[action]Adds action for obtaining remote repo default branch

fastlane/lib/fastlane/actions/git_remote_branch.rb

@@ -0,0 +1,57 @@
+module Fastlane
+  module Actions
+    class GitRemoteBranchAction < Action
+      def self.run(params)
+        Actions.git_remote_branch_name(params[:remote_name])
+      end
+
+      #####################################################
+      # @!group Documentation
+      #####################################################
+
+      def self.description
+        "Returns the name of the current git remote default branch"
+      end
+
+      def self.details
+        "If no default remote branch could be found, this action will return nil. This is a wrapper for the internal action Actions.git_default_remote_branch_name"
+      end
+
+      def self.available_options
+        [
+          FastlaneCore::ConfigItem.new(key: :remote_name,
+                                       env_name: "FL_REMOTE_REPOSITORY_NAME",
+                                       description: "The remote repository to check",
+                                       optional: true)
+        ]
+      end
+
+      def self.output
+        []
+      end
+
+      def self.authors
+        ["SeanMcNeil"]
+      end
+
+      def self.is_supported?(platform)
+        true
+      end
+
+      def self.example_code
+        [
+          'git_remote_branch # Query git for first available remote name',
+          'git_remote_branch(remote_name:"upstream") # Provide a remote name'
+        ]
+      end
+
+      def self.return_type
+        :string
+      end
+
+      def self.category
+        :source_control
+      end
+    end
+  end
+end

fastlane/lib/fastlane/helper/git_helper.rb

@@ -131,12 +131,24 @@ def self.git_branch
     # Returns the checked out git branch name or "HEAD" if you're in detached HEAD state
     def self.git_branch_name_using_HEAD
       # Rescues if not a git repo or no commits in a git repo
-      begin
-        Actions.sh("git rev-parse --abbrev-ref HEAD", log: false).chomp
-      rescue => err
-        UI.verbose("Error getting git branch: #{err.message}")
-        nil
+      Actions.sh("git rev-parse --abbrev-ref HEAD", log: false).chomp
+    rescue => err
+      UI.verbose("Error getting git branch: #{err.message}")
+      nil
+    end
+
+    # Returns the default git remote branch name
+    def self.git_remote_branch_name(remote_name)
+      # Rescues if not a git repo or no remote repo
+      if remote_name
+        Actions.sh("git remote show #{remote_name} | grep 'HEAD branch' | sed 's/.*: //'", log: false).chomp
+      else
+        # Query git for the current remote head
+        Actions.sh("variable=$(git remote) && git remote show $variable | grep 'HEAD branch' | sed 's/.*: //'", log: false).chomp
       end
+    rescue => err
+      UI.verbose("Error getting git default remote branch: #{err.message}")
+      nil
     end
 
     private_class_method

fastlane/spec/actions_specs/git_remote_branch_spec.rb

@@ -0,0 +1,83 @@
+describe Fastlane do
+  describe Fastlane::FastFile do
+    directory = "fl_spec_default_remote_branch"
+
+    describe "Git Remote Branch Action" do
+      it "generates the correct git command for retrieving default branch from remote" do
+        result = Fastlane::FastFile.new.parse("lane :test do
+            git_remote_branch
+          end").runner.execute(:test)
+
+        expect(result).to eq("variable=$(git remote) && git remote show $variable | grep 'HEAD branch' | sed 's/.*: //'")
+      end
+    end
+
+    describe "Git Remote Branch Action with optional remote name" do
+      it "generates the correct git command for retrieving default branch using provided remote name" do
+        result = Fastlane::FastFile.new.parse("lane :test do
+            git_remote_branch(remote_name:'upstream')
+          end").runner.execute(:test)
+
+        expect(result).to eq("git remote show upstream | grep 'HEAD branch' | sed 's/.*: //'")
+      end
+    end
+
+    context "runs the command in a directory with no git repo" do
+      it "Confirms that no default remote is found" do
+        test_directory_path = Dir.mktmpdir(directory)
+
+        Dir.chdir(test_directory_path) do
+          expect(Fastlane::Actions).to receive(:sh)
+            .with("variable=$(git remote) && git remote show $variable | grep 'HEAD branch' | sed 's/.*: //'", log: false)
+
+          result = Fastlane::FastFile.new.parse("lane :test do
+            git_remote_branch
+          end").runner.execute(:test)
+
+          expect(result).to be_nil
+        end
+      end
+    end
+
+    context "runs the command in a directory with no remote git repo" do
+      it "Confirms that no default remote is found" do
+        test_directory_path = Dir.mktmpdir(directory)
+
+        Dir.chdir(test_directory_path) do
+          `git init`
+
+          File.write('test_file', <<-TESTFILE)
+              'Hello'
+            TESTFILE
+          `git add .`
+          `git commit --message "Test file"`
+
+          expect(Fastlane::Actions).to receive(:sh)
+            .with("variable=$(git remote) && git remote show $variable | grep 'HEAD branch' | sed 's/.*: //'", log: false)
+
+          result = Fastlane::FastFile.new.parse("lane :test do
+            git_remote_branch
+          end").runner.execute(:test)
+
+          expect(result).to be_nil
+        end
+      end
+    end
+
+    context "runs the command with a remote git repo" do
+      it "Confirms that a default remote is found" do
+        allow(Fastlane::Actions).to receive(:sh)
+          .with("variable=$(git remote) && git remote show $variable | grep 'HEAD branch' | sed 's/.*: //'", log: false)
+          .and_return("main")
+        allow(Fastlane::Actions).to receive(:git_branch).and_return(nil)
+
+        result = Fastlane::FastFile.new.parse("lane :test do
+            git_remote_branch
+          end").runner.execute(:test)
+
+        expect(result).to eq("main")
+      end
+    end
+
+  end
+end