Improve error handling and parameter validation

Signed-off-by: Ricardo Matsui <ricmatsui@gmail.com>

Author: ricmatsui

cmd/sops/main.go

@@ -198,6 +198,10 @@ func main() {
 
 				if c.Bool("background") {
 					log.Warn("exec-env's --background option is deprecated and will be removed in a future version of sops")
+
+					if c.Bool("same-process") {
+						return common.NewExitError("Error: The --same-process flag cannot be used with --background", codes.ErrorConflictingParameters)
+					}
 				}
 
 				tree, err := decryptTree(opts)

cmd/sops/subcommand/exec/exec.go

@@ -2,6 +2,7 @@ package exec
 
 import (
 	"bytes"
+	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -116,6 +117,10 @@ func ExecWithEnv(opts ExecOpts) error {
 		SwitchUser(opts.User)
 	}
 
+	if runtime.GOOS == "windows" && opts.SameProcess {
+		return fmt.Errorf("The --same-process flag is not supported on Windows")
+	}
+
 	var env []string
 
 	if !opts.Pristine {