[lldb][SymbolFileDWARF] Share GetDIEToType between SymbolFiles of a SymbolFileDWARFDebugMap (#120569)

The problem here manifests as follows:
1. We are stopped in main.o, so the first `ParseTypeFromDWARF` on
`FooImpl<char>` gets called on `main.o`'s SymbolFile. This adds a
mapping from *declaration die* -> `TypeSP` into `main.o`'s
`GetDIEToType` map.
2. We then `CompleteType(FooImpl<char>)`. Depending on the order of
entries in the debug-map, this might call `CompleteType` on `lib.o`'s
SymbolFile. In which case, `GetDIEToType().lookup(decl_die)` will return
a `nullptr`. This is already a bit iffy because some of the surrounding
code assumes we don't call `CompleteTypeFromDWARF` with a `nullptr`
`Type*`. E.g., `CompleteEnumType` blindly dereferences it (though enums
will never encounter this because their definition is fetched in
ParseEnum, unlike for structures).
3. While in `CompleteTypeFromDWARF`, we call `ParseTypeFromDWARF` again.
This will parse the member function `FooImpl::Create` and its return
type which is a typedef to `FooImpl*`. But now we're inside `lib.o`'s
SymbolFile, so we call it on the definition DIE. In step (2) we just
inserted a `nullptr` into `GetDIEToType` for the definition DIE, so we
trivially return a `nullptr` from `ParseTypeFromDWARF`. Instead of
reporting back this parse failure to the user LLDB trucks on and marks
`FooImpl::Ref` to be `void*`.

This test-case will trigger an assert in `TypeSystemClang::VerifyDecl`
even if we just `frame var` (but only in debug-builds). In release
builds where this function is a no-op, we'll create an incorrect Clang
AST node for the `Ref` typedef.

The proposed fix here is to share the `GetDIEToType` map between
SymbolFiles if a debug-map exists.

**Alternatives considered**
* Check the `GetDIEToType` map of the `SymbolFile` that the declaration
DIE belongs to. The assumption here being that if we called
`ParseTypeFromDWARF` on a declaration, the `GetDIEToType` map that the
result was inserted into was the one on that DIE's SymbolFile. This was
the first version of this patch, but that felt like a weaker version
sharing the map. It complicates the code in `CompleteType` and is less
consistent with the other bookkeeping structures we already share
between SymbolFiles
* Return from `SymbolFileDWARF::CompleteType` if there is no type in the
current `GetDIEToType`. Then `SymbolFileDWARFDebugMap::CompleteType`
could continue to the next `SymbolFile` which does own the type. But
that didn't quite work because we remove the
`GetForwardCompilerTypeToDie` entry in `SymbolFile::CompleteType`, which
`SymbolFileDWARFDebugMap::CompleteType` relies upon for iterating

Author: Michael137

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

@@ -3633,8 +3633,7 @@ bool DWARFASTParserClang::CopyUniqueClassMethodTypes(
       static_cast<DWARFASTParserClang *>(
           SymbolFileDWARF::GetDWARFParser(*dst_class_die.GetCU()));
   auto link = [&](DWARFDIE src, DWARFDIE dst) {
-    SymbolFileDWARF::DIEToTypePtr &die_to_type =
-        dst_class_die.GetDWARF()->GetDIEToType();
+    auto &die_to_type = dst_class_die.GetDWARF()->GetDIEToType();
     clang::DeclContext *dst_decl_ctx =
         dst_dwarf_ast_parser->m_die_to_decl_ctx[dst.GetDIE()];
     if (dst_decl_ctx)

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

@@ -482,6 +482,13 @@ static ConstString GetDWARFMachOSegmentName() {
   return g_dwarf_section_name;
 }
 
+llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &
+SymbolFileDWARF::GetDIEToType() {
+  if (SymbolFileDWARFDebugMap *debug_map_symfile = GetDebugMapSymfile())
+    return debug_map_symfile->GetDIEToType();
+  return m_die_to_type;
+}
+
 llvm::DenseMap<lldb::opaque_compiler_type_t, DIERef> &
 SymbolFileDWARF::GetForwardDeclCompilerTypeToDIE() {
   if (SymbolFileDWARFDebugMap *debug_map_symfile = GetDebugMapSymfile())
@@ -1594,6 +1601,8 @@ bool SymbolFileDWARF::CompleteType(CompilerType &compiler_type) {
   if (!dwarf_ast)
     return false;
   Type *type = GetDIEToType().lookup(decl_die.GetDIE());
+  assert(type);
+
   if (decl_die != def_die) {
     GetDIEToType()[def_die.GetDIE()] = type;
     DWARFASTParserClang *ast_parser =

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h

@@ -335,9 +335,7 @@ class SymbolFileDWARF : public SymbolFileCommon {
     m_file_index = file_index;
   }
 
