fix: reject plugin names that cannot be a Ruby constant

lib/busser/command/plugin_create.rb

@@ -39,7 +39,22 @@ class PluginCreate < Busser::Thor::BaseGroup
       # Generates a new runner plugin project.
       #
       # @return [void]
+      # A plugin name becomes three things: a require path, a directory name and
+      # a Ruby constant. Only the last is fussy, and Thor's camel_case only
+      # folds underscores -- so "my-junit" produced `module My-junit`, which is
+      # not parseable Ruby. The generator ran to completion and wrote a project
+      # that could not be loaded at all.
+      NAME_PATTERN = /\A[a-z][a-z0-9_]*\z/
+
       def create
+        unless NAME_PATTERN.match?(name)
+          raise ::Thor::Error,
+            "'#{name}' is not a usable plugin name. A name becomes a Ruby " \
+            "constant, so it must start with a lowercase letter and contain " \
+            "only lowercase letters, digits and underscores. Try " \
+            "'#{suggested_name}'."
+        end
+
         self.class.source_root(Busser.source_root.join("templates", "plugin"))
 
         create_core_files
@@ -126,6 +141,12 @@ def create_template(erb, dest)
       end
 
       # @return [String] directory the new plugin is generated into
+      # @return [String] the given name reshaped into something usable, for the
+      #   error message
+      def suggested_name
+        name.to_s.downcase.gsub(/[^a-z0-9_]+/, "_").sub(/\A[^a-z]+/, "").squeeze("_")
+      end
+
       def target_dir
         File.join(Dir.pwd, "busser-#{name}")
       end

spec/busser/command/plugin_create_spec.rb

@@ -152,9 +152,51 @@ def dev_dependencies
     end
   end
 
-  def generate(license: "apachev2")
+  # A name becomes a Ruby constant, and Thor's camel_case only folds
+  # underscores. "my-junit" produced `module My-junit`, which does not parse --
+  # and the generator ran to completion anyway, leaving a project that could
+  # not be loaded at all.
+  describe "the plugin name" do
+
+    %w{demo junit my_junit j2 x}.each do |name|
+      it "accepts #{name.inspect}" do
+        generate(name: name)
+
+        _(Dir.exist?(File.join(@tmpdir, "busser-#{name}"))).must_equal true
+      end
+    end
+
+    {
+      "my-junit" => "a hyphen cannot appear in a constant",
+      "My_Junit" => "an uppercase start is not a plugin name",
+      "2fast" => "a constant cannot start with a digit",
+      "my junit" => "a space cannot appear in a constant or a path",
+      "" => "an empty name",
+      "../escaped" => "a path fragment",
+    }.each do |name, why|
+      it "rejects #{name.inspect} -- #{why}" do
+        err = _(proc { generate(name: name) }).must_raise ::Thor::Error
+
+        _(err.message).must_include "not a usable plugin name"
+      end
+    end
+
+    it "writes nothing when the name is rejected" do
+      _(proc { generate(name: "my-junit") }).must_raise ::Thor::Error
+
+      _(Dir.glob(File.join(@tmpdir, "*"))).must_be_empty
+    end
+
+    it "suggests a usable name" do
+      err = _(proc { generate(name: "my-junit") }).must_raise ::Thor::Error
+
+      _(err.message).must_include "'my_junit'"
+    end
+  end
+
+  def generate(license: "apachev2", name: "demo")
     command = Busser::Command::PluginCreate.new(
-      ["demo"], { "type" => "runner", "license" => license }
+      [name], { "type" => "runner", "license" => license }
     )
     command.stubs(:initialize_git)
     capture_stdout { command.create }