[Issue 18827] New: scope delegate literal allocates GC closure

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18827

          Issue ID: 18827
           Summary: scope delegate literal allocates GC closure
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: code at dawg.eu

cat > bug.d << CODE
int func(int delegate(int) dg)
{
    return dg(2);
}

int templ(alias dg)()
{
    return dg(2);
}

void bar()
{
    int a = 3;
    scope dg = (int x) => x * a;
    func(dg); // does not allocate closure, GOOD
    templ!((int x) scope => x * a)(); // does not allocate closure, GOOD
    func((int x) scope => x * a); // does allocate closure, BAD
}
CODE

Passing a delegate literal with scoped context should never allocate a closure,
but it does when the delegate is being passed by value.

With DIP1000 escaping of the context within the delegate should be statically
forbidden, right now it depends on programming correctness. Still an explicit
scope should disable allocations anyhow, though prolly mark the delegates as
unsafe.

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