Updated after review

Apart from small fixes, this:
- adds deprecation check for command line arguments, and gives a
  warning if `--terragrunt-debug` is used;
- imports `logrus` under its own name to avoid confusion;

Related: gruntwork-io#432

cli/args.go

@@ -123,6 +123,16 @@ func parseTerragruntOptionsFromArgs(terragruntVersion string, args []string, wri
 
 	debug := parseBooleanArg(args, OPT_TERRAGRUNT_DEBUG, false)
 
+	// Those correspond to logrus levels
+	logLevel, err := parseStringArg(args, OPT_TERRAGRUNT_LOGLEVEL, options.DEFAULT_LOG_LEVEL)
+	if err != nil {
+		return nil, err
+	}
+
+	if debug {
+		logLevel = "debug"
+	}
+
 	opts, err := options.NewTerragruntOptions(filepath.ToSlash(terragruntConfigPath))
 	if err != nil {
 		return nil, err
@@ -143,7 +153,7 @@ func parseTerragruntOptionsFromArgs(terragruntVersion string, args []string, wri
 	opts.TerraformCommand = util.FirstArg(opts.TerraformCliArgs)
 	opts.WorkingDir = filepath.ToSlash(workingDir)
 	opts.DownloadDir = filepath.ToSlash(downloadDir)
-	opts.Logger = util.CreateLogEntryWithWriter(errWriter, "", debug)
+	opts.Logger = util.CreateLogEntryWithWriter(errWriter, "", logLevel)
 	opts.RunTerragrunt = RunTerragrunt
 	opts.Source = terraformSource
 	opts.SourceUpdate = sourceUpdate
@@ -169,7 +179,6 @@ func parseTerragruntOptionsFromArgs(terragruntVersion string, args []string, wri
 	opts.Parallelism = parallelism
 	opts.Check = parseBooleanArg(args, OPT_TERRAGRUNT_CHECK, os.Getenv("TERRAGRUNT_CHECK") == "true")
 	opts.HclFile = filepath.ToSlash(terragruntHclFilePath)
-	opts.Debug = debug
 	opts.AwsProviderPatchOverrides = awsProviderPatchOverrides
 
 	return opts, nil
@@ -290,11 +299,24 @@ func filterTerragruntArgs(args []string) []string {
 	return out
 }
 
+// isDeprecatedOption checks if provided option is deprecated, and returns its substitution
+// TODO: ideally, it would be better to make this return (string, err)
+func isDeprecatedOption(optionName string) string {
+	newOption, deprecated := DEPRECATED_ARGUMENTS[optionName]
+	if deprecated {
+		logger := util.CreateLogEntry("", "debug")
+		logger.Warnf("Command line option %s is deprecated, please consider using %s", optionName, newOption)
+		return newOption
+	}
+	return optionName
+}
+
 // Find a boolean argument (e.g. --foo) of the given name in the given list of arguments. If it's present, return true.
 // If it isn't, return defaultValue.
 func parseBooleanArg(args []string, argName string, defaultValue bool) bool {
 	for _, arg := range args {
 		if arg == fmt.Sprintf("--%s", argName) {
+			argName = isDeprecatedOption(argName)
 			return true
 		}
 	}
@@ -306,6 +328,7 @@ func parseBooleanArg(args []string, argName string, defaultValue bool) bool {
 func parseStringArg(args []string, argName string, defaultValue string) (string, error) {
 	for i, arg := range args {
 		if arg == fmt.Sprintf("--%s", argName) {
+			argName = isDeprecatedOption(argName)
 			if (i + 1) < len(args) {
 				return args[i+1], nil
 			} else {
@@ -321,6 +344,7 @@ func parseStringArg(args []string, argName string, defaultValue string) (string,
 func parseIntArg(args []string, argName string, envValue string, envProvided bool, defaultValue int) (int, error) {
 	for i, arg := range args {
 		if arg == fmt.Sprintf("--%s", argName) {
+			argName = isDeprecatedOption(argName)
 			if (i + 1) < len(args) {
 				return strconv.Atoi(args[i+1])
 			} else {
@@ -342,6 +366,7 @@ func parseMultiStringArg(args []string, argName string, defaultValue []string) (
 
 	for i, arg := range args {
 		if arg == fmt.Sprintf("--%s", argName) {
+			argName = isDeprecatedOption(argName)
 			if (i + 1) < len(args) {
 				stringArgs = append(stringArgs, args[i+1])
 			} else {

