[Issue 23686] template instance reused with default alias arg

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23686

--- Comment #2 from Dlang Bot <dlang-bot at dlang.rocks> ---
@SixthDot updated dlang/dmd pull request #15681 "fix issue 23865 - ICE on
attempt to insert an non overloadable symbol…" fixing this issue:

- fix issue 23686 - TemplateAliasParam default value possibly considered equal
in different instances (#15679)

  The default arg might depend on another TemplateParameter,
  in which case it is required to copy the AST, otherwise
  different instances of the template might be falsy considered equal.

https://github.com/dlang/dmd/pull/15681

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