[lldb][DWARFASTParserClang] Treat DW_TAG_template_alias like we do DW_TAG_typedef #170135

Michael137 · 2025-12-01T13:31:51Z

Depends on:

[lldb][test] DWARFASTParserClangTests: extract test setup into helper structure #170132

Clang gained the -gtemplate-alias not too long ago, which emits C++ alias templates as DW_TAG_template_alias (instead of DW_TAG_typedef). The main difference is that DW_TAG_template_alias has DW_TAG_template_XXX children. The flag was not enabled by default because consumers (mainly LLDB) didn't know how to handle it. This patch adds rudimentary support for debugging with DW_TAG_template_alias.

This patch simply creates the same kind of TypedefDecl as we do for DW_TAG_typedef. The more complete solution would be to create a TypeAliasTemplateDecl and associated TypeAliasDecl. But that would require DWARF to carry generic template information, but currently each DW_TAG_template_alias represents a concrete instantiation. We could probably hack up some working AST representation that includes the template parameters, but I currently don't see a compelling reason to. All we need is the DW_AT_name and the DW_AT_type that the typedef refers to.

rdar://137499401

llvmbot · 2025-12-01T13:32:26Z

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

Depends on:

[lldb][test] DWARFASTParserClangTests: extract test setup into helper structure #170132

Clang gained the -gtemplate-alias not too long ago, which emits C++ alias templates as DW_TAG_template_alias (instead of DW_TAG_typedef). The main difference is that DW_TAG_template_alias has DW_TAG_template_XXX children. The flag was not enabled by default because consumers (mainly LLDB) didn't know how to handle it. This patch adds rudimentary support for debugging with DW_TAG_template_alias.

This patch simply creates the same kind of TypedefDecl as we do for DW_TAG_typedef. The more complete solution would be to create a TypeAliasTemplateDecl and associated TypeAliasDecl. But that would require DWARF to carry generic template information, but currently each DW_TAG_template_alias represents a concrete instantiation. We could probably hack up some working AST representation that includes the template parameters, but I currently don't see a compelling reason to. All we need is the DW_AT_name and the DW_AT_type that the typedef refers to.

One compelling reason to support DW_TAG_template_alias is that with -gsimple-template-names, DW_TAG_typedefs for alias templates have their template parameters stripped from the DW_AT_name. With just a plain DW_TAG_typedef, LLDB has no way to reconstruct the full DW_AT_name. But since DW_TAG_template_alias can carry template parameter children, LLDB can reconstitute the name by concatenating the DW_AT_names of the child tags.

Patch is 24.25 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/170135.diff

2 Files Affected:

(modified) lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp (+3-1)
(modified) lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp (+211-182)

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
index 36aa49ac3de95..3d556aea7b183 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -623,6 +623,7 @@ TypeSP DWARFASTParserClang::ParseTypeFromDWARF(const SymbolContext &sc,
 
     switch (tag) {
     case DW_TAG_typedef:
+    case DW_TAG_template_alias:
     case DW_TAG_base_type:
     case DW_TAG_pointer_type:
     case DW_TAG_reference_type:
@@ -748,7 +749,7 @@ DWARFASTParserClang::ParseTypeModifier(const SymbolContext &sc,
   TypeSP type_sp;
   CompilerType clang_type;
 
