[Issue 18694] New: pure functions using static/global structs with no fields should pass compilation

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18694

          Issue ID: 18694
           Summary: pure functions using static/global structs with no
                    fields should pass compilation
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: andrei at erdani.com

Consider:

struct S { enum int x = 42; }
static S dummy;
pure int fun(int x)
{
    return dummy.x + x;
}

This code fails to compile:

Error: pure function onlineapp.fun cannot access mutable static data dummy

However, there is no mutable data to talk about in the first place so the code
should pass compilation.

The technique of using static data for a zero-sized struct is frequently used
in the allocator framework.

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