Add base error class to new gems.

Closes #6260.

lib/bundler/cli.rb

@@ -515,6 +515,8 @@ def viz
     method_option :mit, :type => :boolean, :desc => "Generate an MIT license file. Set a default with `bundle config gem.mit true`."
     method_option :test, :type => :string, :lazy_default => "rspec", :aliases => "-t", :banner => "rspec",
                          :desc => "Generate a test directory for your library, either rspec or minitest. Set a default with `bundle config gem.test rspec`."
+    method_option :error_class, :type => :string, :default => "StandardError", :aliases => "-e",
+                                :desc => "Generate a base error class for your library."
     def gem(name)
     end
 

lib/bundler/cli/gem.rb

@@ -28,6 +28,7 @@ def initialize(options, gem_name, thor)
       @target = SharedHelpers.pwd.join(gem_name)
 
       validate_ext_name if options[:ext]
+      validate_error_class if options[:error_class]
     end
 
     def run
@@ -56,6 +57,7 @@ def run
         :test             => options[:test],
         :ext              => options[:ext],
         :exe              => options[:exe],
+        :error_class      => options[:error_class],
         :bundler_version  => bundler_dependency_version,
         :github_username  => github_username.empty? ? "[USERNAME]" : github_username
       }
@@ -242,6 +244,18 @@ def ensure_safe_gem_name(name, constant_array)
       exit 1
     end
 
+    def validate_error_class
+      error_class = options[:error_class]
+
+      if (error = Object.const_get(error_class)) && !(error <= Exception) # rubocop:disable Style/InverseMethods
+        Bundler.ui.error "Invalid error class #{error_class}. Please use a class inheriting from Exception."
+        exit 1
+      end
+    rescue NameError
+      Bundler.ui.error "Invalid class name #{error_class} for error class. Please provide an Exception subclass."
+      exit 1
+    end
+
     def open_editor(editor, file)
       thor.run(%(#{editor} "#{file}"))
     end

lib/bundler/templates/newgem/lib/newgem.rb.tt

@@ -6,6 +6,11 @@ require "<%= config[:namespaced_path] %>/<%= config[:underscored_name] %>"
 <%- config[:constant_array].each_with_index do |c, i| -%>
 <%= "  " * i %>module <%= c %>
 <%- end -%>
+<%- if config[:error_class] -%>
+<%= "  " * config[:constant_array].size %>class Error < <%= config[:error_class] %>
+<%= "  " * config[:constant_array].size %>  # Base class for your errors
+<%= "  " * config[:constant_array].size %>end
+<%- end -%>
 <%= "  " * config[:constant_array].size %># Your code goes here...
 <%- (config[:constant_array].size-1).downto(0) do |i| -%>
 <%= "  " * i %>end

spec/commands/newgem_spec.rb

@@ -310,6 +310,10 @@ def create_temporary_dir(dir)
       expect(bundled_app("test_gem/lib/test_gem.rb").read).to match(%r{require "test_gem/version"})
     end
 
+    it "creates a base error class" do
+      expect(bundled_app("test_gem/lib/test_gem.rb").read).to include("class Error < StandardError")
+    end
+
     it "runs rake without problems" do
       system_gems ["rake-10.0.2"]
 
@@ -550,6 +554,38 @@ def create_temporary_dir(dir)
     end
   end
 
+  context "--error-class flag set" do
+    context "with valid error class name" do
+      it "generates a gem skeleton with error subclassing given base class" do
+        execute_bundle_gem("test_gem", "--error-class RuntimeError")
+        expect(bundled_app("test_gem/lib/test_gem.rb").read).to include("< RuntimeError")
+      end
+    end
+
+    context "with non-error class name" do
+      it "fails to generate a gem skeleton" do
+        expect do
+          execute_bundle_gem("test_gem", "--error-class Enumerable")
+        end.to raise_error(RuntimeError, /Invalid error class/)
+      end
+    end
+
+    context "with invalid class name" do
+      it "fails to generate a gem skeleton" do
+        expect do
+          execute_bundle_gem("test_gem", "--error-class qpwoeiryt")
+        end.to raise_error(RuntimeError, /Invalid class name/)
+      end
+    end
+  end
+
+  context "--no-error-class flag set" do
+    it "generates a gem skeleton without error subclass" do
+      execute_bundle_gem("test_gem", "--no-error-class")
+      expect(bundled_app("test_gem/lib/test_gem.rb").read).to_not include("class Error")
+    end
+  end
+
   context "gem naming with dashed" do
     let(:gem_name) { "test-gem" }