overlays/morph/dry-run.patch

   1 diff --git a/morph.go b/morph.go
   2 index a88414b..e5894df 100644
   3 --- a/morph.go
   4 +++ b/morph.go
   5 @@ -542,6 +542,7 @@ func getNixContext() *nix.NixContext {
   6         return &nix.NixContext{
   7                 EvalMachines:    filepath.Join(assetRoot, assets.Friendly, "eval-machines.nix"),
   8                 ShowTrace:       showTrace,
   9 +               DryRun:          *dryRun,
  10                 KeepGCRoot:      *keepGCRoot,
  11                 AllowBuildShell: *allowBuildShell,
  12         }
  13 @@ -574,8 +575,10 @@ func buildHosts(hosts []nix.Host) (resultPath string, err error) {
  14                 return
  15         }
  16
  17 -       fmt.Fprintln(os.Stderr, "nix result path: ")
  18 -       fmt.Println(resultPath)
  19 +       if resultPath != "" {
  20 +               fmt.Fprintln(os.Stderr, "nix result path: ")
  21 +               fmt.Println(resultPath)
  22 +       }
  23         return
  24  }
  25
  26 diff --git a/nix/nix.go b/nix/nix.go
  27 index 6a9cfd5..0f7884b 100644
  28 --- a/nix/nix.go
  29 +++ b/nix/nix.go
  30 @@ -49,6 +49,7 @@ type Deployment struct {
  31  type NixContext struct {
  32         EvalMachines    string
  33         ShowTrace       bool
  34 +       DryRun          bool
  35         KeepGCRoot      bool
  36         AllowBuildShell bool
  37  }
  38 @@ -269,6 +270,10 @@ func (ctx *NixContext) BuildMachines(deploymentPath string, hosts []Host, nixArg
  39                 args = append(args, "--show-trace")
  40         }
  41
  42 +       if ctx.DryRun {
  43 +               args = append(args, "--dry-run")
  44 +       }
  45 +
  46         if nixBuildTargets != "" {
  47                 args = append(args,
  48                         "--arg", "buildTargets", nixBuildTargets)
  49 @@ -308,6 +313,10 @@ func (ctx *NixContext) BuildMachines(deploymentPath string, hosts []Host, nixArg
  50                 return resultPath, errors.New(errorMessage)
  51         }
  52
  53 +       if ctx.DryRun {
  54 +               return "", err
  55 +       }
  56 +
  57         resultPath, err = os.Readlink(resultLinkPath)
  58         if err != nil {
  59                 return "", err