[lldb/DWARF] Follow DW_AT_signature when computing type contexts (#93675)

This is necessary to correctly resolve the context within types, as the
name of the type is only present in the type unit.

Author: labath

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

@@ -16,6 +16,7 @@
 #include "lldb/Symbol/Type.h"
 
 #include "llvm/ADT/iterator.h"
+#include "llvm/BinaryFormat/Dwarf.h"
 
 using namespace lldb_private;
 using namespace lldb_private::dwarf;
@@ -390,6 +391,11 @@ static void GetDeclContextImpl(DWARFDIE die,
       die = spec;
       continue;
     }
+    // To find the name of a type in a type unit, we must follow the signature.
+    if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_signature)) {
+      die = spec;
+      continue;
+    }
 
     // Add this DIE's contribution at the end of the chain.
     auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
@@ -444,6 +450,12 @@ static void GetTypeLookupContextImpl(DWARFDIE die,
                                      std::vector<CompilerContext> &context) {
   // Stop if we hit a cycle.
   while (die && seen.insert(die.GetID()).second) {
+    // To find the name of a type in a type unit, we must follow the signature.
+    if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_signature)) {
+      die = spec;
+      continue;
+    }
+
     // If there is no name, then there is no need to look anything up for this
     // DIE.
     const char *name = die.GetName();

lldb/test/Shell/SymbolFile/DWARF/x86/Inputs/debug-types-basic.cpp

@@ -10,6 +10,15 @@ struct A {
   EC ec;
 };
 
+struct Outer {
+  int i;
+  struct Inner {
+    long l;
+  };
+};
+
 extern constexpr A a{42, 47l, 4.2f, 4.7, e1, EC::e3};
 extern constexpr E e(e2);
 extern constexpr EC ec(EC::e2);
+extern constexpr Outer outer{47};
+extern constexpr Outer::Inner outer_inner{42l};

lldb/test/Shell/SymbolFile/DWARF/x86/debug-types-basic.test

@@ -51,6 +51,12 @@ type lookup EC
 # CHECK-NEXT:   e3
 # CHECK-NEXT: }
 
+type lookup Outer::Inner
+# CHECK-LABEL: type lookup Outer::Inner
+# CHECK:      struct Inner {
+# CHECK-NEXT:   long l;
+# CHECK-NEXT: }
+
 expression (E) 1
 # CHECK-LABEL: expression (E) 1
 # CHECK: (E) $0 = e2
@@ -59,8 +65,9 @@ expression (EC) 1
 # CHECK-LABEL: expression (EC) 1
 # CHECK: (EC) $1 = e2
 
-target variable a e ec
+target variable a e ec outer_inner
 # CHECK-LABEL: target variable a e ec
 # CHECK: (const A) a = (i = 42, l = 47, f = 4.{{[12].*}}, d = 4.{{[67].*}}, e = e1, ec = e3)
 # CHECK: (const E) e = e2
 # CHECK: (const EC) ec = e2
+# CHECK: (const Outer::Inner) outer_inner = (l = 42)