dagger/dagger · error

failed to convert anyOf variant %d: %w

Error message

failed to convert anyOf variant %d: %w

What it means

While expanding an anyOf field, each variant is recursively converted with bbiSchemaToGenaiSchema. This error wraps the failure of the variant at index i, so a nested schema inside anyOf is malformed (bad description type, bad items, non-map properties, etc.).

Source

Thrown at core/llm_google.go:554

		DisplaySpans:     displaySpans,
		ToolCallDisplays: toolCallDisplays,
	}, nil
}

// TODO: this definitely needs a unit test
func bbiSchemaToGenaiSchema(bbi map[string]any) (*genai.Schema, error) {
	schema := &genai.Schema{}
	for key, param := range bbi {
		switch key {
		case "anyOf":
			variants, err := toSchemaMaps(param)
			if err != nil {
				return nil, fmt.Errorf("failed to convert anyOf field: %w", err)
			}
			for i, variant := range variants {
				variantSchema, err := bbiSchemaToGenaiSchema(variant)
				if err != nil {
					return nil, fmt.Errorf("failed to convert anyOf variant %d: %w", i, err)
				}
				schema.AnyOf = append(schema.AnyOf, variantSchema)
			}
		case "description":
			if schema.Description != "" {
				schema.Description += " "
			}
			desc, ok := param.(string)
			if !ok {
				return nil, fmt.Errorf("description must be a string, got %T", param)
			}
			schema.Description += desc
		case "properties":
			props, err := bbiPropertiesToGenaiSchemas(param)
			if err != nil {
				return nil, err
			}
			schema.Properties = props

View on GitHub (pinned to 82ba2681db)

Solutions

1. Check the variant index %d in the message and validate that variant object
2. Ensure every anyOf variant is a valid map[string]any schema with string-typed description/format
3. Recursively validate nested schemas before registering the tool
4. Simplify the anyOf into separate flat schemas if the variant is complex

Example fix

// before
"anyOf": [{"type": "string"}, {"description": 42}]
// after
"anyOf": [{"type": "string"}, {"type": "string", "description": "a string"}]

func validateVariants(s map[string]any) error {
    variants, _ := s["anyOf"].([]any)
    for i, v := range variants {
        m, ok := v.(map[string]any)
        if !ok { return fmt.Errorf("variant %d not a map", i) }
        if d, present := m["description"]; present {
            if _, ok := d.(string); !ok { return fmt.Errorf("variant %d description not a string", i) }
        }
    }
    return nil
}

func isSchemaVariant(v any) (*map[string]any, bool) {
    m, ok := v.(map[string]any)
    return &m, ok
}

schema, err := bbiSchemaToGenaiSchema(bbi)
if err != nil {
    var idx int
    if _, scan := fmt.Sscanf(err.Error(), "failed to convert anyOf variant %d", &idx); scan == nil {
        return fmt.Errorf("invalid anyOf variant at index %d: %w", idx, err)
    }
    return err
}

When it happens

Trigger: A tool schema with anyOf where one of the variant objects is itself invalid, e.g. anyOf:[{"type":"string"},{"description":123}] or a variant with items as a non-map; reached through convertToolsToGenai or nested anyOf.

Common situations: Deeply nested schemas composed programmatically where a generator emitted an invalid variant; copy-pasted JSON Schema fragments that Google's GenAI schema subset does not accept.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• failed to convert anyOf field: %w
• items must be a map, got %T
• description must be a string, got %T
• format must be a string, got %T
• failed to convert items schema: %w

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/d803f1c814de199a. Report an issue: GitHub.