cli/cli_app.go

@@ -4,7 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	log "github.com/sirupsen/logrus"
+
 	"regexp"
 	"strings"
 	"time"
@@ -20,6 +20,7 @@ import (
 	"github.com/gruntwork-io/terragrunt/util"
 	"github.com/mattn/go-zglob"
 	"github.com/urfave/cli"
+	"github.com/sirupsen/logrus"
 )
 
 const OPT_TERRAGRUNT_CONFIG = "terragrunt-config"
@@ -44,6 +45,7 @@ const OPT_TERRAGRUNT_CHECK = "terragrunt-check"
 const OPT_TERRAGRUNT_HCLFMT_FILE = "terragrunt-hclfmt-file"
 const OPT_TERRAGRUNT_DEBUG = "terragrunt-debug"
 const OPT_TERRAGRUNT_OVERRIDE_ATTR = "terragrunt-override-attr"
+const OPT_TERRAGRUNT_LOGLEVEL="terragrunt-log-level"
 
 var ALL_TERRAGRUNT_BOOLEAN_OPTS = []string{
 	OPT_NON_INTERACTIVE,
@@ -127,6 +129,11 @@ var TERRAFORM_COMMANDS_THAT_DO_NOT_NEED_INIT = []string{
 	"graph-dependencies",
 }
 
+// DEPRECATED_ARGUMENTS is a map of deprecated arguments to the argument that replace them.
+var DEPRECATED_ARGUMENTS = map[string]string{
+	OPT_TERRAGRUNT_DEBUG: OPT_TERRAGRUNT_LOGLEVEL,
+}
+
 // Struct is output as JSON by 'terragrunt-info':
 type TerragruntInfoGroup struct {
 	ConfigPath       string
@@ -246,6 +253,8 @@ func runApp(cliContext *cli.Context) (finalErr error) {
 		return err
 	}
 
+	terragruntOptions.Logger.Debugf("Terragrunt Version: %s", cliContext.App.Version)
+
 	shell.PrepareConsole(terragruntOptions)
 
 	givenCommand := cliContext.Args().First()
@@ -601,7 +610,7 @@ func shouldCopyLockFile(args []string) bool {
 
 // Terraform 0.14 now generates a lock file when you run `terraform init`.
 // If any such file exists, this function will copy the lock file to the destination folder
-func copyLockFile(sourceFolder string, destinationFolder string, logger *log.Entry) error {
+func copyLockFile(sourceFolder string, destinationFolder string, logger *logrus.Entry) error {
 	sourceLockFilePath := util.JoinPath(sourceFolder, util.TerraformLockFile)
 	destinationLockFilePath := util.JoinPath(destinationFolder, util.TerraformLockFile)
 

cli/download_source.go

@@ -3,7 +3,6 @@ package cli
 import (
 	"fmt"
 	"io/ioutil"
-	log "github.com/sirupsen/logrus"
 	"net/url"
 	"os"
 	"regexp"
@@ -16,6 +15,7 @@ import (
 	"github.com/gruntwork-io/terragrunt/options"
 	"github.com/gruntwork-io/terragrunt/util"
 	"github.com/hashicorp/go-getter"
+	"github.com/sirupsen/logrus"
 	urlhelper "github.com/hashicorp/go-getter/helper/url"
 )
 
@@ -185,7 +185,7 @@ func writeVersionFile(terraformSource *TerraformSource) error {
 // 1. Always download source URLs pointing to local file paths.
 // 2. Only download source URLs pointing to remote paths if /T/W/H doesn't already exist or, if it does exist, if the
 //    version number in /T/W/H/.terragrunt-source-version doesn't match the current version.
-func ProcessTerraformSource(source string, downloadDir string, workingDir string, logger *log.Entry) (*TerraformSource, error) {
+func ProcessTerraformSource(source string, downloadDir string, workingDir string, logger *logrus.Entry) (*TerraformSource, error) {
 
