windmill-labs/windmill · error

Problem making rule for {key}: {e}

Error message

Problem making rule for {key}: {e}

What it means

When converting each entry of `properties` into validation rules via SchemaValidationRule::from_value, any per-property failure is wrapped with this message naming the property key. The underlying cause (missing `type`, unsupported type value, bad `enum`, unsupported items, etc.) is appended after the colon, so read the chained cause to find the real problem.

Source

Thrown at backend/windmill-common/src/schema.rs:549

                v.as_str()
                    .map(|s| s.to_string())
                    .ok_or(anyhow!("required field key is not a string"))
            })
            .collect::<Result<Vec<String>, anyhow::Error>>()?;

        let properties = schema
            .get("properties")
            .ok_or(anyhow!("Missing `properties` field on schema"))?
            .as_object()
            .ok_or(anyhow!("`properties` field should be an object"))?;

        let mut rules = vec![];

        for (key, val) in properties {
            rules.push((
                key.clone(),
                SchemaValidationRule::from_value(val)
                    .map_err(|e| anyhow!("Problem making rule for {key}: {e}"))?,
            ));
        }

        Ok(Self { required, rules })
    }
}

impl JsonPrimitiveType {
    fn from_str(typ: &str) -> Result<Self, anyhow::Error> {
        match typ {
            "string" => {
                return Ok(JsonPrimitiveType::String);
            }
            "number" => {
                return Ok(JsonPrimitiveType::Number);
            }
            "integer" => {
                return Ok(JsonPrimitiveType::Integer);

View on GitHub (pinned to e474e8803c)

Solutions

1. Read the error's suffix after the colon: it names the root cause and the offending property key.
2. Fix that property's sub-schema (add/repair `type`, wrap `enum` in an array, add `items` for arrays, use `anyOf` for unions).
3. Validate the whole schema with a standard JSON Schema 2020-12 validator before deploying to catch all offending properties at once.
4. Split large schemas and test properties incrementally to isolate the failing one.

Example fix

// before
{"properties": {"count": {"typ": "integer"}}}
// after
{"properties": {"count": {"type": "integer"}}}

fn validate_all_properties(schema: &serde_json::Value) -> Result<(), String> {
    let props = schema.get("properties").and_then(|p| p.as_object())
        .ok_or("properties missing or not an object")?;
    for (key, prop) in props {
        let t = prop.get("type").ok_or_else(|| format!("{key}: missing `type`"))?;
        let ok = t.is_string()
            || t.as_array().map(|a| a.iter().all(|v| v.is_string())).unwrap_or(false);
        if !ok { return Err(format!("{key}: bad `type` value")); }
        if let Some(e) = prop.get("enum") {
            if !e.is_array() { return Err(format!("{key}: `enum` must be an array")); }
        }
        if t.as_str() == Some("array") && prop.get("items").is_none() {
            return Err(format!("{key}: array type needs `items`"));
        }
    }
    Ok(())
}

null

match Schema::from_schema(&schema_str) {
    Ok(s) => s,
    Err(e) => {
        let msg = e.to_string();
        if let Some((key, cause)) = msg.strip_prefix("Problem making rule for ")
            .and_then(|rest| rest.split_once(": ")) {
            eprintln!("invalid property `{key}`: {cause}");
        }
        return Err(e);
    }
}

When it happens

Trigger: Calling Schema::from_schema where at least one property sub-schema is invalid — e.g. {"properties": {"bad": {"enum": "x"}}} yields "Problem making rule for bad: enum variants are not in an array". Reached during app reduction (reduce_app) when an inline script schema is deployed.

Common situations: One malformed property among many valid ones — typos in `type`, unsupported keywords per property (e.g. patternProperties, oneOf instead of anyOf), items missing on array types — often inside app/schemas generated by AI or templates.

Related errors

• Unsupported value for type field, expected string or string
• enum variants are not in an array
• Supplied schema draft version is unsuported
• No draft version supplied
• Missing `required` field on schema

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/db3f4caf950939ca. Report an issue: GitHub.