Fix Issue 21828 - Using enum of struct (containing another enum) before its declaration fails

[RazvanN7]

This is blocking: dlang/phobos#7766

[dlang-bot]

Thanks for your pull request and interest in making D better, @RazvanN7! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21828	normal	Using enum of struct (containing another enum) before its declaration fails

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#12437"

[BorisCarvajal]

@RazvanN7: you beat me for 5 minutes, I was about to pull my version. Still going to do it because I resolved in another way.

[MoonlightSentinel]

This adds an odd special case, #12438 seems to be the more general approach.

[RazvanN7]

I admit that doing semantic here isn't ideal, however, I think it's better to analyze the enum in its entirety. In contrast #12438 does semantic on the first member only and defers the rest for later.

That being said, I have no problem conceding as long as the issue is fixed.

[BorisCarvajal]

I admit that doing semantic here isn't ideal, however, I think it's better to analyze the enum in its entirety. In contrast #12438 does semantic on the first member only and defers the rest for later.

Why? the spec says clearly

• If the EnumBaseType is not explicitly set, and the first EnumMember has an AssignExpression, it is set to the type of that AssignExpression. Otherwise, it defaults to type int.

[MoonlightSentinel]

A self-contained solution as a compromise of both PR's:

diff --git a/src/dmd/denum.d b/src/dmd/denum.d
index 267fb4f01..9886d85dc 100644
--- a/src/dmd/denum.d
+++ b/src/dmd/denum.d
@@ -342,6 +342,8 @@ extern (C++) final class EnumDeclaration : ScopeDsymbol
                 Loc locx = loc.isValid() ? loc : this.loc;
                 memtype = memtype.typeSemantic(locx, _scope);
             }
+            else
+                dsymbolSemantic(this, _scope);
         }
         if (!memtype)
         {

Allthough this is slightly less capable w.r.t. to deep forward references.