Add gitlab: Git source shorthand

This new shorthand, similar to the existing `github:` shorthand, adds
support for Gitlab repositories with a notable difference. Gitlab
projects may be organized into projects and subprojects. An example
Ruby gem exists at:

https://gitlab.com/gitlab-org/analytics-section/product-analytics/gl-application-sdk-rb

With the new shorthand, a user may install this gem from its repository
by adding:

```ruby
gem "gitlab-sdk", gitlab: "gitlab-org/analytics-section/product-analytics/gl-application-sdk-rb"
```

As with the `github:` shorthand, a supplied string with no `/` will be
interpreted as `example/example`.

Also in keeping with the utility of the `github:` shorthand, the new
`gitlab:` shorthand also supports Merge Request URLs.

```ruby
gem "gitlab-sdk", gitlab: "https://gitlab.com/gitlab-org/analytics-section/product-analytics/gl-application-sdk-rb/-/merge_requests/27"
```

The `gitlab:` gem source shortcut is modeled on the existing `github:`
shortcut, so the new specs mimic the existing examples.

bundler/lib/bundler/dsl.rb

@@ -19,6 +19,7 @@ def self.evaluate(gemfile, lockfile, unlock)
                     platform platforms type source install_if gemfile force_ruby_platform].freeze
 
     GITHUB_PULL_REQUEST_URL = %r{\Ahttps://github\.com/([A-Za-z0-9_\-\.]+/[A-Za-z0-9_\-\.]+)/pull/(\d+)\z}
+    GITLAB_MERGE_REQUEST_URL = %r{\Ahttps://gitlab\.com/([A-Za-z0-9_\-\./]+)/-/merge_requests/(\d+)\z}
 
     attr_reader :gemspecs, :gemfile
     attr_accessor :dependencies
@@ -308,6 +309,20 @@ def add_git_sources
         repo_name ||= user_name
         "https://#{user_name}@bitbucket.org/#{user_name}/#{repo_name}.git"
       end
+
+      git_source(:gitlab) do |repo_name|
+        if repo_name =~ GITLAB_MERGE_REQUEST_URL
+          {
+            "git" => "https://gitlab.com/#{$1}.git",
+            "branch" => nil,
+            "ref" => "refs/merge-requests/#{$2}/head",
+            "tag" => nil
+          }
+        else
+          repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
+          "https://gitlab.com/#{repo_name}.git"
+        end
+      end
     end
 
     def with_source(source)

bundler/spec/bundler/dsl_spec.rb

@@ -31,6 +31,13 @@
       expect(subject.dependencies.first.source.uri).to eq(github_uri)
       expect(subject.dependencies.first.source.ref).to eq("refs/pull/5/head")
     end
+
+    it "converts :gitlab PR to URI using https" do
+      subject.gem("sparks", gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5")
+      gitlab_uri = "https://gitlab.com/indirect/sparks.git"
+      expect(subject.dependencies.first.source.uri).to eq(gitlab_uri)
+      expect(subject.dependencies.first.source.ref).to eq("refs/merge-requests/5/head")
+    end
 
     it "rejects :github PR URI with a branch, ref or tag" do
       expect do
@@ -54,6 +61,29 @@
         %(The :tag option can't be used with `github: "https://github.com/indirect/sparks/pull/5"`),
       )
     end
+
+    it "rejects :gitlab PR URI with a branch, ref or tag" do
+      expect do
+        subject.gem("sparks", gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5", branch: "foo")
+      end.to raise_error(
+        Bundler::GemfileError,
+        %(The :branch option can't be used with `gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5"`),
+      )
+
+      expect do
+        subject.gem("sparks", gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5", ref: "foo")
+      end.to raise_error(
+        Bundler::GemfileError,
+        %(The :ref option can't be used with `gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5"`),
+      )
+
+      expect do
+        subject.gem("sparks", gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5", tag: "foo")
+      end.to raise_error(
+        Bundler::GemfileError,
+        %(The :tag option can't be used with `gitlab: "https://gitlab.com/indirect/sparks/-/merge_requests/5"`),
+      )
+    end
 
     it "rejects :github with :git" do
       expect do
@@ -63,6 +93,15 @@
         %(The :git option can't be used with `github: "indirect/sparks"`),
       )
     end
+
+    it "rejects :gitlab with :git" do
+      expect do
+        subject.gem("sparks", gitlab: "indirect/sparks", git: "https://gitlab.com/indirect/sparks.git")
+      end.to raise_error(
+        Bundler::GemfileError,
+        %(The :git option can't be used with `gitlab: "indirect/sparks"`),
+      )
+    end
 
     context "default hosts", bundler: "< 3" do
       it "converts :github to URI using https" do
@@ -76,6 +115,18 @@
         github_uri = "https://github.com/rails/rails.git"
         expect(subject.dependencies.first.source.uri).to eq(github_uri)
       end
+
+      it "converts :gitlab to URI using https" do
+        subject.gem("sparks", gitlab: "indirect/sparks")
+        gitlab_uri = "https://gitlab.com/indirect/sparks.git"
+        expect(subject.dependencies.first.source.uri).to eq(gitlab_uri)
+      end
+
+      it "converts :gitlab shortcut to URI using https" do
+        subject.gem("sparks", gitlab: "rails")
+        gitlab_uri = "https://gitlab.com/rails/rails.git"
+        expect(subject.dependencies.first.source.uri).to eq(gitlab_uri)
+      end
 
       it "converts numeric :gist to :git" do
         subject.gem("not-really-a-gem", gist: 2_859_988)
@@ -103,8 +154,8 @@
     end
 
     context "default git sources" do
-      it "has bitbucket, gist, and github" do
-        expect(subject.instance_variable_get(:@git_sources).keys.sort).to eq(%w[bitbucket gist github])
+      it "has bitbucket, gist, github, and gitlab" do
+        expect(subject.instance_variable_get(:@git_sources).keys.sort).to eq(%w[bitbucket gist github gitlab])
       end
     end
   end