-  if (tag == DW_TAG_typedef) {
+  if (tag == DW_TAG_typedef || tag == DW_TAG_template_alias) {
     // DeclContext will be populated when the clang type is materialized in
     // Type::ResolveCompilerType.
     PrepareContextToReceiveMembers(
@@ -836,6 +837,7 @@ DWARFASTParserClang::ParseTypeModifier(const SymbolContext &sc,
     encoding_data_type = Type::eEncodingIsRValueReferenceUID;
     break;
   case DW_TAG_typedef:
+  case DW_TAG_template_alias:
     encoding_data_type = Type::eEncodingIsTypedefUID;
     break;
   case DW_TAG_const_type:
diff --git a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
index cef3a25a4a960..9e2722d53cc6d 100644
--- a/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
+++ b/lldb/unittests/SymbolFile/DWARF/DWARFASTParserClangTests.cpp
@@ -12,6 +12,7 @@
 #include "TestingSupport/Symbol/ClangTestUtils.h"
 #include "TestingSupport/Symbol/YAMLModuleTester.h"
 #include "lldb/Core/Debugger.h"
+#include "lldb/Symbol/Type.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
@@ -42,6 +43,46 @@ class DWARFASTParserClangStub : public DWARFASTParserClang {
     return keys;
   }
 };
+
+/// Helper structure for DWARFASTParserClang tests that want to parse DWARF
+/// generated using yaml2obj. On construction parses the supplied YAML data
+/// into a DWARF module and creates a DWARFASTParserClang and TypeSystem that
+/// live for the duration of this object.
+class DWARFASTParserClangYAMLTester {
+public:
+  DWARFASTParserClangYAMLTester(llvm::StringRef yaml_data)
+      : m_module_tester(yaml_data),
+        m_ast_holder_up(
+            std::make_unique<clang_utils::TypeSystemClangHolder>("ast")),
+        m_stub(*m_ast_holder_up->GetAST()) {}
+
+  DWARFDIE GetCUDIE() {
+    DWARFUnit *unit = m_module_tester.GetDwarfUnit();
+    assert(unit);
+
+    const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
+    assert(cu_entry->Tag() == DW_TAG_compile_unit);
+
+    return DWARFDIE(unit, cu_entry);
+  }
+
+  DWARFASTParserClangStub &GetParser() { return m_stub; }
+
+  TypeSystemClang &GetTypeSystem() {
+    assert(m_ast_holder_up);
+
+    TypeSystemClang *ts = m_ast_holder_up->GetAST();
+
+    assert(ts);
+
+    return *ts;
+  }
+
+private:
+  YAMLModuleTester m_module_tester;
+  std::unique_ptr<clang_utils::TypeSystemClangHolder> m_ast_holder_up;
+  DWARFASTParserClangStub m_stub;
+};
 } // namespace
 
 // If your implementation needs to dereference the dummy pointers we are
@@ -100,23 +141,15 @@ TEST_F(DWARFASTParserClangTests,
         - AbbrCode:        0x00000000
 )";
 
-  YAMLModuleTester t(yamldata);
-  ASSERT_TRUE((bool)t.GetDwarfUnit());
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFASTParserClangStub &ast_parser = tester.GetParser();
 
-  DWARFASTParserClangStub ast_parser(ast_ctx);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  const DWARFDebugInfoEntry *die_first = unit->DIE().GetDIE();
-  const DWARFDebugInfoEntry *die_child0 = die_first->GetFirstChild();
-  const DWARFDebugInfoEntry *die_child1 = die_child0->GetSibling();
-  const DWARFDebugInfoEntry *die_child2 = die_child1->GetSibling();
-  const DWARFDebugInfoEntry *die_child3 = die_child2->GetSibling();
-  std::vector<DWARFDIE> dies = {
-      DWARFDIE(unit, die_child0), DWARFDIE(unit, die_child1),
-      DWARFDIE(unit, die_child2), DWARFDIE(unit, die_child3)};
+  DWARFDIE die_first = tester.GetCUDIE();
+  DWARFDIE die_child0 = die_first.GetFirstChild();
+  DWARFDIE die_child1 = die_child0.GetSibling();
+  DWARFDIE die_child2 = die_child1.GetSibling();
+  DWARFDIE die_child3 = die_child2.GetSibling();
+  std::vector<DWARFDIE> dies = {die_child0, die_child1, die_child2, die_child3};
   std::vector<clang::DeclContext *> decl_ctxs = {
       (clang::DeclContext *)1LL, (clang::DeclContext *)2LL,
       (clang::DeclContext *)2LL, (clang::DeclContext *)3LL};
@@ -248,17 +281,9 @@ TEST_F(DWARFASTParserClangTests, TestCallingConventionParsing) {
         - AbbrCode:        0x0
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  DWARFDIE cu_die(unit, cu_entry);
+  DWARFASTParserClangYAMLTester tester(yamldata);
 
