feat: add flag to print resolved config

cmd/yamlfmt/flags.go

@@ -34,6 +34,7 @@ operation without performing it.`)
 	flagConf              *string = flag.String("conf", "", "Read yamlfmt config from this path")
 	flagGlobalConf        *bool   = flag.Bool("global_conf", false, fmt.Sprintf("Use global yamlfmt config from %s", globalConfFlagVar()))
 	flagDisableGlobalConf *bool   = flag.Bool("no_global_conf", false, fmt.Sprintf("Disabled usage of global yamlfmt config from %s", globalConfFlagVar()))
+	flagResolvedConf      *bool   = flag.Bool("resolved_conf", false, "Print resolved config")
 	flagDoublestar        *bool   = flag.Bool("dstar", false, "Use doublestar globs for include and exclude")
 	flagQuiet             *bool   = flag.Bool("quiet", false, "Print minimal output to stdout")
 	flagContinueOnError   *bool   = flag.Bool("continue_on_error", false, "Continue to format files that didn't fail instead of exiting with code 1.")
@@ -97,6 +98,9 @@ func getOperationFromFlag() yamlfmt.Operation {
 	if *flagDry {
 		return yamlfmt.OperationDry
 	}
+	if *flagResolvedConf {
+		return yamlfmt.OperationPrintConfig
+	}
 	return yamlfmt.OperationFormat
 }
 

command/command.go

@@ -23,30 +23,61 @@ import (
 
 	"github.com/google/yamlfmt"
 	"github.com/google/yamlfmt/engine"
+
+	"github.com/braydonk/yaml"
 )
 
 type FormatterConfig struct {
 	Type              string         `mapstructure:"type"`
 	FormatterSettings map[string]any `mapstructure:",remain"`
 }
 
+func (f *FormatterConfig) flatten() map[string]any {
+	flat := make(map[string]any, len(f.FormatterSettings)+1)
+	if f.Type == "" {
+		flat["type"] = yamlfmt.BasicFormatterType
+	} else {
+		flat["type"] = f.Type
+	}
+
+	for k, v := range f.FormatterSettings {
+		flat[k] = v
+	}
+
+	return flat
+}
+
 // NewFormatterConfig returns an empty formatter config with all fields initialized.
 func NewFormatterConfig() *FormatterConfig {
 	return &FormatterConfig{FormatterSettings: make(map[string]any)}
 }
 
 type Config struct {
-	Extensions        []string                  `mapstructure:"extensions"`
-	Include           []string                  `mapstructure:"include"`
-	Exclude           []string                  `mapstructure:"exclude"`
-	RegexExclude      []string                  `mapstructure:"regex_exclude"`
-	FormatterConfig   *FormatterConfig          `mapstructure:"formatter,omitempty"`
-	Doublestar        bool                      `mapstructure:"doublestar"`
-	ContinueOnError   bool                      `mapstructure:"continue_on_error"`
-	LineEnding        yamlfmt.LineBreakStyle    `mapstructure:"line_ending"`
-	GitignoreExcludes bool                      `mapstructure:"gitignore_excludes"`
-	GitignorePath     string                    `mapstructure:"gitignore_path"`
-	OutputFormat      engine.EngineOutputFormat `mapstructure:"output_format"`
+	Extensions        []string                  `mapstructure:"extensions" yaml:"extensions"`
+	Include           []string                  `mapstructure:"include" yaml:"include"`
+	Exclude           []string                  `mapstructure:"exclude" yaml:"exclude"`
+	RegexExclude      []string                  `mapstructure:"regex_exclude" yaml:"regex_exclude"`
+	FormatterConfig   *FormatterConfig          `mapstructure:"formatter,omitempty" yaml:"-"`
+	Doublestar        bool                      `mapstructure:"doublestar" yaml:"doublestar"`
+	ContinueOnError   bool                      `mapstructure:"continue_on_error" yaml:"continue_on_error"`
+	LineEnding        yamlfmt.LineBreakStyle    `mapstructure:"line_ending" yaml:"line_ending"`
+	GitignoreExcludes bool                      `mapstructure:"gitignore_excludes" yaml:"gitignore_excludes"`
+	GitignorePath     string                    `mapstructure:"gitignore_path" yaml:"gitignore_path"`
+	OutputFormat      engine.EngineOutputFormat `mapstructure:"output_format" yaml:"output_format"`
+}
+
+func (c *Config) Marshal() ([]byte, error) {
+	conf, err := yaml.Marshal(c)
+	if err != nil {
+		return []byte{}, err
+	}
+	formatterConf, err := yaml.Marshal(struct {
+		Formatter map[string]any `yaml:"formatter"`
+	}{Formatter: c.FormatterConfig.flatten()})
+	if err != nil {
+		return []byte{}, err
+	}
+	return append(conf, formatterConf...), nil
 }
 
 type Command struct {
@@ -159,6 +190,16 @@ func (c *Command) Run() error {
 			return err
 		}
 		fmt.Print(string(out))
+	case yamlfmt.OperationPrintConfig:
+		conf, err := c.Config.Marshal()
+		if err != nil {
+			return err
+		}
+		formatted, err := formatter.Format(conf)
+		if err != nil {
+			return err
+		}
+		fmt.Println(string(formatted))
 	}
 
 	return nil

docs/command-usage.md

@@ -59,14 +59,15 @@ All flags must be specified **before** any path arguments.
 
