Comprehensions & capture

[jvasileff]

Similar to https://github.com/ceylon/ceylon-compiler/issues/2304, this:

shared
void comprehensionCaptureTest() {
    print("* comprehensionCaptureTest begin");

    value values = [ 100, 110, 120 ];
    value valuesNull = [ 100, 110, 120, null ];

    // capture test 0
    value funcs0 = {
        for (v in values)
        ()=>v
    };
    printAll({ for (f in funcs0.sequence()) f() });
    //assert({ for (f in funcs0.sequence()) f() }.sequence().equals(values));

    // capture test 1
    value funcs1 = {
        for (v in valuesNull)
        if (exists w=v)
        ()=>w
    };
    printAll({ for (f in funcs1.sequence()) f() });
    //assert({ for (f in funcs1.sequence()) f() }.sequence().equals(values));

    // capture test 2
    value funcs2 = {
        for (v in values)
        if (exists w = true then (()=>v))
        w
    };
    printAll({ for (f in funcs2.sequence()) f() });
    //assert({ for (f in funcs2.sequence()) f() }.sequence().equals(values));

    // capture test 3
    value funcs3 = {
        for (v in values)
        for (w in { ()=>v })
        w
    };
    printAll({ for (f in funcs3.sequence()) f() });
    //assert({ for (f in funcs3.sequence()) f() }.sequence().equals(values));

    print("* comprehensionCaptureTest end");
}

produces

* comprehensionCaptureTest begin
100, 110, 120
<null>, <null>, <null>

* comprehensionCaptureTest end

rather than the expected

* comprehensionCaptureTest begin
100, 110, 120
100, 110, 120
100, 110, 120
100, 110, 120
* comprehensionCaptureTest end