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   std::vector<std::string> found_function_types;
   // The DWARF above is just a list of functions. Parse all of them to
@@ -267,7 +292,8 @@ TEST_F(DWARFASTParserClangTests, TestCallingConventionParsing) {
     ASSERT_EQ(func.Tag(), DW_TAG_subprogram);
     SymbolContext sc;
     bool new_type = false;
-    lldb::TypeSP type = ast_parser.ParseTypeFromDWARF(sc, func, &new_type);
+    lldb::TypeSP type =
+        tester.GetParser().ParseTypeFromDWARF(sc, func, &new_type);
     found_function_types.push_back(
         type->GetForwardCompilerType().GetTypeName().AsCString());
   }
@@ -394,18 +420,9 @@ TEST_F(DWARFASTParserClangTests, TestPtrAuthParsing) {
         - AbbrCode:        0x00 # end of child tags of 0x0c
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
 
+  DWARFDIE cu_die = tester.GetCUDIE();
   DWARFDIE ptrauth_variable = cu_die.GetFirstChild();
   ASSERT_EQ(ptrauth_variable.Tag(), DW_TAG_variable);
   DWARFDIE ptrauth_type =
@@ -415,7 +432,7 @@ TEST_F(DWARFASTParserClangTests, TestPtrAuthParsing) {
   SymbolContext sc;
   bool new_type = false;
   lldb::TypeSP type_sp =
-      ast_parser.ParseTypeFromDWARF(sc, ptrauth_type, &new_type);
+      tester.GetParser().ParseTypeFromDWARF(sc, ptrauth_type, &new_type);
   CompilerType compiler_type = type_sp->GetForwardCompilerType();
   ASSERT_EQ(compiler_type.GetPtrAuthKey(), 0U);
   ASSERT_EQ(compiler_type.GetPtrAuthAddressDiversity(), false);
@@ -554,24 +571,17 @@ TEST_F(DWARFASTParserClangTests, TestDefaultTemplateParamParsing) {
   auto BufferOrError = llvm::MemoryBuffer::getFile(
       GetInputFilePath("DW_AT_default_value-test.yaml"), /*IsText=*/true);
   ASSERT_TRUE(BufferOrError);
-  YAMLModuleTester t(BufferOrError.get()->getBuffer());
 
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(BufferOrError.get()->getBuffer());
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   llvm::SmallVector<lldb::TypeSP, 2> types;
   for (DWARFDIE die : cu_die.children()) {
     if (die.Tag() == DW_TAG_class_type) {
       SymbolContext sc;
       bool new_type = false;
-      types.push_back(ast_parser.ParseTypeFromDWARF(sc, die, &new_type));
+      types.push_back(
+          tester.GetParser().ParseTypeFromDWARF(sc, die, &new_type));
     }
   }
 
@@ -605,23 +615,14 @@ TEST_F(DWARFASTParserClangTests, TestSpecDeclExistsError) {
   auto BufferOrError = llvm::MemoryBuffer::getFile(
       GetInputFilePath("DW_AT_spec_decl_exists-test.yaml"), /*IsText=*/true);
   ASSERT_TRUE(BufferOrError);
-  YAMLModuleTester t(BufferOrError.get()->getBuffer());
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(BufferOrError.get()->getBuffer());
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   llvm::SmallVector<lldb::TypeSP, 2> specializations;
   for (DWARFDIE die : cu_die.children()) {
     SymbolContext sc;
     bool new_type = false;
-    auto type = ast_parser.ParseTypeFromDWARF(sc, die, &new_type);
+    auto type = tester.GetParser().ParseTypeFromDWARF(sc, die, &new_type);
     llvm::StringRef die_name = llvm::StringRef(die.GetName());
     if (die_name.starts_with("_Optional_payload")) {
       specializations.push_back(std::move(type));
@@ -730,18 +731,8 @@ TEST_F(DWARFASTParserClangTests, TestUniqueDWARFASTTypeMap_CppInsertMapFind) {
         - AbbrCode:        0x00 # end of child tags of 0x0c
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   DWARFDIE decl_die;
   DWARFDIE def_die;
@@ -762,6 +753,8 @@ TEST_F(DWARFASTParserClangTests, TestUniqueDWARFASTTypeMap_CppInsertMapFind) {
   ParsedDWARFTypeAttributes attrs(def_die);
   ASSERT_TRUE(attrs.decl.IsValid());
 
