apache/skywalking · error · IllegalArgumentException

Cannot parse interpolation expression: {expr}

Error message

Cannot parse interpolation expression: {expr}

What it means

The internal counterpart of the previous two: MeterSystem.createInternal cannot find functionName in the function register. All public create overloads delegate here after resolving the data type, so the same root cause (unknown @MeterFunction name) surfaces at this line depending on which overload was entered.

Source

Thrown at oap-server/analyzer/log-analyzer/src/main/java/org/apache/skywalking/oap/log/analyzer/v2/compiler/LALScriptParser.java:1062

    /**
     * Parses a standalone valueAccess expression string by wrapping it in
     * a minimal LAL script and extracting the parsed ValueAccess.
     */
    private static ValueAccess parseValueAccessExpr(final String expr) {
        // Wrap in: filter { if (EXPR) { sink {} } }
        // The expression becomes a condition, parsed as ExprCondition
        // whose ValueAccess is what we want.
        final String wrapper = "filter { if (" + expr + ") { sink {} } }";
        final LALScriptModel model = parse(wrapper);
        final IfBlock ifBlock = (IfBlock) model.getStatements().get(0);
        final LALScriptModel.Condition cond = ifBlock.getCondition();
        if (cond instanceof ExprCondition) {
            return ((ExprCondition) cond).getExpr();
        }
        if (cond instanceof ComparisonCondition) {
            return ((ComparisonCondition) cond).getLeft();
        }
        throw new IllegalArgumentException(
            "Cannot parse interpolation expression: " + expr);
    }
}

View on GitHub (pinned to 102af09b4a)

Solutions

1. Log/verify the exact functionName string against the registered names (inspect the @MeterFunction(functionName=...) values on the classpath)
2. Fix the rule or caller to use a registered name
3. Redeploy the custom function jar intact and confirm OAP boots without classload errors

Example fix

// before
meterSystem.create("my_metric", "avgerage", ScopeType.SERVICE, pool, cl, opt);
// after
meterSystem.create("my_metric", "avg", ScopeType.SERVICE, pool, cl, opt);

catch (IllegalArgumentException e) { log.error("meter creation failed: {}", e.getMessage()); /* reject the single rule, don't crash the receiver */ }

When it happens

Trigger: Any meter creation path whose functionName lookup misses — MAL rule compilation, custom code calling MeterSystem.create directly with a wrong name, or a custom function class that failed to load during the boot scan (broken jar suppressed the registration).

Common situations: Direct MeterSystem API use in custom receivers; a partially deployed custom-plugin jar where some classes failed to load; renaming a function without updating all rule files.

Related errors

• Unsupported extractor statement in LAL rule at line {sourceL
• {slot} value '{numText}' exceeds the supported range (must f
• {slot} value '{numText}' exceeds the supported range (must f
• Unclosed interpolation in: {s}
• tag() requires exactly one string literal argument, e.g. tag

AI-assisted analysis of apache/skywalking@102af09b4a (2026-08-14). Data as JSON: /api/errors/666888c6ae9cf3a4. Report an issue: GitHub.