Add safe invocation CLI syntax

lib/rake/application.rb

@@ -179,6 +179,12 @@ def thread_pool             # :nodoc:
     # Invokes a task with arguments that are extracted from +task_string+
     def invoke_task(task_string) # :nodoc:
       name, args = parse_task_string(task_string)
+
+      if name.end_with?('?') && !lookup(name)
+        name = name[0..-2]
+        return unless lookup(name)
+      end
+
       t = self[name]
       t.invoke(*args)
     end

test/test_rake_application.rb

@@ -502,6 +502,29 @@ def test_good_run
     assert_equal "DEFAULT\n", out
   end
 
+  def test_safe_run
+    ran = false
+    existing_ran = false
+
+    @app.options.silent = true
+
+    @app.instance_eval do
+      intern(Rake::Task, "default").enhance { ran = true }
+      intern(Rake::Task, "existing?").enhance { existing_ran = true }
+    end
+
+    rakefile_default
+
+    out, err = capture_output do
+      @app.run %w[--rakelib="" default existing? missing?]
+    end
+
+    assert ran
+    assert existing_ran
+    assert_empty err
+    assert_equal "DEFAULT\n", out
+  end
+
   def test_display_task_run
     ran = false
     @app.last_description = "COMMENT"