[LLDB][NativePDB] Use undecorated name for types if UniqueName isn't mangled (#152114)

Languages other than C/C++ don't necessarily emit mangled names in the
`UniqueName` field of type records. Rust specifically emits a unique ID
that doesn't contain the name.

For example, `(i32, i32)` is emitted as

```llvm
!266 = !DICompositeType(
  tag: DW_TAG_structure_type, name: "tuple$<i32,i32>", file: !9, size: 64, align: 32,
  elements: !267, templateParams: !17, identifier: "19122721b0632fe96c0dd37477674472"
)
```

which results in

```
  0x1091 | LF_STRUCTURE [size = 72, hash = 0x1AC67] `tuple$<i32,i32>`
           unique name: `19122721b0632fe96c0dd37477674472`
           vtable: <no type>, base list: <no type>, field list: 0x1090
           options: has unique name, sizeof 8
```

In C++ with Clang and MSVC, a structure similar to this would result in
```
   0x136F | LF_STRUCTURE [size = 44, hash = 0x30BE2] `MyTuple`
            unique name: `.?AUMyTuple@@`
            vtable: <no type>, base list: <no type>, field list: 0x136E
            options: has unique name, sizeof 8
```

With this PR, if a `UniqueName` is encountered that couldn't be parsed,
it will fall back to using the undecorated (→ do the same as if the
unique name is empty/unavailable).

I'm not sure how to test this. Maybe compiling the LLVM IR that rustc
emits?

Fixes #152051.

Author: Nerixyz

lldb/source/Plugins/SymbolFile/NativePDB/PdbAstBuilder.cpp

@@ -178,7 +178,7 @@ PdbAstBuilder::CreateDeclInfoForType(const TagRecord &record, TypeIndex ti) {
   std::string_view sv(record.UniqueName.begin(), record.UniqueName.size());
   llvm::ms_demangle::TagTypeNode *ttn = demangler.parseTagUniqueName(sv);
   if (demangler.Error)
-    return {m_clang.GetTranslationUnitDecl(), std::string(record.UniqueName)};
+    return CreateDeclInfoForUndecoratedName(record.Name);
 
   llvm::ms_demangle::IdentifierNode *idn =
       ttn->QualifiedName->getUnqualifiedIdentifier();

lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp

@@ -622,18 +622,14 @@ lldb::TypeSP SymbolFileNativePDB::CreateSimpleType(TypeIndex ti,
 }
 
 static std::string GetUnqualifiedTypeName(const TagRecord &record) {
-  if (!record.hasUniqueName()) {
-    MSVCUndecoratedNameParser parser(record.Name);
-    llvm::ArrayRef<MSVCUndecoratedNameSpecifier> specs = parser.GetSpecifiers();
-
-    return std::string(specs.back().GetBaseName());
-  }
+  if (!record.hasUniqueName())
+    return std::string(MSVCUndecoratedNameParser::DropScope(record.Name));
 
   llvm::ms_demangle::Demangler demangler;
   std::string_view sv(record.UniqueName.begin(), record.UniqueName.size());
   llvm::ms_demangle::TagTypeNode *ttn = demangler.parseTagUniqueName(sv);
   if (demangler.Error)
-    return std::string(record.Name);
+    return std::string(MSVCUndecoratedNameParser::DropScope(record.Name));
 
   llvm::ms_demangle::IdentifierNode *idn =
       ttn->QualifiedName->getUnqualifiedIdentifier();

