[lldb/DWARF] Unique enums parsed from declarations

This is a regression from llvm#96484 caught by @ZequanWu.

Note that we will still create separate enum types for types parsed from
two definitions. This is different from how we handle classes, but it is
not a regression.

I'm also adding the DieToType check to the class type parsing code,
although in this case, the type uniqueness should be enforced by the
UniqueDWARFASTType map.

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp

@@ -870,6 +870,13 @@ TypeSP DWARFASTParserClang::ParseEnum(const SymbolContext &sc,
     }
   }
   if (def_die) {
+    if (auto [it, inserted] = dwarf->GetDIEToType().try_emplace(
+            def_die.GetDIE(), DIE_IS_BEING_PARSED);
+        !inserted) {
+      if (it->getSecond() == nullptr || it->getSecond() == DIE_IS_BEING_PARSED)
+        return nullptr;
+      return it->getSecond()->shared_from_this();
+    }
     attrs = ParsedDWARFTypeAttributes(def_die);
   } else {
     // No definition found. Proceed with the declaration die. We can use it to
@@ -1798,6 +1805,13 @@ DWARFASTParserClang::ParseStructureLikeDIE(const SymbolContext &sc,
   }
 
   if (def_die) {
+    if (auto [it, inserted] = dwarf->GetDIEToType().try_emplace(
+            def_die.GetDIE(), DIE_IS_BEING_PARSED);
+        !inserted) {
+      if (it->getSecond() == nullptr || it->getSecond() == DIE_IS_BEING_PARSED)
+        return nullptr;
+      return it->getSecond()->shared_from_this();
+    }
     attrs = ParsedDWARFTypeAttributes(def_die);
   } else {
     // No definition found. Proceed with the declaration die. We can use it to

lldb/test/Shell/SymbolFile/DWARF/enum-declaration-uniqueness.cpp

@@ -0,0 +1,32 @@
+// RUN: %clangxx_host -gdwarf -c -o %t_a.o %s -DFILE_A
+// RUN: %clangxx_host -gdwarf -c -o %t_b.o %s -DFILE_B
+// RUN: %clangxx_host -o %t %t_a.o %t_b.o
+// RUN: %lldb %t \
+// RUN:   -o "target variable my_enum my_enum_ref" -o "image dump ast" \
+// RUN:   -o exit | FileCheck %s
+
+
+// CHECK: (lldb) target variable
+// CHECK: (MyEnum) my_enum = MyEnum_A
+// CHECK: (MyEnum &) my_enum_ref =
+// CHECK-SAME: &::my_enum_ref = MyEnum_A
+
+// CHECK: (lldb) image dump ast
+// CHECK: EnumDecl {{.*}} MyEnum
+// CHECK-NEXT: EnumConstantDecl {{.*}} MyEnum_A 'MyEnum'
+// CHECK-NOT: MyEnum
+
+enum MyEnum : int;
+
+extern MyEnum my_enum;
+
+#ifdef FILE_A
+enum MyEnum : int { MyEnum_A };
+
+MyEnum my_enum = MyEnum_A;
+
+int main() {}
+#endif
+#ifdef FILE_B
+MyEnum &my_enum_ref = my_enum;
+#endif