 	canonicalWorkingDir, err := util.CanonicalPath(workingDir, "")
 	if err != nil {
@@ -279,7 +279,7 @@ func getForcedGetter(sourceUrl string) (string, string) {
 // (//), which typically represents the root of a modules repo (e.g. github.com/foo/infrastructure-modules) and the
 // path is everything after the double slash. If there is no double-slash in the URL, the root repo is the entire
 // sourceUrl and the path is an empty string.
-func splitSourceUrl(sourceUrl *url.URL, logger *log.Entry) (*url.URL, string, error) {
+func splitSourceUrl(sourceUrl *url.URL, logger *logrus.Entry) (*url.URL, string, error) {
 	pathSplitOnDoubleSlash := strings.SplitN(sourceUrl.Path, "//", 2)
 
 	if len(pathSplitOnDoubleSlash) > 1 {

codegen/generate.go

@@ -87,7 +87,7 @@ func WriteToFile(terragruntOptions *options.TerragruntOptions, basePath string,
 	if err := ioutil.WriteFile(targetPath, []byte(contentsToWrite), 0644); err != nil {
 		return errors.WithStackTrace(err)
 	}
-	terragruntOptions.Logger.Infof("Generated file %s.", targetPath)
+	terragruntOptions.Logger.Debugf("Generated file %s.", targetPath)
 	return nil
 }
 
@@ -114,7 +114,7 @@ func shouldContinueWithFileExists(terragruntOptions *options.TerragruntOptions,
 			return false, err
 		}
 		if !wasGenerated {
-			terragruntOptions.Logger.Debugf("ERROR: The file path %s already exists and was not generated by terragrunt.", path)
+			terragruntOptions.Logger.Errorf("ERROR: The file path %s already exists and was not generated by terragrunt.", path)
 			return false, errors.WithStackTrace(GenerateFileExistsError{path: path})
 		}
 		// Since file was generated by terragrunt, continue.

config/config_helpers.go

@@ -210,9 +210,9 @@ func runCommand(args []string, include *IncludeConfig, terragruntOptions *option
 	}
 
 	if suppressOutput {
-		terragruntOptions.Logger.Infof("run_cmd output: [REDACTED]")
+		terragruntOptions.Logger.Debugf("run_cmd output: [REDACTED]")
 	} else {
-		terragruntOptions.Logger.Infof("run_cmd output: [%s]", cmdOutput.Stdout)
+		terragruntOptions.Logger.Debugf("run_cmd output: [%s]", cmdOutput.Stdout)
 	}
 
 	return cmdOutput.Stdout, nil

config/config_test.go

@@ -376,7 +376,7 @@ include {
 	opts := options.TerragruntOptions{
 		TerragruntConfigPath: "../test/fixture-parent-folders/terragrunt-in-root/child/sub-child/sub-sub-child/" + DefaultTerragruntConfigPath,
 		NonInteractive:       true,
-		Logger:               util.CreateLogEntry("", false),
+		Logger:               util.CreateLogEntry("", "warn"),
 	}
 
 	terragruntConfig, err := ParseConfigString(config, &opts, nil, opts.TerragruntConfigPath)
@@ -1251,7 +1251,7 @@ terraform {
 		TerragruntConfigPath: "../test/fixture-parent-folders/terragrunt-in-root/child/" + DefaultTerragruntConfigPath,
 		NonInteractive:       true,
 		MaxFoldersToCheck:    5,
-		Logger:             util.CreateLogEntry("", false),
+		Logger:             util.CreateLogEntry("", "warn"),
 	}
 
 	terragruntConfig, err := ParseConfigString(config, &opts, nil, DefaultTerragruntConfigPath)

config/locals.go

@@ -64,7 +64,7 @@ func evaluateLocalsBlock(
 
 	locals, diags := decodeLocalsBlock(localsBlock)
 	if diags.HasErrors() {
-		terragruntOptions.Logger.Debugf("Encountered error while decoding locals block into name expression pairs.")
+		terragruntOptions.Logger.Errorf("Encountered error while decoding locals block into name expression pairs.")
 		diagsWriter.WriteDiagnostics(diags)
 		return nil, errors.WithStackTrace(diags)
 	}
@@ -90,15 +90,15 @@ func evaluateLocalsBlock(
 			diagsWriter,
 		)
 		if err != nil {
-			terragruntOptions.Logger.Debugf("Encountered error while evaluating locals.")
+			terragruntOptions.Logger.Errorf("Encountered error while evaluating locals.")
 			return nil, err
 		}
 	}
 	if len(locals) > 0 {
 		// This is an error because we couldn't evaluate all locals
-		terragruntOptions.Logger.Debugf("Not all locals could be evaluated:")
+		terragruntOptions.Logger.Errorf("Not all locals could be evaluated:")
 		for _, local := range locals {
-			terragruntOptions.Logger.Debugf("\t- %s", local.Name)
+			terragruntOptions.Logger.Errorf("\t- %s", local.Name)
 		}
 		return nil, errors.WithStackTrace(CouldNotEvaluateAllLocalsError{})
 	}
@@ -135,7 +135,7 @@ func attemptEvaluateLocals(
 