lldb/test/Shell/SymbolFile/NativePDB/rust-unique-name.ll

@@ -0,0 +1,85 @@
+; REQUIRES: system-windows
+; RUN: %build --compiler=clang-cl --nodefaultlib -o %t.exe -- %s
+; RUN: lldb-test symbols %t.exe | FileCheck %s
+
+; Output from
+; rustc lib.rs -C debuginfo=2 --emit=llvm-ir --crate-type=rlib
+; (using rlib to avoid including panic handlers in IR)
+;
+; lib.rs:
+;
+; #![no_std]
+; mod my_module {
+;     #[repr(C)]
+;     pub struct MyStruct {
+;         pub a: i32,
+;         pub b: i32,
+;     }
+; }
+; #[unsafe(no_mangle)]
+; extern "C" fn mainCRTStartup() -> my_module::MyStruct {
+;     my_module::MyStruct { a: 3, b: 4 }
+; }
+; #[unsafe(no_mangle)]
+; extern "C" fn main() {}
+
+; =======================================================================
+; ModuleID = 'lib.b43fc69277defcf4-cgu.0'
+source_filename = "lib.b43fc69277defcf4-cgu.0"
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; Function Attrs: nounwind uwtable
+define i64 @mainCRTStartup() unnamed_addr #0 !dbg !6 {
+start:
+  %_0 = alloca [8 x i8], align 4
+  store i32 3, ptr %_0, align 4, !dbg !20
+  %0 = getelementptr inbounds i8, ptr %_0, i64 4, !dbg !20
+  store i32 4, ptr %0, align 4, !dbg !20
+  %1 = load i64, ptr %_0, align 4, !dbg !21
+  ret i64 %1, !dbg !21
+}
+
+; Function Attrs: nounwind uwtable
+define void @main() unnamed_addr #0 !dbg !22 {
+start:
+  ret void, !dbg !25
+}
+
+attributes #0 = { nounwind uwtable "target-cpu"="x86-64" "target-features"="+cx16,+sse3,+sahf" }
+
+!llvm.module.flags = !{!0, !1, !2}
+!llvm.ident = !{!3}
+!llvm.dbg.cu = !{!4}
+
+!0 = !{i32 8, !"PIC Level", i32 2}
+!1 = !{i32 2, !"CodeView", i32 1}
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !{!"rustc version 1.88.0 (6b00bc388 2025-06-23)"}
+!4 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !5, producer: "clang LLVM (rustc version 1.88.0 (6b00bc388 2025-06-23))", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false)
+!5 = !DIFile(filename: "src/lib.rs\\@\\lib.b43fc69277defcf4-cgu.0", directory: "F:\\Dev\\testing")
+!6 = distinct !DISubprogram(name: "mainCRTStartup", scope: !8, file: !7, line: 12, type: !9, scopeLine: 12, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !4, templateParams: !19)
+!7 = !DIFile(filename: "src/lib.rs", directory: "F:\\Dev\\testing", checksumkind: CSK_SHA256, checksum: "586087c038922a8fa0183c4b20c075445761d545e02d06af80cd5a62dcadb3ec")
+!8 = !DINamespace(name: "lib", scope: null)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11}
+!11 = !DICompositeType(tag: DW_TAG_structure_type, name: "MyStruct", scope: !13, file: !12, size: 64, align: 32, flags: DIFlagPublic, elements: !14, templateParams: !19, identifier: "99a3f33b03974e4eaf7224f807a544bf")
+!12 = !DIFile(filename: "<unknown>", directory: "")
+!13 = !DINamespace(name: "my_module", scope: !8)
+!14 = !{!15, !18}
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !11, file: !12, baseType: !16, size: 32, align: 32, flags: DIFlagPublic)
+!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "i32", file: !12, baseType: !17)
+!17 = !DIBasicType(name: "__int32", size: 32, encoding: DW_ATE_signed)
+!18 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !11, file: !12, baseType: !16, size: 32, align: 32, offset: 32, flags: DIFlagPublic)
+!19 = !{}
+!20 = !DILocation(line: 13, scope: !6)
+!21 = !DILocation(line: 14, scope: !6)
+!22 = distinct !DISubprogram(name: "main", scope: !8, file: !7, line: 17, type: !23, scopeLine: 17, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !4, templateParams: !19)
+!23 = !DISubroutineType(types: !24)
+!24 = !{null}
+!25 = !DILocation(line: 17, scope: !22)
+
+; CHECK:      Type{{.*}} , name = "MyStruct", size = 8, compiler_type = {{.*}} struct MyStruct {
+; CHECK-NEXT:         int a;
+; CHECK-NEXT:         int b;
+; CHECK-NEXT:     }

lldb/test/Shell/lit.cfg.py

@@ -25,7 +25,7 @@
 
 # suffixes: A list of file extensions to treat as test files. This is overriden
 # by individual lit.local.cfg files in the test subdirectories.
-config.suffixes = [".test", ".cpp", ".s", ".m"]
+config.suffixes = [".test", ".cpp", ".s", ".m", ".ll"]
 
 # excludes: A list of directories to exclude from the testsuite. The 'Inputs'
 # subdirectories contain auxiliary inputs for various tests in their parent