[lldb/DWARF] Search fallback to the manual index in GetFullyQualified… (#102123)

…Type

This is needed to ensure we find a type if its definition is in a CU
that wasn't indexed. This can happen if the definition is in some
precompiled code (e.g. the c++ standard library) which was built with
different flags than the rest of the binary.

Author: labath

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

@@ -371,6 +371,7 @@ void DebugNamesDWARFIndex::GetFullyQualifiedType(
         !ProcessEntry(entry, callback))
       return;
   }
+  m_fallback.GetFullyQualifiedType(context, callback);
 }
 
 bool DebugNamesDWARFIndex::SameParentChain(

lldb/test/Shell/SymbolFile/DWARF/x86/mixed-debug-names-complete-type-search.test

@@ -0,0 +1,35 @@
+REQUIRES: lld, python
+
+RUN: split-file %s %t
+RUN: %clang --target=x86_64-pc-linux -g -gpubnames -c %t/file1.c -o %t-1.o
+RUN: %clang --target=x86_64-pc-linux -g -gno-pubnames -c %t/file2.c -o %t-2.o
+RUN: llvm-dwarfdump %t-1.o --debug-names | FileCheck %s --check-prefix=PUBNAMES
+RUN: llvm-dwarfdump %t-2.o --debug-names | FileCheck %s --check-prefix=NOPUBNAMES
+RUN: ld.lld %t-1.o %t-2.o -o %t.out
+RUN: %lldb %t.out -s %t/commands -o exit | FileCheck %s
+
+// Precondition check: The first file should contain a debug_names index, but no
+// entries for MYSTRUCT.
+PUBNAMES: Name Index @ 0x0 {
+PUBNAMES-NOT: MYSTRUCT
+
+// The second file should not contain an index.
+NOPUBNAMES-NOT: Name Index
+
+// Starting from the variable in the first file, we should be able to find the
+// declaration of the type in the first unit, and then match that with the
+// definition in the second unit.
+CHECK:      (lldb) script
+CHECK:      struct MYSTRUCT {
+CHECK-NEXT:   int x;
+CHECK-NEXT: }
+
+#--- commands
+script lldb.target.FindFirstGlobalVariable("struct_ptr").GetType().GetPointeeType()
+#--- file1.c
+struct MYSTRUCT *struct_ptr;
+#--- file2.c
+struct MYSTRUCT {
+  int x;
+};
+struct MYSTRUCT struct_;