add checksum_cmd directive to command

.gitignore

@@ -26,3 +26,4 @@ _lets
 coverage.out
 node_modules
 TODO
+.DS_Store

checksum/checksum.go

@@ -5,8 +5,10 @@ import (
 	"crypto/sha1"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sort"
+	"strings"
 
 	"github.com/lets-cli/lets/set"
 	"github.com/lets-cli/lets/util"
@@ -99,6 +101,18 @@ func getChecksumsKeys(mapping map[string][]string) []string {
 	return keys
 }
 
+func CalculateChecksumFromCmd(shell string, workDir string, script string) (string, error) {
+	cmd := exec.Command(shell, "-c", script)
+
+	out, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("can not calculate checksum from cmd: %s: %w", script, err)
+	}
+
+	res := string(out)
+	return strings.TrimSpace(res), nil
+}
+
 // CalculateChecksumFromSources calculates checksum from checksumSources.
 func CalculateChecksumFromSources(workDir string, checksumSources map[string][]string) (map[string]string, error) {
 	checksumMap := make(map[string]string)

config/config/command.go

@@ -33,6 +33,7 @@ type Command struct {
 	Depends         *Deps
 	ChecksumMap     map[string]string
 	PersistChecksum bool
+	ChecksumCmd     string
 	// args from 'lets run --debug' will become [--debug]
 	Args []string
 
@@ -68,6 +69,7 @@ func (c *Command) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		After           string
 		Ref             string
 		Checksum        *Checksum
+		ChecksumCmd     string `yaml:"checksum_cmd"`
 		PersistChecksum bool `yaml:"persist_checksum"`
 	}
 
@@ -109,6 +111,10 @@ func (c *Command) UnmarshalYAML(unmarshal func(interface{}) error) error {
 		c.ChecksumSources = *cmd.Checksum
 	}
 
+	if cmd.ChecksumCmd != "" {
+		c.ChecksumCmd = cmd.ChecksumCmd
+	}
+
 	c.PersistChecksum = cmd.PersistChecksum
 	if len(c.ChecksumSources) == 0 && c.PersistChecksum {
 		return errors.New("'persist_checksum' must be used with 'checksum'")
@@ -154,6 +160,7 @@ func (c *Command) Clone() *Command {
 		Depends:            c.Depends.Clone(),
 		ChecksumMap:        cloneMap(c.ChecksumMap),
 		PersistChecksum:    c.PersistChecksum,
+		ChecksumCmd:        c.ChecksumCmd,
 		ChecksumSources:    cloneMapSlice(c.ChecksumSources),
 		persistedChecksums: cloneMap(c.persistedChecksums),
 		Args:               cloneSlice(c.Args),
@@ -190,7 +197,17 @@ func (c *Command) Help() string {
 	return strings.TrimSuffix(buf.String(), "\n")
 }
 
-func (c *Command) ChecksumCalculator(workDir string) error {
+func (c *Command) ChecksumCalculator(shell, workDir string) error {
+	if c.ChecksumCmd != "" {
+		checksumResult, err := checksum.CalculateChecksumFromCmd(shell, workDir, c.ChecksumCmd)
+		if err != nil {
+			return err
+		}
+		c.ChecksumMap = make(map[string]string, 1)
+		c.ChecksumMap[checksum.DefaultChecksumKey] = checksumResult
+		return nil
+	}
+
 	if len(c.ChecksumSources) == 0 {
 		return nil
 	}

executor/executor.go

@@ -173,7 +173,7 @@ func (e *Executor) initCmd(ctx *Context) error {
 	}
 
 	// calculate checksum if needed
-	if err := cmd.ChecksumCalculator(e.cfg.WorkDir); err != nil {
+	if err := cmd.ChecksumCalculator(e.cfg.Shell, e.cfg.WorkDir); err != nil {
 		return fmt.Errorf("failed to calculate checksum for command '%s': %w", cmd.Name, err)
 	}
 

lets.yaml

@@ -115,3 +115,7 @@ commands:
   run-docs:
     work_dir: docs
     cmd: npm start
+
+  x:
+    checksum_cmd: echo xxx_checksum
+    cmd: echo checksum for x is ${LETS_CHECKSUM}