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

Depends on: * #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.

Author: Michael137

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:

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"
 
@@ -1882,3 +1883,102 @@ TEST_F(DWARFASTParserClangTests, TestBitIntParsing) {
  EXPECT_EQ(type_sp->GetForwardCompilerType().GetTypeName(), "_BitInt(64)");
  }
 }
+
+TEST_F(DWARFASTParserClangTests, TestTemplateAlias_NoSimpleTemplateNames) {
+ // Tests that we correctly parse the DW_TAG_template_alias generated by
+ // -gno-simple-template-names.
+
+ const char *yamldata = R"(
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_EXEC
+ Machine: EM_AARCH64
+DWARF:
+ debug_abbrev:
+ - ID: 0
+ Table:
+ - Code: 0x1
+ Tag: DW_TAG_compile_unit
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_language
+ Form: DW_FORM_data2
+ - Code: 0x2
+ Tag: DW_TAG_base_type
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_string
+ - Code: 0x3
+ Tag: DW_TAG_template_alias
+ Children: DW_CHILDREN_yes
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_string
+ - Attribute: DW_AT_type
+ Form: DW_FORM_ref4
+ - Code: 0x4
+ Tag: DW_TAG_template_type_parameter
+ Children: DW_CHILDREN_no
+ Attributes:
+ - Attribute: DW_AT_name
+ Form: DW_FORM_string
+ - Attribute: DW_AT_type
+ Form: DW_FORM_ref4
+
+ debug_info:
+ - Version: 5
+ UnitType: DW_UT_compile
+ AddrSize: 8
+ Entries:
+
+# DW_TAG_compile_unit
+# DW_AT_language (DW_LANG_C_plus_plus)
+
+ - AbbrCode: 0x1
+ Values:
+ - Value: 0x04
+
+# DW_TAG_base_type
+# DW_AT_name ('int')
+
+ - AbbrCode: 0x2
+ Values:
+ - CStr: int
+
+# DW_TAG_template_alias
+# DW_AT_name ('Foo<int>')
+# DW_AT_type ('int')
+# DW_TAG_template_type_parameter
+# DW_AT_name ('T')
+# DW_AT_type ('int')
+
+ - AbbrCode: 0x3
+ Values:
+ - CStr: Foo<int>
+ - Value: 0xf
+
+ - AbbrCode: 0x4
+ Values:
+ - CStr: T
+ - Value: 0xf
+...
+)";
+ DWARFASTParserClangYAMLTester tester(yamldata);
+ DWARFDIE cu_die = tester.GetCUDIE();
+
+ auto alias_die = cu_die.GetFirstChild().GetSibling();
+ ASSERT_TRUE(alias_die.IsValid());
+
+ SymbolContext sc;
+ auto type_sp =
+ tester.GetParser().ParseTypeFromDWARF(sc, alias_die,
+ /*type_is_new_ptr=*/nullptr);
+ ASSERT_NE(type_sp, nullptr);
+
+ EXPECT_TRUE(type_sp->IsTypedef());
+ EXPECT_EQ(type_sp->GetName(), "Foo<int>");
+ EXPECT_EQ(type_sp->GetForwardCompilerType().GetTypeName(), "Foo<int>");
+}