argoproj/argo-workflows · error

failed to evaluate workflow %s expression: %w

Error message

failed to evaluate workflow %s expression: %w

What it means

Raised by Operation.evaluateStringExpression when the workflowMetadata name/generateName/label/annotation expression from the EventBinding's submit.ObjectMeta either fails expr.Compile (syntax/type error) or expr.Run (runtime evaluation error). Compile and run failures are wrapped with the same message, distinguished only by the inner %w error text. It aborts dispatch because the workflow metadata cannot be populated.

Source

Thrown at server/event/dispatch/operation.go:218

	for annotationKey, annotationValue := range metadata.Annotations {
		evalAnnotation, err := o.evaluateStringExpression(annotationValue, fmt.Sprintf("annotation \"%s\"", annotationKey))
		if err != nil {
			return err
		}
		// See labels comment above.
		if wf.Annotations == nil {
			wf.Annotations = map[string]string{}
		}
		wf.Annotations[annotationKey] = evalAnnotation
	}
	return nil
}

func (o *Operation) evaluateStringExpression(statement string, errorInfo string) (string, error) {
	env := exprenv.GetFuncMap(o.env)
	program, err := expr.Compile(statement, expr.Env(env))
	if err != nil {
		return "", fmt.Errorf("failed to evaluate workflow %s expression: %w", errorInfo, err)
	}
	result, err := expr.Run(program, env)
	if err != nil {
		return "", fmt.Errorf("failed to evaluate workflow %s expression: %w", errorInfo, err)
	}

	v, ok := result.(string)
	if !ok {
		return "", fmt.Errorf("workflow %s expression must evaluate to a string, not a %T", errorInfo, result)
	}
	return v, nil
}

func expressionEnvironment(ctx context.Context, namespace, discriminator string, payload *wfv1.Item) (map[string]any, error) {
	src := map[string]any{
		"namespace":     namespace,
		"discriminator": discriminator,
		"metadata":      metaData(ctx),

View on GitHub (pinned to 35bff19146)

Solutions

1. Read the wrapped %w error: compile errors point to syntax (fix quoting/parens in the YAML value), runtime errors point to unknown names or nil field access
2. Verify the expression only uses the dispatch environment: namespace, discriminator, metadata, payload (plus the expr/sprig func map), and that the payload path exists — e.g. `payload.body.id` not `payload.data.id`
3. Guard against missing payload fields with defaults: `default("unknown", payload.body.id)` or existence checks
4. Test the expression locally with a sample payload using the same env before updating the EventBinding

Example fix

// before (typo + missing field)
workflowMetadata:
  labels:
    branch: paylod.body.repo.branch
// after
workflowMetadata:
  labels:
    branch: default("unknown", payload.body.repo.branch)

// Compile-check metadata expressions with the dispatch env before submitting
env := exprenv.GetFuncMap(dispatchEnv)
if _, err := expr.Compile(statement, expr.Env(env)); err != nil {
    return fmt.Errorf("invalid workflowMetadata expression %q: %w", statement, err)
}

When it happens

Trigger: EventBinding submit.workflowMetadata contains name, generateName, labels, or annotations values that are invalid expr syntax (e.g. unbalanced quotes/parens) or reference unknown identifiers/functions at runtime (e.g. typo like `paylod.body.id`, calling a function not in exprenv.GetFuncMap, indexing a nil/absent payload field).

Common situations: Typo in the expression (`payload` misspelled, wrong body key); expression uses a field the sensor payload lacks (nil map access at runtime); using a sprig/expr function not available in the dispatch env; copy-pasting an expression from a CronWorkflow where the environment differs; quoting mistakes in YAML that mangle the expression.

Related errors

• failed to compile workflow template parameter %s expression:
• failed to convert result to JSON "%s" expression: %w
• workflow %s expression must evaluate to a string, not a %T
• failed to evaluate workflow template parameter "%s" expressi
• single branch mode without a branch specified

AI-assisted analysis of argoproj/argo-workflows@35bff19146 (2026-09-03). Data as JSON: /api/errors/eec33eb5211638ed. Report an issue: GitHub.