[llvm-bugs] [Bug 40100] New: [CodeView] clang emits an incorrect LF_NESTTYPE record for unnamed enums.

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40100

            Bug ID: 40100
           Summary: [CodeView] clang emits an incorrect LF_NESTTYPE record
                    for unnamed enums.
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: zturner at google.com
                CC: jdevlieghere at apple.com, keith.walker at arm.com,
                    llvm-bugs at lists.llvm.org,
                    paul_robinson at playstation.sony.com, rnk at google.com,
                    zturner at google.com

Consider this code:

struct SS {
  constexpr SS() {}
  struct {
    int X = 3;
  } UnnamedStructInstance;
  enum {
    Enumerator1 = 0,
    Enumerator2 = 1
  } UnnamedEnumInstance = Enumerator1;
  union {
    int A = 0;
    short B;
  } UnnamedUnionInstance;
};

If we build this with clang and lld-link, then run `llvm-pdbutil dump -types`
on it, the relevant CodeView records that we emit will look like this:

  0x1028 | LF_STRUCTURE [size = 112] `SS::<unnamed-type-UnnamedStructInstance>`
           unique name: `.?AU<unnamed-type-UnnamedStructInstance>@SS@@`
           vtable: <no type>, base list: <no type>, field list: <no type>
           options: forward ref (-> 0x1032) | has unique name | is nested,
sizeof 0
  0x102A | LF_ENUM [size = 80] `SS::<unnamed-tag>`
           unique name: `.?AW4<unnamed-type-UnnamedEnumInstance>@SS@@`
           field list: 0x1029, underlying type: 0x0074 (int)
           options: has unique name | is nested
  0x102B | LF_UNION [size = 100] `SS::<unnamed-type-UnnamedUnionInstance>`
           unique name: `.?AT<unnamed-type-UnnamedUnionInstance>@SS@@`
           field list: <no type>
           options: forward ref (-> 0x1034) | has unique name | is nested,
sizeof 0
  0x102F | LF_FIELDLIST [size = 216]
           - LF_MEMBER [name = `UnnamedStructInstance`, Type = 0x1028, offset =
0, attrs = public]
           - LF_MEMBER [name = `UnnamedEnumInstance`, Type = 0x102A, offset =
4, attrs = public]
           - LF_MEMBER [name = `UnnamedUnionInstance`, Type = 0x102B, offset =
8, attrs = public]
           - LF_ONEMETHOD [name = `SS`]
             type = 0x102E, vftable offset = -1, attrs = public
           - LF_NESTTYPE [name = `<unnamed-type-UnnamedStructInstance>`, parent
= 0x1028]
           - LF_NESTTYPE [name = ``, parent = 0x102A]
           - LF_NESTTYPE [name = `<unnamed-type-UnnamedUnionInstance>`, parent
= 0x102B]


Note that we've correctly emitted an LF_STRUCTURE, LF_ENUM, and LF_UNION with
names and unique names that include the "<unnamed-type-" prefix.

However, in the LF_FIELDLIST only the LF_NESTTYPES for the structure and enum
have the name field set.  The one that points to the LF_ENUM has an empty name.
 It should say <unnamed-type-UnnamedEnumInstance>.

This prevents LLDB from building a proper AST for these nested unnamed enums.

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