+  DWARFASTParserClangStub &ast_parser = tester.GetParser();
+
   SymbolContext sc;
   bool new_type = false;
   lldb::TypeSP type_sp = ast_parser.ParseTypeFromDWARF(sc, decl_die, &new_type);
@@ -906,18 +899,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer) {
         - AbbrCode: 0x0
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto context_die = cu_die.GetFirstChild();
   ASSERT_TRUE(context_die.IsValid());
@@ -932,7 +915,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer) {
     auto param_die = decl_die.GetFirstChild();
     ASSERT_TRUE(param_die.IsValid());
 
-    EXPECT_EQ(param_die, ast_parser.GetObjectParameter(decl_die, context_die));
+    EXPECT_EQ(param_die,
+              tester.GetParser().GetObjectParameter(decl_die, context_die));
   }
 
   {
@@ -945,8 +929,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer) {
     auto param_die = subprogram_definition.GetFirstChild();
     ASSERT_TRUE(param_die.IsValid());
 
-    EXPECT_EQ(param_die, ast_parser.GetObjectParameter(subprogram_definition,
-                                                       context_die));
+    EXPECT_EQ(param_die, tester.GetParser().GetObjectParameter(
+                             subprogram_definition, context_die));
   }
 }
 
@@ -1076,18 +1060,8 @@ TEST_F(DWARFASTParserClangTests,
         - AbbrCode: 0x0
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto context_die = cu_die.GetFirstChild();
   ASSERT_TRUE(context_die.IsValid());
@@ -1105,7 +1079,7 @@ TEST_F(DWARFASTParserClangTests,
   auto param_die = subprogram_definition.GetFirstChild();
   ASSERT_TRUE(param_die.IsValid());
   EXPECT_EQ(param_die,
-            ast_parser.GetObjectParameter(subprogram_definition, {}));
+            tester.GetParser().GetObjectParameter(subprogram_definition, {}));
 }
 
 TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ExplicitObjectParameter) {
@@ -1243,14 +1217,8 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ExplicitObjectParameter) {
         - AbbrCode: 0x0
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto ts_or_err =
       cu_die.GetDWARF()->GetTypeSystemForLanguage(eLanguageTypeC_plus_plus);
@@ -1419,22 +1387,8 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ParameterCreation) {
         - AbbrCode: 0x0
 ...
 )";
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto ts_or_err =
-      cu_die.GetDWARF()->GetTypeSystemForLanguage(eLanguageTypeC_plus_plus);
-  ASSERT_TRUE(static_cast<bool>(ts_or_err));
-  llvm::consumeError(ts_or_err.takeError());
-
-  auto *ts = static_cast<TypeSystemClang *>(ts_or_err->get());
-  auto *parser = static_cast<DWARFASTParserClang *>(ts->GetDWARFParser());
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto subprogram = cu_die.GetFirstChild();
   ASSERT_TRUE(subprogram.IsValid());
@@ -1442,11 +1396,13 @@ TEST_F(DWARFASTParserClangTests, TestParseSubroutine_ParameterCreation) {
 
   SymbolContext sc;
   bool new_type;
-  auto type_sp = parser->ParseTypeFromDWARF(sc, subprogram, &new_type);
+  auto type_sp =
+      tester.GetParser().ParseTypeFromDWARF(sc, subprogram, &new_type);
   ASSERT_NE(type_sp, nullptr);
 
