Configuration validation

Validate the Kamal configuration giving useful warning on errors.
Each section of the configuration has its own config class and a YAML
file containing documented example configuration.

You can run `kamal docs` to see the example configuration, and
`kamal docs <section>` to see the example configuration for a specific
section.

The validation matches the configuration to the example configuration
checking that there are no unknown keys and that the values are of
matching types.

Where there is more complex validation - e.g for envs and servers, we
have custom validators that implement those rules.

Additonally the configuration examples are used to generate the
configuration documentation in the kamal-site repo.

You generate them by running:

```
bundle exec bin/docs <kamal-site-checkout>
```

test/cli/main_test.rb

@@ -372,19 +372,6 @@ class CliMainTest < CliTestCase
     end
   end
 
-  test "config with aliases" do
-    run_command("config", config_file: "deploy_with_aliases").tap do |output|
-      config = YAML.load(output)
-
-      assert_equal [ "web", "web_tokyo", "workers", "workers_tokyo" ], config[:roles]
-      assert_equal [ "1.1.1.1", "1.1.1.2", "1.1.1.3", "1.1.1.4" ], config[:hosts]
-      assert_equal "999", config[:version]
-      assert_equal "registry.digitalocean.com/dhh/app", config[:repository]
-      assert_equal "registry.digitalocean.com/dhh/app:999", config[:absolute_image]
-      assert_equal "app-999", config[:service_with_version]
-    end
-  end
-
   test "init" do
     Pathname.any_instance.expects(:exist?).returns(false).times(3)
     Pathname.any_instance.stubs(:mkpath)
@@ -437,11 +424,10 @@ class CliMainTest < CliTestCase
   end
 
   test "envify" do
-    Pathname.any_instance.expects(:exist?).returns(true).times(3)
-    File.expects(:read).with(".env.erb").returns("HELLO=<%= 'world' %>")
-    File.expects(:write).with(".env", "HELLO=world", perm: 0600)
-
-    run_command("envify")
+    with_test_dot_env_erb(contents: "HELLO=<%= 'world' %>") do
+      run_command("envify")
+      assert_equal("HELLO=world", File.read(".env"))
+    end
   end
 
   test "envify with blank line trimming" do
@@ -452,19 +438,17 @@ class CliMainTest < CliTestCase
       <% end  -%>
     EOF
 
-    Pathname.any_instance.expects(:exist?).returns(true).times(3)
-    File.expects(:read).with(".env.erb").returns(file.strip)
-    File.expects(:write).with(".env", "HELLO=world\nKEY=value\n", perm: 0600)
-
-    run_command("envify")
+    with_test_dot_env_erb(contents: file) do
+      run_command("envify")
+      assert_equal("HELLO=world\nKEY=value\n", File.read(".env"))
+    end
   end
 
   test "envify with destination" do
-    Pathname.any_instance.expects(:exist?).returns(true).times(4)
-    File.expects(:read).with(".env.world.erb").returns("HELLO=<%= 'world' %>")
-    File.expects(:write).with(".env.world", "HELLO=world", perm: 0600)
-
-    run_command("envify", "-d", "world", config_file: "deploy_for_dest")
+    with_test_dot_env_erb(contents: "HELLO=<%= 'world' %>", file: ".env.world.erb") do
+      run_command("envify", "-d", "world", config_file: "deploy_for_dest")
+      assert_equal "HELLO=world", File.read(".env.world")
+    end
   end
 
   test "envify with skip_push" do
@@ -500,6 +484,24 @@ class CliMainTest < CliTestCase
     end
   end
 
+  test "docs" do
+    run_command("docs").tap do |output|
+      assert_match "# Kamal Configuration", output
+    end
+  end
+
+  test "docs subsection" do
+    run_command("docs", "accessory").tap do |output|
+      assert_match "# Accessories", output
+    end
+  end
+
+  test "docs unknown" do
+    run_command("docs", "foo").tap do |output|
+      assert_match "No documentation found for foo", output
+    end
+  end
+
   test "version" do
     version = stdouted { Kamal::Cli::Main.new.version }
     assert_equal Kamal::VERSION, version
@@ -509,4 +511,17 @@ class CliMainTest < CliTestCase
     def run_command(*command, config_file: "deploy_simple")
       stdouted { Kamal::Cli::Main.start([ *command, "-c", "test/fixtures/#{config_file}.yml" ]) }
     end
+
+    def with_test_dot_env_erb(contents:, file: ".env.erb")
+      Dir.mktmpdir do |dir|
+        fixtures_dup = File.join(dir, "test")
+        FileUtils.mkdir_p(fixtures_dup)
+        FileUtils.cp_r("test/fixtures/", fixtures_dup)
+
+        Dir.chdir(dir) do
+          File.write(file, contents)
+          yield
+        end
+      end
+    end
 end