[Issue 21646] New: Speculative recursive reference to struct with semantic error prints "error: unknown"

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21646

          Issue ID: 21646
           Summary: Speculative recursive reference to struct with
                    semantic error prints "error: unknown"
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: default_357-line at yahoo.de

struct Type {
  enum a = __traits(compiles, Type());
  static if (int(Type)) { }
}

Outputs: Error: unknown, please file report on issues.dlang.org on master of
2021-02-19.

<@CyberShadow> Introduced in https://github.com/dlang/dmd/pull/2786 apparently
<@CyberShadow> Before then it showed an appropriate error message

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