[lldb][NFC] Make metadata tracking type safe

Summary:
LLDB associates additional information with Types and Declarations which it calls ClangASTMetadata.
ClangASTMetadata is stored by the ClangASTSourceCommon which is implemented by having a large map of
`void *` keys to associated `ClangASTMetadata` values. To make this whole mechanism even unsafer
we also decided to use `clang::Decl *` as one of pointers we throw in there (beside `clang::Type *`).

The Decl class hierarchy uses multiple inheritance which means that not all pointers have the
same address when they are implicitly converted to pointers of their parent classes. For example
`clang::Decl *` and `clang::DeclContext *` won't end up being the same address when they
are implicitly converted from one of the many Decl-subclasses that inherit from both.

As we use the addresses as the keys in our Metadata map, this means that any implicit type
conversions to parent classes (or anything else that changes the addresses) will break our metadata tracking
in obscure ways.

Just to illustrate how broken this whole mechanism currently is:
```lang=cpp
  // m_ast is our ClangASTContext. Let's double check that from GetTranslationUnitDecl
  // in ClangASTContext and ASTContext return the same thing (one method just calls the other).
  assert(m_ast->GetTranslationUnitDecl() == m_ast->getASTContext()->getTranslationUnitDecl());
  // Ok, both methods have the same TU*. Let's store metadata with the result of one method call.
  m_ast->SetMetadataAsUserID(m_ast->GetTranslationUnitDecl(), 1234U);
  // Retrieve the same Metadata for the TU by using the TU* from the other method... which fails?
  EXPECT_EQ(m_ast->GetMetadata(m_ast->getASTContext()->getTranslationUnitDecl())->GetUserID(), 1234U);
  // Turns out that getTranslationUnitDecl one time returns a TranslationUnitDecl* but the other time
  // we return one of the parent classes of TranslationUnitDecl (DeclContext).
```

This patch splits up the `void *` API into two where one does the `clang::Type *` tracking and one the `clang::Decl *` mapping.
Type and Decl are disjoint class hierarchies so there is no implicit conversion possible that could influence
the address values.

I had to change the storing of `clang::QualType` opaque pointers to their `clang::Type *` equivalents as
opaque pointers are already `void *` pointers to begin with. We don't seem to ever set any qualifier in any of these
QualTypes to this conversion should be NFC.

Reviewers: labath, shafik, aprantl

Reviewed By: labath

Subscribers: JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D71409

2 files changed, 48 insertions, 17 deletions

diff --git a/lldb/source/Symbol/ClangASTContext.cpp b/lldb/source/Symbol/ClangASTContext.cpp
index 33fdee0dad7..2576a372076 100644
--- a/lldb/source/Symbol/ClangASTContext.cpp
+++ b/lldb/source/Symbol/ClangASTContext.cpp
@@ -2398,14 +2398,31 @@ bool ClangASTContext::GetCompleteDecl(clang::ASTContext *ast,
   }
 }
 
-void ClangASTContext::SetMetadataAsUserID(const void *object,
+void ClangASTContext::SetMetadataAsUserID(const clang::Decl *decl,
                                           user_id_t user_id) {
   ClangASTMetadata meta_data;
   meta_data.SetUserID(user_id);
-  SetMetadata(object, meta_data);
+  SetMetadata(decl, meta_data);
 }
 
-void ClangASTContext::SetMetadata(const void *object,
+void ClangASTContext::SetMetadataAsUserID(const clang::Type *type,
+                                          user_id_t user_id) {
+  ClangASTMetadata meta_data;
+  meta_data.SetUserID(user_id);
+  SetMetadata(type, meta_data);
+}
+
+void ClangASTContext::SetMetadata(const clang::Decl *object,
+                                  ClangASTMetadata &metadata) {
+  ClangExternalASTSourceCommon *external_source =
+      ClangExternalASTSourceCommon::Lookup(
+          getASTContext()->getExternalSource());
+
+  if (external_source)
+    external_source->SetMetadata(object, metadata);
+}
+
+void ClangASTContext::SetMetadata(const clang::Type *object,
                                   ClangASTMetadata &metadata) {
   ClangExternalASTSourceCommon *external_source =
       ClangExternalASTSourceCommon::Lookup(
@@ -2416,14 +2433,23 @@ void ClangASTContext::SetMetadata(const void *object,
 }
 
