Copy lock file only when needed

util/file.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"bytes"
 	"encoding/gob"
 	"io"
 	"os"
@@ -584,15 +585,47 @@ func (err PathIsNotFile) Error() string {
 // 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 *logrus.Entry) error {
-	sourceLockFilePath := JoinPath(sourceFolder, TerraformLockFile)
-	destinationLockFilePath := JoinPath(destinationFolder, TerraformLockFile)
+	sourceLockFilePath, sourceErr := filepath.Abs(JoinPath(sourceFolder, TerraformLockFile))
+	if sourceErr != nil {
+		return errors.WithStackTrace(sourceErr)
+	}
+	destinationLockFilePath, destErr := filepath.Abs(JoinPath(destinationFolder, TerraformLockFile))
+	if destErr != nil {
+		return errors.WithStackTrace(destErr)
+	}
 
-	if FileExists(sourceLockFilePath) {
-		logger.Debugf("Copying lock file from %s to %s", sourceLockFilePath, destinationFolder)
-		return CopyFile(sourceLockFilePath, destinationLockFilePath)
+	if sourceLockFilePath == destinationLockFilePath {
+		logger.Debugf("Source and destination lock file paths are the same: %s. Not copying.", sourceLockFilePath)
+		return nil
 	}
 
-	return nil
+	if !FileExists(sourceLockFilePath) {
+		logger.Debugf("Source lock file does not exist: %s. Not copying.", sourceLockFilePath)
+		return nil
+	}
+
+	sourceContents, sourceReadErr := os.ReadFile(sourceLockFilePath)
+	if sourceReadErr != nil {
+		return errors.WithStackTrace(sourceReadErr)
+	}
+
+	if !FileExists(destinationLockFilePath) {
+		logger.Debugf("Destination lock file does not exist: %s. Copying.", destinationLockFilePath)
+		return WriteFileWithSamePermissions(sourceLockFilePath, destinationLockFilePath, sourceContents)
+	}
+
+	destinationContents, destReadErr := os.ReadFile(destinationLockFilePath)
+	if destReadErr != nil {
+		return errors.WithStackTrace(destReadErr)
+	}
+
+	if bytes.Equal(sourceContents, destinationContents) {
+		logger.Debugf("Source and destination lock file contents are the same. Not copying.")
+		return nil
+	}
+
+	logger.Debugf("Copying lock file from %s to %s", sourceLockFilePath, destinationFolder)
+	return WriteFileWithSamePermissions(sourceLockFilePath, destinationLockFilePath, sourceContents)
 }
 
 // ListTfFiles returns a list of all TF files in the specified directory.

util/file_test.go

@@ -2,6 +2,8 @@ package util
 
 import (
 	"errors"
+	"io"
+	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
@@ -11,6 +13,7 @@ import (
 	"fmt"
 
 	"github.com/gruntwork-io/terragrunt/test/helpers"
+	"github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -336,5 +339,116 @@ func TestEmptyDir(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, testCase.expectEmpty, emptyValue, "For path %s", testCase.path)
 	}
+}
+
+func TestCopyLockFile(t *testing.T) {
+	logger := logrus.New()
+	logger.Out = io.Discard
+	loggerEntry := logger.WithFields(logrus.Fields{})
+
+	t.Run("SameSourceAndDestination", func(t *testing.T) {
+		sourceFolder := "/path/to/folder"
+		destinationFolder := "/path/to/folder"
+
+		err := CopyLockFile(sourceFolder, destinationFolder, loggerEntry)
+		assert.NoError(t, err)
+	})
+
+	t.Run("SourceLockFileDoesNotExist", func(t *testing.T) {
+		sourceFolder := "/path/to/folder"
+		destinationFolder := "/path/to/destination"
+
+		err := CopyLockFile(sourceFolder, destinationFolder, loggerEntry)
+		assert.NoError(t, err)
+	})
+
+	t.Run("DestinationLockFileDoesNotExist", func(t *testing.T) {
+		sourceFolder := t.TempDir()
+		destinationFolder := t.TempDir()
+
+		sourceLockFilePath := filepath.Join(sourceFolder, TerraformLockFile)
+		destinationLockFilePath := filepath.Join(destinationFolder, TerraformLockFile)
+
+		// Create source lock file
+		err := ioutil.WriteFile(sourceLockFilePath, []byte("lock file contents"), 0644)
+		require.NoError(t, err)
+
+		err = CopyLockFile(sourceFolder, destinationFolder, loggerEntry)
+		assert.NoError(t, err)
+
+		// Verify destination lock file exists
+		_, err = os.Stat(destinationLockFilePath)
+		assert.NoError(t, err)
+
+		// Verify destination lock file contents
+		destinationContents, err := ioutil.ReadFile(destinationLockFilePath)
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("lock file contents"), destinationContents)
+
+		// Clean up
+		err = os.Remove(sourceLockFilePath)
+		assert.NoError(t, err)
+		err = os.Remove(destinationLockFilePath)
+		assert.NoError(t, err)
+	})
+
+	t.Run("SameContents", func(t *testing.T) {
+		sourceFolder := t.TempDir()
+		destinationFolder := t.TempDir()
 
+		sourceLockFilePath := filepath.Join(sourceFolder, TerraformLockFile)
+		destinationLockFilePath := filepath.Join(destinationFolder, TerraformLockFile)
+
+		// Create source lock file
+		err := ioutil.WriteFile(sourceLockFilePath, []byte("lock file contents"), 0644)
+		require.NoError(t, err)
+
+		// Create destination lock file with same contents
+		err = ioutil.WriteFile(destinationLockFilePath, []byte("lock file contents"), 0644)
+		require.NoError(t, err)
+
+		err = CopyLockFile(sourceFolder, destinationFolder, loggerEntry)
+		assert.NoError(t, err)
+
+		// Verify destination lock file contents remain the same
+		destinationContents, err := ioutil.ReadFile(destinationLockFilePath)
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("lock file contents"), destinationContents)
+
+		// Clean up
+		err = os.Remove(sourceLockFilePath)
+		assert.NoError(t, err)
+		err = os.Remove(destinationLockFilePath)
+		assert.NoError(t, err)
+	})
+
+	t.Run("DifferentContents", func(t *testing.T) {
+		sourceFolder := t.TempDir()
+		destinationFolder := t.TempDir()
+
+		sourceLockFilePath := filepath.Join(sourceFolder, TerraformLockFile)
+		destinationLockFilePath := filepath.Join(destinationFolder, TerraformLockFile)
+
+		// Create source lock file
+		err := ioutil.WriteFile(sourceLockFilePath, []byte("lock file contents"), 0644)
+		require.NoError(t, err)
+
+		// Create destination lock file with different contents
+		err = ioutil.WriteFile(destinationLockFilePath, []byte("different contents"), 0644)
+		require.NoError(t, err)
+
+		err = CopyLockFile(sourceFolder, destinationFolder, loggerEntry)
+		assert.NoError(t, err)
+
+		// Verify destination lock file contents are updated
+		destinationContents, err := ioutil.ReadFile(destinationLockFilePath)
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("lock file contents"), destinationContents)
+
+		// Clean up
+		err = os.Remove(sourceLockFilePath)
+		assert.NoError(t, err)
+		err = os.Remove(destinationLockFilePath)
+		assert.NoError(t, err)
+	})
 }