 These flags adjust the command's mode of operation. All of these flags are booleans.
 
-| Name          | Flag       | Example                     | Description                                               |
-| :------------ | :--------- | :-------------------------- | :-------------------------------------------------------- |
-| Help          | `-help`    | `yamlfmt -help`             | Print the command usage information.                      |
-| Print Version | `-version` | `yamlfmt -version`          | Print the yamlfmt version.                                |
-| Dry Run       | `-dry`     | `yamlfmt -dry .`            | Use [Dry Run](#dry-run) mode                              |
-| Lint          | `-lint`    | `yamlfmt -lint .`           | Use [Lint](#lint) mode                                    |
-| Quiet Mode    | `-quiet`   | `yamlfmt -dry -quiet .`     | Use quiet mode. Only has effect in Dry Run or Lint modes. |
-| Read Stdin    | `-in`      | `cat x.yaml \| yamlfmt -in` | Read input from stdin and output result to stdout.        |
+| Name          | Flag             | Example                   | Description                                               |
+| :------------ | :--------------- | :------------------------ | :-------------------------------------------------------- |
+| Help          | `-help`          | `yamlfmt -help`           | Print the command usage information.                      |
+| Print Version | `-version`       | `yamlfmt -version`        | Print the yamlfmt version.                                |
+| Print Config  | `-resolved_conf` | `yamlfmt -resolved_conf`  | Print the merged configuration to use.                    |
+| Dry Run       | `-dry`           | `yamlfmt -dry .`          | Use [Dry Run](#dry-run) mode                              |
+| Lint          | `-lint`          | `yamlfmt -lint .`         | Use [Lint](#lint) mode                                    |
+| Quiet Mode    | `-quiet`         | `yamlfmt -dry -quiet .`   | Use quiet mode. Only has effect in Dry Run or Lint modes. |
+| Read Stdin    | `-in`            | `cat x.yaml \| yamlfmt -in` | Read input from stdin and output result to stdout.        |
 
 ### Configuration Flags
 

docs/config-file.md

@@ -26,6 +26,8 @@ If the flag `-global_conf` is passed, all other steps will be circumvented and t
 
 In the `-conf` flag, the config file can be named anything. As long as it's valid yaml, yamlfmt will read it as a config file. This can be useful for applying unique configs to different directories in a project. The automatic discovery paths do need to use one of the known names.
 
+In the `-resolved_conf` flag, merged config values will be printed.
+
 ## Command
 
 The command package defines the main command engine that `cmd/yamlfmt` uses. It uses the top level configuration that any run of the yamlfmt command will use.

engine.go

@@ -29,6 +29,7 @@ const (
 	OperationLint
 	OperationDry
 	OperationStdin
+	OperationPrintConfig
 )
 
 type Engine interface {

formatter.go

@@ -16,6 +16,8 @@ package yamlfmt
 
 import "fmt"
 
+const BasicFormatterType string = "basic"
+
 type Formatter interface {
 	Type() string
 	Format(yamlContent []byte) ([]byte, error)

formatters/basic/factory.go

@@ -22,7 +22,7 @@ import (
 type BasicFormatterFactory struct{}
 
 func (f *BasicFormatterFactory) Type() string {
-	return BasicFormatterType
+	return yamlfmt.BasicFormatterType
 }
 
 func (f *BasicFormatterFactory) NewFormatter(configData map[string]interface{}) (yamlfmt.Formatter, error) {

formatters/basic/formatter.go

@@ -23,8 +23,6 @@ import (
 	"github.com/google/yamlfmt"
 )
 
-const BasicFormatterType string = "basic"
-
 type BasicFormatter struct {
 	Config       *Config
 	Features     yamlfmt.FeatureList
@@ -34,7 +32,7 @@ type BasicFormatter struct {
 // yamlfmt.Formatter interface
 
 func (f *BasicFormatter) Type() string {
-	return BasicFormatterType
+	return yamlfmt.BasicFormatterType
 }
 
 func (f *BasicFormatter) Format(input []byte) ([]byte, error) {

integrationtest/command/command_test.go

@@ -100,3 +100,11 @@ func TestDryQuiet(t *testing.T) {
 		Update:  *updateFlag,
 	}.Run(t)
 }
+
+func TestResolvedConf(t *testing.T) {
+	TestCase{
+		Dir:     "resolved_conf",
+		Command: yamlfmtWithArgs("-resolved_conf -continue_on_error=true -formatter retain_line_breaks=true"),
+		Update:  *updateFlag,
+	}.Run(t)
+}

integrationtest/command/testdata/resolved_conf/after/a.yaml

@@ -0,0 +1,2 @@
+a:
+ b: 1

integrationtest/command/testdata/resolved_conf/before/a.yaml

@@ -0,0 +1,2 @@
+a:
+ b: 1

integrationtest/command/testdata/resolved_conf/stdout/stdout.txt

@@ -0,0 +1,17 @@
+extensions:
+  - yaml
+  - yml
+include: []
+exclude: []
+regex_exclude: []
+doublestar: false
+continue_on_error: true
+line_ending: lf
+gitignore_excludes: false
+gitignore_path: .gitignore
+output_format: default
+formatter:
+  line_ending: lf
+  retain_line_breaks: true
+  type: basic
+