Only allow arg substitution in Labels field

Earlier commits allowed substitution in various places in the Image
Config. This commit reverts most of those changes and allows arg
substitution only in the `Labels` field of the image config.

Signed-off-by: Peter Engelbert <[email protected]>

Author: pmengelbert

load.go

@@ -199,10 +199,8 @@ func (s *Spec) SubstituteArgs(env map[string]string, opts ...SubstituteOpt) erro
 		}
 	}
 
-	if s.Image != nil {
-		if err := s.Image.processBuildArgs(lex, args, cfg.AllowArg); err != nil {
-			appendErr(errors.Wrap(err, "package config"))
-		}
+	if err := s.Image.processBuildArgs(lex, args, cfg.AllowArg); err != nil {
+		appendErr(errors.Wrap(err, "package config"))
 	}
 
 	if err := s.Dependencies.processBuildArgs(args, cfg.AllowArg); err != nil {
@@ -460,23 +458,11 @@ func (b *ArtifactBuild) processBuildArgs(lex *shell.Lex, args map[string]string,
 }
 
 func (img *ImageConfig) processBuildArgs(lex *shell.Lex, args map[string]string, allowArg func(string) bool) error {
-	var errs error
-	for _, p := range []*string{&img.Base, &img.Cmd, &img.User, &img.Entrypoint, &img.StopSignal, &img.WorkingDir} {
-		updated, err := expandArgs(lex, *p, args, allowArg)
-		if err != nil {
-			errs = goerrors.Join(errs, errors.Wrap(err, "imgconfig"))
-		}
-		*p = updated
+	if img == nil {
+		return nil
 	}
 
-	for i, s := range img.Env {
-		updated, err := expandArgs(lex, s, args, allowArg)
-		if err != nil {
-			errs = goerrors.Join(errs, errors.Wrapf(err, "env %s", s))
-			continue
-		}
-		img.Env[i] = updated
-	}
+	var errs error
 
 	for k, v := range img.Labels {
 		updated, err := expandArgs(lex, v, args, allowArg)
@@ -487,28 +473,5 @@ func (img *ImageConfig) processBuildArgs(lex *shell.Lex, args map[string]string,
 		img.Labels[k] = updated
 	}
 
-	if img.Post != nil {
-		for k, sl := range img.Post.Symlinks {
-			updatedK, err := expandArgs(lex, k, args, allowArg)
-			if err != nil {
-				errs = goerrors.Join(errs, errors.Wrapf(err, "symlink oldpath"))
-				continue
-			}
-
-			updatedV, err := expandArgs(lex, sl.Path, args, allowArg)
-			if err != nil {
-				errs = goerrors.Join(errs, errors.Wrapf(err, "symlink newpath"))
-				continue
-			}
-
-			sl.Path = updatedV
-			img.Post.Symlinks[updatedK] = sl
-			// remove the old key if a substitution happened
-			if updatedK != k {
-				delete(img.Post.Symlinks, k)
-			}
-		}
-	}
-
 	return errs
 }

target.go

@@ -63,10 +63,8 @@ func (t *Target) processBuildArgs(lex *shell.Lex, args map[string]string, allowA
 		}
 	}
 
-	if t.Image != nil {
-		if err := t.Image.processBuildArgs(lex, args, allowArg); err != nil {
-			errs = append(errs, errors.Wrap(err, "package config"))
-		}
+	if err := t.Image.processBuildArgs(lex, args, allowArg); err != nil {
+		errs = append(errs, errors.Wrap(err, "package config"))
 	}
 
 	if err := t.Dependencies.processBuildArgs(args, allowArg); err != nil {