elastic/elasticsearch · error · IllegalArgumentException

function reference [%s::%s/%d] matching [%s, %s/%d] not foun

Error message

function reference [%s::%s/%d] matching [%s, %s/%d] not found

What it means

FunctionRef.create throws this IllegalArgumentException at compile time when a method reference 'Type::methodName' cannot resolve any whitelisted Painless method (static or instance) matching the name and arity. The compiler first tries an augmented instance method lookup, then a static method lookup with adjusted arity; if both return null, no accessible method of that class with that name and parameter count exists in the Painless allowlist.

Source

Thrown at modules/lang-painless/src/main/java/org/elasticsearch/painless/FunctionRef.java:191

                boolean captured = numberOfCaptures == 1;
                PainlessMethod painlessMethod = painlessLookup.lookupPainlessMethod(
                    typeName,
                    true,
                    methodName,
                    interfaceTypeParametersSize
                );

                if (painlessMethod == null) {
                    painlessMethod = painlessLookup.lookupPainlessMethod(
                        typeName,
                        false,
                        methodName,
                        captured ? interfaceTypeParametersSize : interfaceTypeParametersSize - 1
                    );

                    if (painlessMethod == null) {
                        throw new IllegalArgumentException(
                            Strings.format(
                                "function reference [%s::%s/%d] matching [%s, %s/%d] not found",
                                typeName,
                                methodName,
                                interfaceTypeParametersSize,
                                targetClassName,
                                interfaceMethodName,
                                interfaceTypeParametersSize
                            )
                        );
                    }
                } else if (captured) {
                    throw new IllegalArgumentException(
                        Strings.format(
                            "cannot use a static method as a function reference [%s::%s/%d] with a non-static captured variable",
                            typeName,
                            methodName,
                            interfaceTypeParametersSize

View on GitHub (pinned to db6a809a66)

Solutions

1. Verify the method name is spelled correctly and exists on the referenced class.
2. Confirm the class and method are whitelisted in the Painless API (check the allowed methods list for your ES version).
3. Adjust the functional interface arity to match the method's parameter count (remember instance methods consume one parameter for the receiver).

Example fix

// before
Function<String, String> f = String::reversed;  // typo, method is 'reverse' or doesn't exist
// after
Function<StringBuilder, StringBuilder> f = StringBuilder::reverse;

// Verify the method exists and is whitelisted with matching arity:
// // Check the Painless API docs for the class's allowed methods

When it happens

Trigger: Writing 'String::fooBar' where fooBar does not exist or is not whitelisted. Writing 'List::size' when List is not allowed or size is not whitelisted. Mismatched arity: the functional interface expects N parameters but the referenced method has a different count.

Common situations: Typos in method names. Referencing methods on classes not whitelisted in Painless. Methods that exist in Java but are excluded from the Painless API surface for safety. Version differences where a method was removed or renamed.

Related errors

• cannot convert function reference [%s::%s] to a non-function
• function reference [this::%s] matching [%s, %s/%d] not found
• function reference [%s::new/%d] matching [%s, %s/%d] not fou
• cannot use a static method as a function reference [%s::%s/%
• Cannot apply operator [{}] to type [{}]

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/7498412fd9181bde. Report an issue: GitHub.