 	evaluatedLocalsAsCty, err := convertValuesMapToCtyVal(evaluatedLocals)
 	if err != nil {
-		terragruntOptions.Logger.Debugf("Could not convert evaluated locals to the execution context to evaluate additional locals")
+		terragruntOptions.Logger.Errorf("Could not convert evaluated locals to the execution context to evaluate additional locals")
 		return nil, evaluatedLocals, false, err
 	}
 	evalCtx := CreateTerragruntEvalContext(

configstack/running_module.go

@@ -218,9 +218,9 @@ func (module *runningModule) waitForDependencies() error {
 
 		if doneDependency.Err != nil {
 			if module.Module.TerragruntOptions.IgnoreDependencyErrors {
-				module.Module.TerragruntOptions.Logger.Debugf("Dependency %s of module %s just finished with an error. Module %s will have to return an error too. However, because of --terragrunt-ignore-dependency-errors, module %s will run anyway.", doneDependency.Module.Path, module.Module.Path, module.Module.Path, module.Module.Path)
+				module.Module.TerragruntOptions.Logger.Errorf("Dependency %s of module %s just finished with an error. Module %s will have to return an error too. However, because of --terragrunt-ignore-dependency-errors, module %s will run anyway.", doneDependency.Module.Path, module.Module.Path, module.Module.Path, module.Module.Path)
 			} else {
-				module.Module.TerragruntOptions.Logger.Debugf("Dependency %s of module %s just finished with an error. Module %s will have to return an error too.", doneDependency.Module.Path, module.Module.Path, module.Module.Path)
+				module.Module.TerragruntOptions.Logger.Errorf("Dependency %s of module %s just finished with an error. Module %s will have to return an error too.", doneDependency.Module.Path, module.Module.Path, module.Module.Path)
 				return DependencyFinishedWithError{module.Module, doneDependency.Module, doneDependency.Err}
 			}
 		} else {

docs/_docs/02_features/debugging.md

@@ -16,11 +16,11 @@ Terragrunt and Terraform usually play well together in helping you
 write DRY, re-usable infrastructure. But how do we figure out what
 went wrong in the rare case that they _don't_ play well?
 
-Terragrunt provides a debug mode you can access through the `--terragrunt-debug`
+Terragrunt provides a way to configure logging level through the `--terragrunt-log-level`
 command flag. For example you could use it like this to debug an `apply`
 that's producing unexpected output:
 
-    $ terragrunt apply --terragrunt-debug
+    $ terragrunt apply --terragrunt-log-level debug
 
 Running this command will do two things for you:
   - Output a file named `terragrunt-debug.tfvars.json` to your terragrunt working
@@ -30,7 +30,7 @@ Running this command will do two things for you:
     `terragrunt`. This will help you to determine where the problem's root cause
     lies.
 
-The flag's goal is to help you determine which of these three major areas is the
+Using "debug" log-level is helpful when you want determine which of these three major areas is the
 root cause of your problem:
   1. Misconfiguration of your infrastructure code.
   2. An error in `terragrunt`.
@@ -93,7 +93,7 @@ You perform a `terragrunt apply`, and find that `outputs.task_ids` has 7
 elements, but you know that the cluster only has 4 VMs in it! What's happening?
 Let's figure it out. Run this:
 
-    $ terragrunt apply --terragrunt-debug
+    $ terragrunt apply --terragrunt-log-level debug
 
 After applying, you will see this output on standard error
 
@@ -126,7 +126,7 @@ Oops! It says `max` when it should be `min`. If we fix `ecs-cluster/outputs.tf`
 we should be golden! We fix the problem in time to take a nice afternoon walk in
 the sun.
 
-In this example we've seen how `terragrunt debug` can help us root cause issues
+In this example we've seen how setting `debug` log-level can help us root cause issues
 in dependency and local variable resolution.
 