-  auto result = ts->GetTranslationUnitDecl()->lookup(
-      clang_utils::getDeclarationName(*ts, "func"));
+  TypeSystemClang &ts = tester.GetTypeSystem();
+  auto result = ts.GetTranslationUnitDecl()->lookup(
+      clang_utils::getDeclarationName(ts, "func"));
   ASSERT_TRUE(result.isSingleResult());
 
   auto const *func = llvm::cast<clang::FunctionDecl>(result.front());
@@ -1609,19 +1565,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer_IndexEncoding) {
         - AbbrCode: 0x0
 ...
 )";
-
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto context_die = cu_die.GetFirstChild();
   ASSERT_TRUE(context_die.IsValid());
@@ -1640,7 +1585,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer_IndexEncoding) {
     auto param_die = sub1.GetFirstChild().GetSibling();
     ASSERT_TRUE(param_die.IsValid());
 
-    EXPECT_EQ(param_die, ast_parser.GetObjectParameter(sub1, context_die));
+    EXPECT_EQ(param_die,
+              tester.GetParser().GetObjectParameter(sub1, context_die));
   }
 
   // Object parameter is at constant index 0
@@ -1648,7 +1594,8 @@ TEST_F(DWARFASTParserClangTests, TestObjectPointer_IndexEncoding) {
     auto param_die = sub2.GetFirstChild();
     ASSERT_TRUE(param_die.IsValid());
 
-    EXPECT_EQ(param_die, ast_parser.GetObjectParameter(sub2, context_die));
+    EXPECT_EQ(param_die,
+              tester.GetParser().GetObjectParameter(sub2, context_die));
   }
 }
 
@@ -1711,19 +1658,8 @@ TEST_F(DWARFASTParserClangTests, TestTypeBitSize) {
             - Value: 0x02
 ...
 )";
-
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto type_die = cu_die.GetFirstChild();
   ASSERT_TRUE(type_die.IsValid());
@@ -1734,8 +1670,8 @@ TEST_F(DWARFASTParserClangTests, TestTypeBitSize) {
   EXPECT_EQ(attrs.data_bit_size.value_or(0), 2U);
 
   SymbolContext sc;
-  auto type_sp =
-      ast_parser.ParseTypeFromDWARF(sc, type_die, /*type_is_new_ptr=*/nullptr);
+  auto type_sp = tester.GetParser().ParseTypeFromDWARF(
+      sc, type_die, /*type_is_new_ptr=*/nullptr);
   ASSERT_NE(type_sp, nullptr);
 
   EXPECT_EQ(llvm::expectedToOptional(type_sp->GetByteSize(nullptr)).value_or(0),
@@ -1857,27 +1793,17 @@ TEST_F(DWARFASTParserClangTests, TestBitIntParsing) {
 ...
 
 )";
-
-  YAMLModuleTester t(yamldata);
-
-  DWARFUnit *unit = t.GetDwarfUnit();
-  ASSERT_NE(unit, nullptr);
-  const DWARFDebugInfoEntry *cu_entry = unit->DIE().GetDIE();
-  ASSERT_EQ(cu_entry->Tag(), DW_TAG_compile_unit);
-  ASSERT_EQ(unit->GetDWARFLanguageType(), DW_LANG_C_plus_plus);
-  DWARFDIE cu_die(unit, cu_entry);
-
-  auto holder = std::make_unique<clang_utils::TypeSystemClangHolder>("ast");
-  auto &ast_ctx = *holder->GetAST();
-  DWARFASTParserClangStub ast_parser(ast_ctx);
+  DWARFASTParserClangYAMLTester tester(yamldata);
+  DWARFDIE cu_die = tester.GetCUDIE();
 
   auto type_die = cu_die.GetFirstChild();
   ASSERT_TRUE(type_die.IsValid());
 