-  typedef llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> DIEToTypePtr;
-
-  virtual DIEToTypePtr &GetDIEToType() { return m_die_to_type; }
+  virtual llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &GetDIEToType();
 
   virtual llvm::DenseMap<lldb::opaque_compiler_type_t, DIERef> &
   GetForwardDeclCompilerTypeToDIE();
@@ -529,7 +527,7 @@ class SymbolFileDWARF : public SymbolFileCommon {
   UniqueDWARFASTTypeMap m_unique_ast_type_map;
   // A map from DIE to lldb_private::Type. For record type, the key might be
   // either declaration DIE or definition DIE.
-  DIEToTypePtr m_die_to_type;
+  llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> m_die_to_type;
   DIEToVariableSP m_die_to_variable_sp;
   // A map from CompilerType to the struct/class/union/enum DIE (might be a
   // declaration or a definition) that is used to construct it.

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.h

@@ -291,6 +291,10 @@ class SymbolFileDWARFDebugMap : public SymbolFileCommon {
     return m_unique_ast_type_map;
   }
 
+  llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &GetDIEToType() {
+    return m_die_to_type;
+  }
+
   // OSOEntry
   class OSOEntry {
   public:
@@ -329,6 +333,8 @@ class SymbolFileDWARFDebugMap : public SymbolFileCommon {
   llvm::DenseMap<lldb::opaque_compiler_type_t, DIERef>
       m_forward_decl_compiler_type_to_die;
   UniqueDWARFASTTypeMap m_unique_ast_type_map;
+  llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> m_die_to_type;
+
   DebugMap m_debug_map;
 
   // When an object file from the debug map gets parsed in

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

@@ -102,7 +102,8 @@ bool SymbolFileDWARFDwo::ParseVendorDWARFOpcode(
   return GetBaseSymbolFile().ParseVendorDWARFOpcode(op, opcodes, offset, stack);
 }
 
-SymbolFileDWARF::DIEToTypePtr &SymbolFileDWARFDwo::GetDIEToType() {
+llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &
+SymbolFileDWARFDwo::GetDIEToType() {
   return GetBaseSymbolFile().GetDIEToType();
 }
 

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDwo.h

@@ -70,7 +70,7 @@ class SymbolFileDWARFDwo : public SymbolFileDWARF {
   SymbolFileDWARF *GetDIERefSymbolFile(const DIERef &die_ref) override;
 
 protected:
-  DIEToTypePtr &GetDIEToType() override;
+  llvm::DenseMap<const DWARFDebugInfoEntry *, Type *> &GetDIEToType() override;
 
   DIEToVariableSP &GetDIEToVariable() override;
 

lldb/test/API/lang/cpp/typedef-to-outer-fwd/Makefile

@@ -0,0 +1,3 @@
+CXX_SOURCES := lib.cpp main.cpp
+
+include Makefile.rules

lldb/test/API/lang/cpp/typedef-to-outer-fwd/TestTypedefToOuterFwd.py

@@ -0,0 +1,38 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCaseTypedefToOuterFwd(TestBase):
+    """
+    We find a global variable whose type is forward declared
+    (whose definition is in either main.o or lib.o). We then
+    try to get the 'Ref' typedef nested within that forward
+    declared type. This test makes sure we correctly resolve
+    this typedef.
+
+    We test this for two cases, where the definition lives
+    in main.o or lib.o.
+    """
+
+    def check_global_var(self, target, name: str):
+        var = target.FindFirstGlobalVariable(name)
+        self.assertSuccess(var.GetError(), f"Found {name}")
+
+        var_type = var.GetType()
+        self.assertTrue(var_type)
+
+        impl = var_type.GetPointeeType()
+        self.assertTrue(impl)
+
+        ref = impl.FindDirectNestedType("Ref")
+        self.assertTrue(ref)
+
+        self.assertEqual(ref.GetCanonicalType(), var_type)
+
+    def test(self):
+        self.build()
+        target = self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+        self.check_global_var(target, "gLibExternalDef")
+        self.check_global_var(target, "gMainExternalDef")

lldb/test/API/lang/cpp/typedef-to-outer-fwd/lib.cpp

@@ -0,0 +1,10 @@
+#include "lib.h"
+
+template <typename T> struct FooImpl {
+  using Ref = FooImpl<T> *;
+
+  Ref Create() { return new FooImpl<T>(); }
+};
+
+FooImpl<char> gLibLocalDef;
+BarImpl<char> *gLibExternalDef = nullptr;

lldb/test/API/lang/cpp/typedef-to-outer-fwd/lib.h

@@ -0,0 +1,7 @@
+#ifndef LIB_H_IN
+#define LIB_H_IN
+
+template <typename T> struct FooImpl;
+template <typename T> struct BarImpl;
+
+#endif // LIB_H_IN