https://issues.dlang.org/show_bug.cgi?id=21997

          Issue ID: 21997
           Summary: CTFE should allow function pointer casts with
                    different attributes
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: moonlightsentinel@disroot.org

The following works at runtime but is rejected during CTFE:

int nonPureFunc(int i)
{
    return 2 * i;
}

void main()
{
    auto pureFunc = cast(int function(int) pure) &nonPureFunc;
    assert(pureFunc(2) == 4);
}

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