enhance: improve config, comment out values in example file (#1145)

`config.example.yaml` now has every value commented out, as gitea's `app.example.ini` does, so it documents each option with its default instead of imposing it. Copying it no longer pins values the runner would otherwise pick, and a changed default reaches configs that never named the option.

`config init` writes the file to configure: a header comment and no option, so every option keeps its default. It refuses to overwrite an existing config without `--force`, and writes `config.yaml` in the working directory when `-c` is absent.

`config set`, `add` and `remove` keep such a file readable. Comments go back to the indentation they were written at, which the encoder drops for a comment block that has no key below it, and a file of only comments keeps its text instead of being emptied by the first edit.

Also rewrote the config docs sections for clarity.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1145
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

internal/app/cmd/config.go

@@ -26,6 +26,7 @@ func loadConfigCmd(configFile *string) *cobra.Command {
 	}
 
 	configCmd.AddCommand(loadGenerateConfigCmd("generate"))
+	configCmd.AddCommand(loadInitConfigCmd(configFile))
 
 	configCmd.AddCommand(&cobra.Command{
 		Use:   "get <key>",
@@ -73,10 +74,38 @@ func loadConfigCmd(configFile *string) *cobra.Command {
 	return configCmd
 }
 
+func loadInitConfigCmd(configFile *string) *cobra.Command {
+	var force bool
+	initCmd := &cobra.Command{
+		Use:   "init",
+		Short: "Write a minimal config file",
+		Long:  "Write a minimal config file, leaving every option at its default.\nWithout --config it writes config.yaml in the working directory.",
+		Args:  cobra.MaximumNArgs(0),
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			file, taken := *configFile, []string{*configFile}
+			if file == "" {
+				file, taken = defaultConfigFileNames[0], defaultConfigFileNames // any of them would shadow the new file
+			}
+			for _, name := range taken {
+				if _, err := os.Stat(name); err == nil && !force {
+					return fmt.Errorf("config file %q already exists, pass --force to overwrite it", name)
+				}
+			}
+			if err := config.WriteFile(file, []byte(config.Minimal)); err != nil {
+				return err
+			}
+			fmt.Fprintf(cmd.OutOrStdout(), "wrote config file %q\n", file)
+			return nil
+		},
+	}
+	initCmd.Flags().BoolVarP(&force, "force", "f", false, "overwrite an existing config file")
+	return initCmd
+}
+
 func loadGenerateConfigCmd(use string) *cobra.Command {
 	return &cobra.Command{
 		Use:   use,
-		Short: "Generate an example config file",
+		Short: "Print the example config, which documents every option",
 		Args:  cobra.MaximumNArgs(0),
 		Run: func(cmd *cobra.Command, _ []string) {
 			fmt.Fprintf(cmd.OutOrStdout(), "%s", config.Example)

internal/app/cmd/config_test.go

@@ -32,6 +32,30 @@ func TestConfigCmdGeneratePrintsTheExample(t *testing.T) {
 	assert.Equal(t, string(config.Example), out)
 }
 
+func TestConfigCmdInitWritesTheMinimalConfig(t *testing.T) {
+	dir := t.TempDir()
+	file := filepath.Join(dir, "config.yaml")
+
+	out, _, err := runConfigCmd(t, file, "init")
+	require.NoError(t, err)
+	assert.Contains(t, out, file)
+	content, err := os.ReadFile(file)
+	require.NoError(t, err)
+	assert.Equal(t, config.Minimal, string(content))
+
+	_, _, err = runConfigCmd(t, file, "init")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "--force")
+
+	_, _, err = runConfigCmd(t, file, "init", "--force")
+	require.NoError(t, err)
+
+	t.Chdir(t.TempDir())
+	_, _, err = runConfigCmd(t, "", "init")
+	require.NoError(t, err)
+	assert.FileExists(t, defaultConfigFileNames[0])
+}
+
 // The subcommands only wire arguments through, so one pass over all of them is enough.
 func TestConfigCmdEditsTheFile(t *testing.T) {
 	file := filepath.Join(t.TempDir(), "config.yaml")