[NFC] Refactor `GetDWARFDeclContext` to return `DWARFDeclContext`

[jankratochvil]

Summary

In D70646 I broke http://lab.llvm.org:8080/green/view/LLDB/job/lldb-cmake/7400/ so this is a second attempt.
Unfortunately I do not have reproducible the breakage of Green Dragon locally.
The bug was that DWARFDebugInfoEntry::GetDWARFDeclContext reversed order of the items, that is fixed now.
OK for check-in? It is no longer so pretty but still worth it IMO.

[labath]

Yes, I agree this is better.

One way to this could be improved further is to change the recursion in GetDWARFDeclContext into a loop (then you wouldn't need the extra wrapper).

[jankratochvil]

In D73787#1859754, @labath wrote:

One way to this could be improved further is to change the recursion in GetDWARFDeclContext into a loop (then you wouldn't need the extra wrapper).

True, I am stupid. But then I find there a need for the static method (as having this and iterating die pointer is error-prone).

[labath]

This looks good too.

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

TypeSP DWARFASTParserClang::ParseEnum(const SymbolContext &sc,
   const dw_tag_t tag = die.Tag();
   TypeSP type_sp;
 
   if (attrs.is_forward_declaration) {
     type_sp = ParseTypeFromClangModule(sc, die, log);
     if (type_sp)
       return type_sp;
 
-    DWARFDeclContext die_decl_ctx;
-    SymbolFileDWARF::GetDWARFDeclContext(die, die_decl_ctx);
+    DWARFDeclContext die_decl_ctx = SymbolFileDWARF::GetDWARFDeclContext(die);
 
     type_sp = dwarf->FindDefinitionTypeForDWARFDeclContext(die_decl_ctx);
 
     if (!type_sp) {
       SymbolFileDWARFDebugMap *debug_map_symfile = dwarf->GetDebugMapSymfile();
       if (debug_map_symfile) {
         // We weren't able to find a full declaration in this DWARF,
         // see if we have a declaration anywhere else...
if (attrs.is_forward_declaration) {
     }
 
     // See if the type comes from a Clang module and if so, track down
     // that type.
     type_sp = ParseTypeFromClangModule(sc, die, log);
     if (type_sp)
       return type_sp;
 
-    DWARFDeclContext die_decl_ctx;
-    SymbolFileDWARF::GetDWARFDeclContext(die, die_decl_ctx);
+    DWARFDeclContext die_decl_ctx = SymbolFileDWARF::GetDWARFDeclContext(die);
 
     // type_sp = FindDefinitionTypeForDIE (dwarf_cu, die,
     // type_name_const_str);
     type_sp = dwarf->FindDefinitionTypeForDWARFDeclContext(die_decl_ctx);
 
     if (!type_sp) {
       SymbolFileDWARFDebugMap *debug_map_symfile = dwarf->GetDebugMapSymfile();
       if (debug_map_symfile) {
if (func_range.GetBaseAddress().IsValid()) {
         // demangled name using the decl context. We skip if the function is
         // "main" as its name is never mangled.
         bool is_static = false;
         bool is_variadic = false;
         bool has_template_params = false;
         unsigned type_quals = 0;
         std::vector<CompilerType> param_types;
         std::vector<clang::ParmVarDecl *> param_decls;
-        DWARFDeclContext decl_ctx;
         StreamString sstr;
 
-        SymbolFileDWARF::GetDWARFDeclContext(die, decl_ctx);
+        DWARFDeclContext decl_ctx = SymbolFileDWARF::GetDWARFDeclContext(die);
         sstr << decl_ctx.GetQualifiedName();
 
         clang::DeclContext *containing_decl_ctx =
             GetClangDeclContextContainingDIE(die, nullptr);
         ParseChildParameters(containing_decl_ctx, die, true, is_static,
                              is_variadic, has_template_params, param_types,
                              param_decls, type_quals);
         sstr << "(";

lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.h

public:
   // be the next entry in the list...
   DWARFDebugInfoEntry *GetFirstChild() {
     return HasChildren() ? this + 1 : nullptr;
   }
   const DWARFDebugInfoEntry *GetFirstChild() const {
     return HasChildren() ? this + 1 : nullptr;
   }
 
-  void GetDWARFDeclContext(DWARFUnit *cu,
-                           DWARFDeclContext &dwarf_decl_ctx) const;
+  DWARFDeclContext GetDWARFDeclContext(DWARFUnit *cu) const;
 
   DWARFDIE GetParentDeclContextDIE(DWARFUnit *cu) const;
   DWARFDIE GetParentDeclContextDIE(DWARFUnit *cu,
                                    const DWARFAttributes &attributes) const;
 
   void SetSiblingIndex(uint32_t idx) { m_sibling_idx = idx; }
   void SetParentIndex(uint32_t idx) { m_parent_idx = idx; }
 
 protected:
+  void DWARFDebugInfoEntry::GetDWARFDeclContext(
+      DWARFUnit *cu, DWARFDeclContext &dwarf_decl_ctx) const;
+
   dw_offset_t m_offset; // Offset within the .debug_info/.debug_types
   uint32_t m_parent_idx; // How many to subtract from "this" to get the parent.
                          // If zero this die has no parent
   uint32_t m_sibling_idx : 31, // How many to add to "this" to get the sibling.
       // If it is zero, then the DIE doesn't have children, or the
       // DWARF claimed it had children but the DIE only contained
       // a single NULL terminating child.
       m_has_children : 1;
   uint16_t m_abbr_idx;
   /// A copy of the DW_TAG value so we don't have to go through the compile
   /// unit abbrev table
   dw_tag_t m_tag = llvm::dwarf::DW_TAG_null;
 };
 
