fix: Fix regression in Helm post-renderer error handling

cmd/skaffold/app/cmd/filter.go

@@ -17,6 +17,7 @@ limitations under the License.
 package cmd
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -73,6 +74,8 @@ func runFilter(ctx context.Context, out io.Writer, debuggingFilters bool, postRe
 		if postRenderer != "" {
 			cmd := exec.CommandContext(ctx, postRenderer)
 			cmd.Stdin = os.Stdin
+			stderr := &bytes.Buffer{}
+			cmd.Stderr = stderr
 			stdoutPipe, err := cmd.StdoutPipe()
 			if err != nil {
 				return fmt.Errorf("running post-renderer: %w", err)
@@ -86,7 +89,10 @@ func runFilter(ctx context.Context, out io.Writer, debuggingFilters bool, postRe
 			if err != nil {
 				return fmt.Errorf("loading post-renderer result: %w", err)
 			}
-			stdoutPipe.Close()
+			err = cmd.Wait()
+			if err != nil {
+				return fmt.Errorf("error while running command %s. error output:\n%s: %v", postRenderer, stderr.String(), err)
+			}
 		} else {
 			manifestList, err = manifest.Load(os.Stdin)
 		}

cmd/skaffold/app/cmd/filter_test.go

@@ -103,3 +103,22 @@ spec:
 		})
 	}
 }
+
+func TestFilterPostRendererFailure(t *testing.T) {
+	testutil.Run(t, "user-provided post-renderer fails with non-zero exit code", func(t *testutil.T) {
+		t.Override(&opts, config.SkaffoldOptions{})
+		mockRunner := &mockDevRunner{}
+		t.Override(&createRunner, func(context.Context, io.Writer, config.SkaffoldOptions) (runner.Runner, []util.VersionedConfig, *runcontext.RunContext, error) {
+			return mockRunner, []util.VersionedConfig{&latest.SkaffoldConfig{}}, nil, nil
+		})
+		dir := t.NewTempDir().Chdir()
+		dir.Write("fail.sh", `#!/bin/sh
+echo "foo error happened" >&2
+exit 1`)
+		var b bytes.Buffer
+
+		err := runFilter(context.TODO(), &b, false, "./fail.sh", nil)
+
+		t.CheckErrorContains("error while running command ./fail.sh. error output:\nfoo error happened\n: exit status 1", err)
+	})
+}