Comment # 3 on bug 1153314 from Tom de Vries

(In reply to Federico Mena Quintero from comment #2)
> So... the failure is with the LLVM7 included in rustc?
> 

AFAIU, in all cases I looked at, the system LLVM is used. [ FWIW, the version
bundled with the 1.32.0 tarball in openSUSE:Leap:15.1:rust is already LLVM8. ]

> And it works when we use the system's LLVM8?

I dug a bit further, and found the following code change:
...
$ git diff 1.32.0 1.33.0 -- librustc_codegen_llvm/debuginfo/metadata.rs
@@ -1173,7 +1164,10 @@ fn use_enum_fallback(cx: &CodegenCx) -> bool {
     // On MSVC we have to use the fallback mode, because LLVM doesn't
     // lower variant parts to PDB.
     return cx.sess().target.target.options.is_like_msvc
-        || llvm_util::get_major_version() < 7;
+        // LLVM version 7 did not release with an important bug fix;
+        // but the required patch is in the LLVM 8.  Rust LLVM reports
+        // 8 as well.
+        || llvm_util::get_major_version() < 8;
 }

 // Describes the members of an enum value: An enum is described as a union of
...

So, we have:

1. openSUSE Leap 15.1 without update repository:
   - rustc version 1.32.0
   - system llvm 7
2. openSUSE Leap 15.1 with update repository:
   - rustc version 1.36.0
   - system llvm 7
3. openSUSE Tumbleweed:
   - rustc version 1.37.0
   - system llvm 8

In case 1, use_enum_fallback returns false, because llvm version is 7 (required
to be at least 7 to avoid fallback). So the fallback is not used, the compiler
generates a DW_TAG_variant description of the enum, and the correct value is
printed.

In case 2, use_enum_fallback returns true, because llvm version is 7 (required
to be at least 8 to avoid fallback). So the fallback is used, the compiler
generates a legacy description of the enum, which contains a bug, and the
incorrect value is printed.

In case 3, use_enum_fallback returns true, because llvm version is 8 (required
to be at least 8 to avoid fallback). So the fallback is not used, and things
are back to how they were at case 1.