[Issue 20848] New: Bug in Nullable?

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20848

          Issue ID: 20848
           Summary: Bug in Nullable?
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: porton at narod.ru

Apaprently I found a bug in `Nullable`:

https://github.com/vporton/nullable-mofile-bug

///////////////////
import std.typecons;
import mofile;

Nullable!MoFile mo;
///////////////////

/snap/dmd/102/bin/../import/phobos/std/format.d(3217,9): Error: static assert: 
"immutable(void)[] must be an InputRange"
/snap/dmd/102/bin/../import/phobos/std/format.d(1875,20):        instantiated
from here: formatValueImpl!(Appender!string, immutable(void)[], char)
/snap/dmd/102/bin/../import/phobos/std/format.d(3749,16):        instantiated
from here: formatValue!(Appender!string, immutable(void)[], char)
/snap/dmd/102/bin/../import/phobos/std/format.d(4451,30):        instantiated
from here: formatElement!(Appender!string, immutable(void)[], char)
/snap/dmd/102/bin/../import/phobos/std/format.d(1875,20):        ... (2
instantiations, -v to show) ...
/snap/dmd/102/bin/../import/phobos/std/typecons.d(2791,17):        instantiated
from here: toString!(Appender!string)
source/test.d(4,1):        instantiated from here: Nullable!(MoFile)
dmd failed with exit code 1.

$ dmd --version
DMD64 D Compiler v2.090.1
Copyright (C) 1999-2019 by The D Language Foundation, All Rights Reserved
written by Walter Bright

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