[Issue 22139] New: Compiler special cases object.dup when compiling with -preview=dip1000

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22139

          Issue ID: 22139
           Summary: Compiler special cases object.dup when compiling with
                    -preview=dip1000
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: moonlightsentinel at disroot.org

...as a workaround because it apparently breaks purity inference. This is
problematic because it indicates that custom implementations will most likely
be broken because they don't receive special treatment.

See
https://github.com/dlang/dmd/blob/3a9c2891b1f5bd650c42c2e623fbc3340d4d84f6/src/dmd/dcast.d#L855-L870

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