   {
     SymbolContext sc;
-    auto type_sp = ast_parser.ParseTypeFromDWARF(sc, type_die,
-                                                 /*type_is_new_ptr=*/nullptr);
+    auto type_sp =
+        tester.GetParser().ParseTypeFromDWARF(sc, type_die,
+                                              /*type_is_new_ptr=*/nullptr);
     ASSERT_NE(type_sp, nullptr);
 
     EXPECT_EQ(
@@ -1891,8 +1817,9 @@ TEST_F(DWARFASTParserClangTests, TestBitIntParsing) {
   {
     type_die = type_die.GetSibling();
     SymbolContext sc;
-    auto type_sp = ast_parser.ParseTypeFromDWARF(sc, type_die,
-                                                 /*type_is_new_ptr=*/nullptr);
+    auto type_sp =
+        tester.GetParser().ParseTypeFromDWARF(sc, type_die,
+                                              /*type_is_new_ptr=*/nullptr);
     ASSERT_NE(type_sp, nullptr);
 
     EXPECT_EQ(
@@ -1906,8 +1833,9 @@ TEST_F(DWARFASTParserClangTests, TestBitIntParsing) {
   {
     t...
[truncated]

dwblaikie · 2025-12-01T19:17:36Z

One compelling reason to support DW_TAG_template_alias is that with -gsimple-template-names, DW_TAG_typedefs for alias templates have their template parameters stripped from the DW_AT_name.

Is this true? https://godbolt.org/z/YEPE1fobE doesn't /look/ like it's true?

Michael137 · 2025-12-01T23:52:31Z

One compelling reason to support DW_TAG_template_alias is that with -gsimple-template-names, DW_TAG_typedefs for alias templates have their template parameters stripped from the DW_AT_name.

Is this true? https://godbolt.org/z/YEPE1fobE doesn't /look/ like it's true?

Oh maybe I'm misremembering, thought that's why Sony needed it. Let me check

Michael137 · 2025-12-02T00:49:15Z

One compelling reason to support DW_TAG_template_alias is that with -gsimple-template-names, DW_TAG_typedefs for alias templates have their template parameters stripped from the DW_AT_name.

Is this true? https://godbolt.org/z/YEPE1fobE doesn't /look/ like it's true?

Yea seems like i misremembered this, updated the description.

github-actions · 2025-12-02T07:06:05Z

✅ With the latest revision this PR passed the C/C++ code formatter.

OCHyams · 2025-12-02T15:40:14Z

One compelling reason to support DW_TAG_template_alias is that with -gsimple-template-names, DW_TAG_typedefs for alias templates have their template parameters stripped from the DW_AT_name.

Is this true? https://godbolt.org/z/YEPE1fobE doesn't /look/ like it's true?

Oh maybe I'm misremembering, thought that's why Sony needed it. Let me check

I think the reason we wanted to support template aliases was because the DW_TAG_typedefs don't have their template parameters stripped (which makes sense, because then you lose the template parameter information). The template aliases let us reconstruct the alias with parameters in the debugger, rather than just using the name string.

Ah here's more info from #54624:

We have a private dwarf extension to hint to dwarf consumers that a namespace should be hidden, and we noticed the namespace gets printed in template alias names when a type from the namespace is used as a template argument to an alias instantiation.

In terms of this pull request I am probably not best placed to review it as I'm not very familiar with the LLDB side of things. If it matters, IIRC there were a couple of edge cases where Clang falls back to using DW_AT_typdef (though maybe some of those have been fixed? (possibly by you? 😄 ) I think I recall seeing some movement in the area at some point).

… structure Depends on: * llvm#170249 We keep repeating the boilerplate of creating a `DWARFASTParserClangStub` and `TypeSystemClangHolder` in all the unit-test cases. Lets extract this into a helper to make the tests easier to grok.

