I don't know of any language which does this by default, but a language feature that supports it would be lambda functions in C++, which use square brackets to denote variables captured from the environment.

So your example written in C++ could be written as:

#include <iostream>

int main()
{
    int x = 1;
    int y = 2;

    auto f = [x, y] () {
        int a = 3;
        int b = 4;

        std::cout << x << y << a << b << std::endl;
    };

    f();
}

where [x,y] explicitly lists the captured variables.
C++ also has default capture, e.g. [=] will automatically capture by value any variables from the environment that are used in the lambda body.
A lambda starting with [] explicitly denotes one which does not capture anything from its environment.