apache/skywalking · error · IllegalArgumentException

castType:{castType} is legal, context expression:{originalEx

Error message

castType:{castType} is legal, context expression:{originalExpression}

What it means

TypeCastUtil.withCast wraps an OAL attribute expression with a Java cast call during code generation. Only '(str->long)', '(long)', '(str->int)' and '(int)' are recognized; anything else hits default and throws. (Note the message text says 'is legal' but it means 'is illegal' — a long-standing wording quirk.)

Source

Thrown at oap-server/oal-rt/src/main/java/org/apache/skywalking/oal/v2/util/TypeCastUtil.java:39

public class TypeCastUtil {
    /**
     * @param castType           to change the value of given original expression.
     * @param originalExpression to read the value
     * @return cast expression if cast type exists and is legal.
     */
    public static String withCast(String castType, String originalExpression) {
        if (castType == null) {
            return originalExpression;
        }
        switch (castType) {
            case "(str->long)":
            case "(long)":
                return "Long.parseLong(" + originalExpression + ")";
            case "(str->int)":
            case "(int)":
                return "Integer.parseInt(" + originalExpression + ")";
            default:
                throw new IllegalArgumentException(
                    "castType:" + castType + " is legal, context expression:" + originalExpression);
        }
    }
}

View on GitHub (pinned to 102af09b4a)

Solutions

1. Use only the supported casts: (str->long) / (long) and (str->int) / (int)
2. If a double/boolean conversion is needed, preprocess the value upstream (e.g. in MAL/LAL or the agent) so the OAL source attribute is already numeric
3. Remove the cast entirely if the attribute is already the right type

Example fix

// before (OAL)
latency = from Span.tag('lat')(str->double).avg() --> latencyAvg
// after
latency = from Span.tag('lat')(str->long).avg() --> latencyAvg

// Lint OAL casts before deploy:
Set<String> ok = Set.of("(str->long)", "(long)", "(str->int)", "(int)");
for (String cast : castsUsed(script)) {
    if (!ok.contains(cast)) throw new ConfigException("Unsupported OAL cast: " + cast);
}

In OAL validation tooling, catch IllegalArgumentException from the enricher and surface it with the rule's file:line; do not catch in OAP startup.

When it happens

Trigger: An OAL expression uses an unsupported cast such as (str->double), (str->boolean), or a typo like (string->long). The grammar may accept the cast token but the code generator has no lowering for it.

Common situations: Trying to cast a string metric attribute to a type other than long/int (e.g. building a double metric from a tag); typo in the cast syntax; assuming SQL-style CAST semantics in OAL.

Related errors

• filter expression [{}] not found
• Can't find metrics, {}
• Unknown filter value type: {}
• Unsupported number operator: {}
• Unsupported string operator: {}

AI-assisted analysis of apache/skywalking@102af09b4a (2026-08-14). Data as JSON: /api/errors/70da16a71855c109. Report an issue: GitHub.