…_TAG_typedef Depends on: * llvm#170132 Clang gained the `-gtemplate-alias` not too long ago, which emits C++ alias templates as `DW_TAG_template_alias` (instead of `DW_TAG_typedef`). The main difference is that `DW_TAG_template_alias` has `DW_TAG_template_XXX` children. The flag was not enabled by default because consumers (mainly LLDB) didn't know how to handle it. This patch adds rudimentary support for debugging with `DW_TAG_template_alias`. This patch simply creates the same kind of `TypedefDecl` as we do for `DW_TAG_typedef`. The more complete solution would be to create a `TypeAliasTemplateDecl` and associated `TypeAliasDecl`. But that would require DWARF to carry generic template information, but currently each `DW_TAG_template_alias` represents a concrete instantiation. We could probably hack up some working AST representation that includes the template parameters, but I currently don't see a compelling reason to. All we need is the `DW_AT_name` and the `DW_AT_type` that the typedef refers to. One compelling reason to support `DW_TAG_template_alias` is that with `-gsimple-template-names`, `DW_TAG_typedef`s for alias templates have their template parameters stripped from the `DW_AT_name`. With just a plain `DW_TAG_typedef`, LLDB has no way to reconstruct the full `DW_AT_name`. But since `DW_TAG_template_alias` can carry template parameter children, LLDB can reconstitute the name by concatenating the `DW_AT_name`s of the child tags.

Michael137 · 2025-12-03T02:49:16Z

Test failure unrelated:

NameError: name 'expectedFailureAll' is not defined

…_TAG_typedef (llvm#170135) Depends on: * llvm#170132 Clang gained the `-gtemplate-alias` not too long ago, which emits C++ alias templates as `DW_TAG_template_alias` (instead of `DW_TAG_typedef`). The main difference is that `DW_TAG_template_alias` has `DW_TAG_template_XXX` children. The flag was not enabled by default because consumers (mainly LLDB) didn't know how to handle it. This patch adds rudimentary support for debugging with `DW_TAG_template_alias`. This patch simply creates the same kind of `TypedefDecl` as we do for `DW_TAG_typedef`. The more complete solution would be to create a `TypeAliasTemplateDecl` and associated `TypeAliasDecl`. But that would require DWARF to carry generic template information, but currently each `DW_TAG_template_alias` represents a concrete instantiation. We could probably hack up some working AST representation that includes the template parameters, but I currently don't see a compelling reason to. All we need is the `DW_AT_name` and the `DW_AT_type` that the typedef refers to. rdar://137499401 (cherry picked from commit 1f35b52)

Michael137 requested review from OCHyams and dwblaikie December 1, 2025 13:31

Michael137 requested a review from JDevlieghere as a code owner December 1, 2025 13:31

llvmbot added the lldb label Dec 1, 2025

Michael137 force-pushed the lldb/template-alias-basic branch from 7c23175 to 83792f3 Compare December 1, 2025 13:32

Michael137 force-pushed the lldb/template-alias-basic branch from 2aa6433 to 3401bc5 Compare December 2, 2025 07:04

adrian-prantl approved these changes Dec 3, 2025

View reviewed changes

Michael137 added 4 commits December 3, 2025 11:00

fixup! clang-format

2c68458

fixup! elaborate on test comment

50c73e8

Michael137 force-pushed the lldb/template-alias-basic branch from 684ee3c to 50c73e8 Compare December 3, 2025 02:01

Michael137 enabled auto-merge (squash) December 3, 2025 02:01

Michael137 disabled auto-merge December 3, 2025 03:06

Michael137 merged commit 1f35b52 into llvm:main Dec 3, 2025
12 of 14 checks passed

Michael137 deleted the lldb/template-alias-basic branch December 3, 2025 03:07

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[lldb][DWARFASTParserClang] Treat DW_TAG_template_alias like we do DW_TAG_typedef #170135

[lldb][DWARFASTParserClang] Treat DW_TAG_template_alias like we do DW_TAG_typedef #170135

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[lldb][DWARFASTParserClang] Treat DW_TAG_template_alias like we do DW_TAG_typedef #170135

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