 #endif // SymbolFileDWARF_DWARFDebugInfoEntry_h_

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

void DWARFDebugInfoEntry::GetDWARFDeclContext(
   if (parent_decl_ctx_die && parent_decl_ctx_die.GetDIE() != this) {
     if (parent_decl_ctx_die.Tag() != DW_TAG_compile_unit &&
         parent_decl_ctx_die.Tag() != DW_TAG_partial_unit)
       parent_decl_ctx_die.GetDIE()->GetDWARFDeclContext(
           parent_decl_ctx_die.GetCU(), dwarf_decl_ctx);
   }
 }
 
+DWARFDeclContext DWARFDebugInfoEntry::GetDWARFDeclContext(DWARFUnit *cu) const {
+  DWARFDeclContext dwarf_decl_ctx;
+  GetDWARFDeclContext(cu, dwarf_decl_ctx);
+  return dwarf_decl_ctx;
+}
+
 DWARFDIE
 DWARFDebugInfoEntry::GetParentDeclContextDIE(DWARFUnit *cu) const {
   DWARFAttributes attributes;
   GetAttributes(cu, attributes);
   return GetParentDeclContextDIE(cu, attributes);
 }
 
 DWARFDIE

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h

public:
 
   static lldb_private::CompilerDecl GetDecl(const DWARFDIE &die);
 
   static lldb_private::CompilerDeclContext GetDeclContext(const DWARFDIE &die);
 
   static lldb_private::CompilerDeclContext
   GetContainingDeclContext(const DWARFDIE &die);
 
-  static void GetDWARFDeclContext(const DWARFDIE &die,
-                                  DWARFDeclContext &dwarf_decl_ctx);
+  static DWARFDeclContext GetDWARFDeclContext(const DWARFDIE &die);
 
   static lldb::LanguageType LanguageTypeFromDWARF(uint64_t val);
 
   static lldb::LanguageType GetLanguage(DWARFUnit &unit);
 
 protected:
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *, lldb_private::Type *>
       DIEToTypePtr;

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

if (type_name) {
               default:
                 // Tags don't match, don't event try to resolve using this type
                 // whose name matches....
                 break;
               }
             }
 
             if (try_resolving_type) {
-              DWARFDeclContext type_dwarf_decl_ctx;
-              GetDWARFDeclContext(type_die, type_dwarf_decl_ctx);
+              DWARFDeclContext type_dwarf_decl_ctx =
+                  GetDWARFDeclContext(type_die);
 
               if (log) {
                 GetObjectFile()->GetModule()->LogMessage(
                     log,
                     "SymbolFileDWARF::"
                     "FindDefinitionTypeForDWARFDeclContext(tag=%s, "
                     "qualified-name='%s') trying die=0x%8.8x (%s)",
                     DW_TAG_value_to_name(dwarf_decl_ctx[0].tag),
if (num_attributes > 0) {
         // declared in a namespace B which in turn is contained in a
         // namespace A, the command "frame var j" returns
         //   "(int) A::B::j = 4".
         // If the compiler does not emit a linkage name, we should be
         // able to generate a fully qualified name from the
         // declaration context.
         if ((parent_tag == DW_TAG_compile_unit ||
              parent_tag == DW_TAG_partial_unit) &&
-            Language::LanguageIsCPlusPlus(GetLanguage(*die.GetCU()))) {
-          DWARFDeclContext decl_ctx;
-
-          GetDWARFDeclContext(die, decl_ctx);
-          mangled = decl_ctx.GetQualifiedNameAsConstString().GetCString();
-        }
+            Language::LanguageIsCPlusPlus(GetLanguage(*die.GetCU())))
+          mangled = GetDWARFDeclContext(die)
+                        .GetQualifiedNameAsConstString()
+                        .GetCString();
       }
 
       if (tag == DW_TAG_formal_parameter)
         scope = eValueTypeVariableArgument;
       else {
         // DWARF doesn't specify if a DW_TAG_variable is a local, global
         // or static variable, so we have to do a little digging:
         // 1) DW_AT_linkage_name implies static lifetime (but may be missing)

 
 CompilerDeclContext
 SymbolFileDWARF::GetContainingDeclContext(const DWARFDIE &die) {
   if (DWARFASTParser *dwarf_ast = GetDWARFParser(*die.GetCU()))
     return dwarf_ast->GetDeclContextContainingUIDFromDWARF(die);
   return CompilerDeclContext();
 }
 
-void SymbolFileDWARF::GetDWARFDeclContext(const DWARFDIE &die,
-                                          DWARFDeclContext &dwarf_decl_ctx) {
-  if (!die.IsValid()) {
-    dwarf_decl_ctx.Clear();
-    return;
-  }
+DWARFDeclContext SymbolFileDWARF::GetDWARFDeclContext(const DWARFDIE &die) {
+  if (!die.IsValid())
+    return {};
+  DWARFDeclContext dwarf_decl_ctx =
+      die.GetDIE()->GetDWARFDeclContext(die.GetCU());
   dwarf_decl_ctx.SetLanguage(GetLanguage(*die.GetCU()));
-  die.GetDIE()->GetDWARFDeclContext(die.GetCU(), dwarf_decl_ctx);
+  return dwarf_decl_ctx;
 }
 
 LanguageType SymbolFileDWARF::LanguageTypeFromDWARF(uint64_t val) {
   // Note: user languages between lo_user and hi_user must be handled
   // explicitly here.
   switch (val) {
   case DW_LANG_Mips_Assembler:
     return eLanguageTypeMipsAssembler;