 <!-- See

main.go

@@ -30,7 +30,7 @@ func checkForErrorsAndExit(err error) {
 	if err == nil {
 		os.Exit(0)
 	} else {
-		logger := util.CreateLogEntry("", true)
+		logger := util.CreateLogEntry("", "debug")
 		if os.Getenv("TERRAGRUNT_DEBUG") != "" {
 			logger.Errorln(errors.PrintErrorWithStackTrace(err))
 		} else {

options/options.go

@@ -11,7 +11,7 @@ import (
 	"github.com/gruntwork-io/terragrunt/errors"
 	"github.com/gruntwork-io/terragrunt/util"
 	"github.com/hashicorp/go-version"
-	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus"
 )
 
 var TERRAFORM_COMMANDS_WITH_SUBCOMMAND = []string{
@@ -28,6 +28,9 @@ const DEFAULT_PARALLELISM = math.MaxInt32
 // TERRAFORM_DEFAULT_PATH just takes terraform from the path
 const TERRAFORM_DEFAULT_PATH = "terraform"
 
+// DEFAULT_LOG_LEVEL defines default log level for Terragrunt
+const DEFAULT_LOG_LEVEL = "warn"
+
 const TerragruntCacheDir = ".terragrunt-cache"
 
 const DefaultTFDataDir = ".terraform"
@@ -71,7 +74,10 @@ type TerragruntOptions struct {
 	WorkingDir string
 
 	// Basic log entry
-	Logger *log.Entry
+	Logger *logrus.Entry
+
+	// Log level
+	LogLevel string
 
 	// Environment variables at runtime
 	Env map[string]string
@@ -159,7 +165,7 @@ type TerragruntOptions struct {
 
 // Create a new TerragruntOptions object with reasonable defaults for real usage
 func NewTerragruntOptions(terragruntConfigPath string) (*TerragruntOptions, error) {
-	logger := util.CreateLogEntry("", false)
+	logger := util.CreateLogEntry("", DEFAULT_LOG_LEVEL)
 
 	workingDir, downloadDir, err := DefaultWorkingAndDownloadDirs(terragruntConfigPath)
 	if err != nil {
@@ -176,6 +182,7 @@ func NewTerragruntOptions(terragruntConfigPath string) (*TerragruntOptions, erro
 		TerraformCliArgs:            []string{},
 		WorkingDir:                  workingDir,
 		Logger:                      logger,
+		LogLevel:                    DEFAULT_LOG_LEVEL,
 		Env:                         map[string]string{},
 		Source:                      "",
 		SourceUpdate:                false,
@@ -219,7 +226,7 @@ func NewTerragruntOptionsForTest(terragruntConfigPath string) (*TerragruntOption
 	opts, err := NewTerragruntOptions(terragruntConfigPath)
 
 	if err != nil {
-		logger := util.CreateLogEntry("", false)
+		logger := util.CreateLogEntry("", "warn")
 		logger.Printf("error: %v\n", errors.WithStackTrace(err))
 		return nil, err
 	}
@@ -248,7 +255,7 @@ func (terragruntOptions *TerragruntOptions) Clone(terragruntConfigPath string) *
 		NonInteractive:              terragruntOptions.NonInteractive,
 		TerraformCliArgs:            util.CloneStringList(terragruntOptions.TerraformCliArgs),
 		WorkingDir:                  workingDir,
-		Logger:                      util.CreateLogEntryWithWriter(terragruntOptions.ErrWriter, workingDir, terragruntOptions.Debug),
+		Logger:                      util.CreateLogEntryWithWriter(terragruntOptions.ErrWriter, workingDir, terragruntOptions.LogLevel),
 		Env:                         util.CloneStringMap(terragruntOptions.Env),
 		Source:                      terragruntOptions.Source,
 		SourceUpdate:                terragruntOptions.SourceUpdate,

remote/remote_state.go

@@ -112,7 +112,6 @@ func (remoteState *RemoteState) differsFrom(existingBackend *TerraformBackend, t
 	}
 
 	if !terraformStateConfigEqual(existingBackend.Config, remoteState.Config) {
-		terragruntOptions.Logger.Infof("Backend config has changed (Set environment variable TG_LOG=debug to have terragrunt log the changes)")
 		terragruntOptions.Logger.Debugf("Changed from %s to %s", existingBackend.Config, remoteState.Config)
 		return true
 	}