GoogleContainerTools/skaffold · error

removing unused default args

Error message

removing unused default args: %w

What it means

Wraps a failure from filterUnusedBuildArgs, which scans the Dockerfile to drop default build args that are not actually used. Failure here means the Dockerfile content could not be scanned/parsed by the filter.

Solutions

1. Read the wrapped inner error to find the parse failure point
2. Fix Dockerfile syntax around ARG declarations
3. Re-encode the Dockerfile as UTF-8 without BOM
4. Retry if the file was mid-write (I/O race)

Example fix

// before
ARG MYARG
MYARG broken line
// after
ARG MYARG
RUN echo $MYARG

// sanity-check ARG lines parse as UTF-8 text with valid syntax
b, err := os.ReadFile(absDockerfilePath)
if err != nil { return err }
if !utf8.Valid(b) { return fmt.Errorf("dockerfile is not valid UTF-8") }

args, err := evalBuildArgs(workspace, df, args, env)
if err != nil && strings.Contains(err.Error(), "removing unused default args") {
  return fmt.Errorf("Dockerfile could not be scanned; check syntax near ARG lines: %w", err)
}

When it happens

Trigger: evalBuildArgs calls filterUnusedBuildArgs(f, result) after opening the Dockerfile; the scanner errors, e.g. on a read error or Dockerfile syntax it cannot parse (malformed ARG/ONBUILD lines).

Common situations: Dockerfile with unusual constructs or encoding issues; I/O error reading a partially-written file; unexpected parser version behavior.

Related errors

• parsing dockerfile
• couldn't parse image tag
• couldn't parse image tag
• docker build failure
• normalizing dockerfile path

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/b7a5b475dc4a58de. Report an issue: GitHub.

Appendix: source

Thrown at pkg/skaffold/docker/build_args.go:79

	for k, v := range defaults {
		result[k] = &v
	}

	for k, v := range extra {
		result[k] = v
	}
	absDockerfilePath, err := NormalizeDockerfilePath(workspace, dockerfilePath)
	if err != nil {
		return nil, fmt.Errorf("normalizing dockerfile path: %w", err)
	}
	f, err := os.Open(absDockerfilePath)
	if err != nil {
		return nil, fmt.Errorf("reading dockerfile: %w", err)
	}
	defer f.Close()
	result, err = filterUnusedBuildArgs(f, result)
	if err != nil {
		return nil, fmt.Errorf("removing unused default args: %w", err)
	}
	for k, v := range args {
		result[k] = v
	}
	result, err = util.EvaluateEnvTemplateMapWithEnv(result, env)
	if err != nil {
		return nil, fmt.Errorf("unable to expand build args: %w", err)
	}
	return result, nil
}

// ArtifactResolver provides an interface to resolve built artifact tags by image name.
type ArtifactResolver interface {
	GetImageTag(imageName string) (string, bool)
}

// ResolveDependencyImages creates a map of artifact aliases to their built image from a required artifacts slice.
// If `missingIsFatal` is false then it is permissive of missing entries in the ArtifactResolver and returns nil for those entries.

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