[lldb][DWARFASTParserClang] Complete and make use of LLVM's RTTI support (llvm#170249)

We almost had RTTI support for `DWARFASTParserClang`, but because
`classof` was protected, using `llvm::cast`/etc. on it would fail to
compile with:
```
llvm/include/llvm/Support/Casting.h:64:57: error: 'classof' is a protected member of 'DWARFASTParserClang'
   64 |   static inline bool doit(const From &Val) { return To::classof(&Val); }
      |                                                         ^
llvm/include/llvm/Support/Casting.h:110:32: note: in instantiation of member function 'llvm::isa_impl<DWARFASTParserClang, lldb_private::plugin::dwarf::DWARFASTParser>::doit' requested here
  110 |     return isa_impl<To, From>::doit(*Val);
```

This patch makes `classof` public and turns `static_cast`s of
`DWARFASTParserClang` into `llvm::cast`s.

(cherry picked from commit ac19d38)

Author: Michael137

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

@@ -3848,12 +3848,10 @@ bool DWARFASTParserClang::CopyUniqueClassMethodTypes(
     }
   }
 
-  DWARFASTParserClang *src_dwarf_ast_parser =
-      static_cast<DWARFASTParserClang *>(
-          SymbolFileDWARF::GetDWARFParser(*src_class_die.GetCU()));
-  DWARFASTParserClang *dst_dwarf_ast_parser =
-      static_cast<DWARFASTParserClang *>(
-          SymbolFileDWARF::GetDWARFParser(*dst_class_die.GetCU()));
+  auto *src_dwarf_ast_parser = llvm::cast<DWARFASTParserClang>(
+      SymbolFileDWARF::GetDWARFParser(*src_class_die.GetCU()));
+  auto *dst_dwarf_ast_parser = llvm::cast<DWARFASTParserClang>(
+      SymbolFileDWARF::GetDWARFParser(*dst_class_die.GetCU()));
   auto link = [&](DWARFDIE src, DWARFDIE dst) {
     auto &die_to_type = dst_class_die.GetDWARF()->GetDIEToType();
     clang::DeclContext *dst_decl_ctx =

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

@@ -47,6 +47,11 @@ class DWARFASTParserClang : public lldb_private::plugin::dwarf::DWARFASTParser {
 
   ~DWARFASTParserClang() override;
 
+  // LLVM RTTI support
+  static bool classof(const DWARFASTParser *Parser) {
+    return Parser->GetKind() == Kind::DWARFASTParserClang;
+  }
+
   // DWARFASTParser interface.
   lldb::TypeSP
   ParseTypeFromDWARF(const lldb_private::SymbolContext &sc,
@@ -276,10 +281,6 @@ class DWARFASTParserClang : public lldb_private::plugin::dwarf::DWARFASTParser {
   lldb::ModuleSP
   GetModuleForType(const lldb_private::plugin::dwarf::DWARFDIE &die);
 
-  static bool classof(const DWARFASTParser *Parser) {
-    return Parser->GetKind() == Kind::DWARFASTParserClang;
-  }
-
 private:
   struct FieldInfo {
     /// Size in bits that this field occupies. Can but

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

@@ -1573,17 +1573,17 @@ bool SymbolFileDWARF::HasForwardDeclForCompilerType(
   auto clang_type_system = compiler_type.GetTypeSystem<TypeSystemClang>();
   if (!clang_type_system)
     return false;
-  DWARFASTParserClang *ast_parser =
-      static_cast<DWARFASTParserClang *>(clang_type_system->GetDWARFParser());
+  auto *ast_parser =
+      llvm::cast<DWARFASTParserClang>(clang_type_system->GetDWARFParser());
   return ast_parser->GetClangASTImporter().CanImport(compiler_type);
 }
 
 bool SymbolFileDWARF::CompleteType(CompilerType &compiler_type) {
   std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
   auto clang_type_system = compiler_type.GetTypeSystem<TypeSystemClang>();
   if (clang_type_system) {
-    DWARFASTParserClang *ast_parser =
-        static_cast<DWARFASTParserClang *>(clang_type_system->GetDWARFParser());
+    auto *ast_parser =
+        llvm::cast<DWARFASTParserClang>(clang_type_system->GetDWARFParser());
     if (ast_parser &&
         ast_parser->GetClangASTImporter().CanImport(compiler_type))
       return ast_parser->GetClangASTImporter().CompleteType(compiler_type);
@@ -1627,8 +1627,7 @@ bool SymbolFileDWARF::CompleteType(CompilerType &compiler_type) {
 
   if (decl_die != def_die) {
     GetDIEToType()[def_die.GetDIE()] = type;
-    DWARFASTParserClang *ast_parser =
-        static_cast<DWARFASTParserClang *>(dwarf_ast);
+    auto *ast_parser = llvm::cast<DWARFASTParserClang>(dwarf_ast);
     ast_parser->MapDeclDIEToDefDIE(decl_die, def_die);
   }
 

lldb/unittests/Symbol/TestClangASTImporter.cpp

@@ -287,7 +287,7 @@ TEST_F(TestClangASTImporter, RecordLayoutFromOrigin) {
   clang_utils::SourceASTWithRecord source;
 
   auto *dwarf_parser =
-      static_cast<DWARFASTParserClang *>(source.ast->GetDWARFParser());
+      llvm::cast<DWARFASTParserClang>(source.ast->GetDWARFParser());
   auto &importer = dwarf_parser->GetClangASTImporter();
 
   // Set the layout for the origin decl in the origin ClangASTImporter.

lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp

@@ -1223,7 +1223,7 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ExplicitObjectParameter) {
   ASSERT_TRUE(static_cast<bool>(ts_or_err));
   llvm::consumeError(ts_or_err.takeError());
   auto *parser =
-      static_cast<DWARFASTParserClang *>((*ts_or_err)->GetDWARFParser());
+      llvm::cast<DWARFASTParserClang>((*ts_or_err)->GetDWARFParser());
 
   auto context_die = cu_die.GetFirstChild();
   ASSERT_TRUE(context_die.IsValid());
@@ -1400,7 +1400,7 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ParameterCreation) {
   llvm::consumeError(ts_or_err.takeError());
 
   auto *ts = static_cast<TypeSystemClang *>(ts_or_err->get());
-  auto *parser = static_cast<DWARFASTParserClang *>(ts->GetDWARFParser());
+  auto *parser = llvm::cast<DWARFASTParserClang>(ts->GetDWARFParser());
 
   auto subprogram = cu_die.GetFirstChild();
   ASSERT_TRUE(subprogram.IsValid());