[Issue 20076] New: [2.087.0] structs won't copy when using alias this and being assigned a const instance of said struct

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20076

          Issue ID: 20076
           Summary: [2.087.0] structs won't copy when using alias this and
                    being assigned a const instance of said struct
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Windows
            Status: NEW
          Severity: blocker
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: gooberman at gmail.com

Created attachment 1756
  --> https://issues.dlang.org/attachment.cgi?id=1756&action=edit
Code example.  The last two lines should be functionally identical to the prior
two lines. Currently they error; and as long as alias this resolves they won't
give the correct output...

Assigning a T to a const( T ) results in a proper struct copy.

Assigning a const( T ) to a T results in alias this resolving on const( T ) and
tries to construct T with it.

This is quite whack, and resolving alias this in that manner breaks a lot of
assumptions in my code about how copying structs is meant to work.

Haven't been able to work around it with opAssign yet.

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