ADDITIONAL SYSTEM INFORMATION :
Any OpenJDK version 1.8 onward, any platform. Tested and verified on 1.8.0_60-b27 and 18.9 (build 11+28) on Windows 7.

A DESCRIPTION OF THE PROBLEM :
If an anonymous or local inner class is declared inside of a lambda, the `EnclosingMethod` attribute on that class refers to the compiler-generated "lambda$" method rather than the method that enclosed the original declaration.

This is a violation of JVMS §4.7.7 ("The EnclosingMethod Attribute"):

> It is the responsibility of a Java compiler to ensure that the method identified via the `method_index` is indeed the closest **lexically enclosing** method of the class that contains this `EnclosingMethod` attribute.

Emphasis mine. Currently, if the class containing an `EnclosingMethod` attribute was declared within a lambda expression, the attribute refers to a method that never existed in the lexical scope.

A particularly vexing side effect of this occurs when the generic signature of a lambda-embedded inner type contains type variables declared by the lexically enclosing method. Those type variables will be out of scope from the perspective of the method identified by the `EnclosingMethod` attribute. Consequently, the `java.lang.reflect` APIs cannot resolve them.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run attached "source code for an executable test case". Note the output.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Output should be:

[class LambdaBug$1] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.immediateScope()
[class LambdaBug$1ExplicitToken] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.immediateScope()
[class LambdaBug$2] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.lambdaScope()
[class LambdaBug$2ExplicitToken] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.lambdaScope()

ACTUAL -
Output is actually:

[class LambdaBug$1] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.immediateScope()
[class LambdaBug$1ExplicitToken] EnclosingClass=class LambdaBug; EnclosingMethod=static void LambdaBug.immediateScope()
[class LambdaBug$2] EnclosingClass=class LambdaBug; EnclosingMethod=private static void LambdaBug.lambda$lambdaScope$0()
[class LambdaBug$2ExplicitToken] EnclosingClass=class LambdaBug; EnclosingMethod=private static void LambdaBug.lambda$lambdaScope$0()


---------- BEGIN SOURCE ----------
class LambdaBug<T> {
    protected LambdaBug() {
        System.out.printf("[%s] EnclosingClass=%s; EnclosingMethod=%s%n",
                         getClass(),
                         getClass().getEnclosingClass(),
                         getClass().getEnclosingMethod());
    }

    static <X> void immediateScope() {
        class ExplicitToken extends LambdaBug<X> {}
        new LambdaBug<X>() {};
        new ExplicitToken();
    }

    static <X> void lambdaScope() {
        Runnable r = () -> {
            class ExplicitToken extends LambdaBug<X> {}
            new LambdaBug<X>() {};
            new ExplicitToken();
        };
        r.run();
    }

    public static void main(final String[] args) {
        immediateScope();
        lambdaScope();
    }
}
---------- END SOURCE ----------

FREQUENCY : always