value =~ /^#{record.project.repository.path_to_repo}/)
-        record.errors.add(attribute, "The #{variable_name} variable must start with the project repo path")
-      end
-    end
-  end
-end

lib/gitlab/git/rev_list.rb

@@ -3,12 +3,10 @@
 module Gitlab
   module Git
     class RevList
-      include ActiveModel::Validations
-
-      validates :env, git_environment_variables: true
-
       attr_reader :project, :env
 
+      ALLOWED_VARIABLES = %w(GIT_OBJECT_DIRECTORY GIT_ALTERNATE_OBJECT_DIRECTORIES).freeze
+
       def initialize(oldrev, newrev, project:, env: nil)
         @project = project
         @env = env.presence || {}
@@ -21,17 +19,21 @@ module Gitlab
       end
 
       def execute
-        if self.valid?
-          Gitlab::Popen.popen(@args, nil, @env.slice(*allowed_environment_variables))
-        else
-          Gitlab::Popen.popen(@args)
+        Gitlab::Popen.popen(@args, nil, parse_environment_variables)
+      end
+
+      def valid?
+        env.slice(*ALLOWED_VARIABLES).all? do |(name, value)|
+          value =~ /^#{project.repository.path_to_repo}/
         end
       end
 
       private
 
-      def allowed_environment_variables
-        %w(GIT_ALTERNATE_OBJECT_DIRECTORIES GIT_OBJECT_DIRECTORY)
+      def parse_environment_variables
+        return {} unless valid?
+
+        env.slice(*ALLOWED_VARIABLES)
       end
     end
   end

spec/lib/gitlab/git/rev_list_spec.rb

 require 'spec_helper'
-require 'validators/git_environment_variables_validator_spec'
 
 describe Gitlab::Git::RevList, lib: true do
   let(:project) { create(:project) }
 
   context "validations" do
-    it_behaves_like(
-      "validated git environment variables",
-      ->(env, project) { Gitlab::Git::RevList.new('oldrev', 'newrev', project: project, env: env) }
-    )
+    context "GIT_OBJECT_DIRECTORY" do
+      it "accepts values starting with the project repo path" do
+        env = { "GIT_OBJECT_DIRECTORY" => "#{project.repository.path_to_repo}/objects" }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).to be_valid
+      end
+
+      it "rejects values starting not with the project repo path" do
+        env = { "GIT_OBJECT_DIRECTORY" => "/some/other/path" }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).not_to be_valid
+      end
+
+      it "rejects values containing the project repo path but not starting with it" do
+        env = { "GIT_OBJECT_DIRECTORY" => "/some/other/path/#{project.repository.path_to_repo}" }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).not_to be_valid
+      end
+    end
+
+    context "GIT_ALTERNATE_OBJECT_DIRECTORIES" do
+      it "accepts values starting with the project repo path" do
+        env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => project.repository.path_to_repo }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).to be_valid
+      end
+
+      it "rejects values starting not with the project repo path" do
+        env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => "/some/other/path" }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).not_to be_valid
+      end
+
+      it "rejects values containing the project repo path but not starting with it" do
+        env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => "/some/other/path/#{project.repository.path_to_repo}" }
+        rev_list = described_class.new('oldrev', 'newrev', project: project, env: env)
+
+        expect(rev_list).not_to be_valid
+      end
+    end
   end
 
   context "#execute" do

spec/validators/git_environment_variables_validator_spec.rb

-require 'spec_helper'
-
-shared_examples_for "validated git environment variables" do |record_fn| 
-  subject { GitEnvironmentVariablesValidator.new(attributes: ['env']) }
-  let(:project) { create(:project) }
-
-  context "GIT_OBJECT_DIRECTORY" do
-    it "accepts values starting with the project repo path" do
-      env = { "GIT_OBJECT_DIRECTORY" => "#{project.repository.path_to_repo}/objects" }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_valid, "expected #{project.repository.path_to_repo}"
-    end
-
-    it "rejects values starting not with the project repo path" do
-      env = { "GIT_OBJECT_DIRECTORY" => "/some/other/path" }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_invalid
-    end
-
-    it "rejects values containing the project repo path but not starting with it" do
-      env = { "GIT_OBJECT_DIRECTORY" => "/some/other/path/#{project.repository.path_to_repo}" }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_invalid
-    end
-  end
-
-  context "GIT_ALTERNATE_OBJECT_DIRECTORIES" do
-    it "accepts values starting with the project repo path" do
-      env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => project.repository.path_to_repo }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_valid, "expected #{project.repository.path_to_repo}"
-    end
-
-    it "rejects values starting not with the project repo path" do
-      env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => "/some/other/path" }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_invalid
-    end
-
-    it "rejects values containing the project repo path but not starting with it" do
-      env = { "GIT_ALTERNATE_OBJECT_DIRECTORIES" => "/some/other/path/#{project.repository.path_to_repo}" }
-      record = record_fn[env, project]
-
-      subject.validate_each(record, 'env', env)
-
-      expect(record).to be_invalid
-    end
-  end
-end