 ClangASTMetadata *ClangASTContext::GetMetadata(clang::ASTContext *ast,
-                                               const void *object) {
+                                               const clang::Decl *object) {
   ClangExternalASTSourceCommon *external_source =
       ClangExternalASTSourceCommon::Lookup(ast->getExternalSource());
 
   if (external_source)
     return external_source->GetMetadata(object);
-  else
-    return nullptr;
+  return nullptr;
+}
+
+ClangASTMetadata *ClangASTContext::GetMetadata(clang::ASTContext *ast,
+                                               const clang::Type *object) {
+  ClangExternalASTSourceCommon *external_source =
+      ClangExternalASTSourceCommon::Lookup(ast->getExternalSource());
+
+  if (external_source)
+    return external_source->GetMetadata(object);
+  return nullptr;
 }
 
 bool ClangASTContext::SetTagTypeKind(clang::QualType tag_qual_type,
@@ -5096,7 +5122,7 @@ GetDynamicArrayInfo(ClangASTContext &ast, SymbolFile *sym_file,
                     clang::QualType qual_type,
                     const ExecutionContext *exe_ctx) {
   if (qual_type->isIncompleteArrayType())
-    if (auto *metadata = ast.GetMetadata(qual_type.getAsOpaquePtr()))
+    if (auto *metadata = ast.GetMetadata(qual_type.getTypePtr()))
       return sym_file->GetDynamicArrayInfoForUID(metadata->GetUserID(),
                                                  exe_ctx);
   return llvm::None;
@@ -8856,8 +8882,11 @@ void ClangASTContext::DumpSummary(lldb::opaque_compiler_type_t type,
 void ClangASTContext::DumpTypeDescription(lldb::opaque_compiler_type_t type) {
   StreamFile s(stdout, false);
   DumpTypeDescription(type, &s);
+
+  CompilerType ct(this, type);
+  const clang::Type *clang_type = ClangUtil::GetQualType(ct).getTypePtr();
   ClangASTMetadata *metadata =
-      ClangASTContext::GetMetadata(getASTContext(), type);
+      ClangASTContext::GetMetadata(getASTContext(), clang_type);
   if (metadata) {
     metadata->Dump(&s);
   }
@@ -9485,7 +9514,7 @@ ClangASTContext::DeclContextGetAsNamespaceDecl(const CompilerDeclContext &dc) {
 
 ClangASTMetadata *
 ClangASTContext::DeclContextGetMetaData(const CompilerDeclContext &dc,
-                                        const void *object) {
+                                        const Decl *object) {
   clang::ASTContext *ast = DeclContextGetClangASTContext(dc);
   if (ast)
     return ClangASTContext::GetMetadata(ast, object);
diff --git a/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp b/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp
index b60b3791aae..66fb4f3b3f0 100644
--- a/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp
+++ b/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp
@@ -52,17 +52,19 @@ ClangExternalASTSourceCommon::~ClangExternalASTSourceCommon() {
 }
 
 ClangASTMetadata *
-ClangExternalASTSourceCommon::GetMetadata(const void *object) {
-  auto It = m_metadata.find(object);
-  if (It != m_metadata.end())
+ClangExternalASTSourceCommon::GetMetadata(const clang::Decl *object) {
+  auto It = m_decl_metadata.find(object);
+  if (It != m_decl_metadata.end())
     return &It->second;
-  else
-    return nullptr;
+  return nullptr;
 }
 
-void ClangExternalASTSourceCommon::SetMetadata(const void *object,
-                                               ClangASTMetadata &metadata) {
-  m_metadata[object] = metadata;
+ClangASTMetadata *
+ClangExternalASTSourceCommon::GetMetadata(const clang::Type *object) {
+  auto It = m_type_metadata.find(object);
+  if (It != m_type_metadata.end())
+    return &It->second;
+  return nullptr;
 }
 
 void ClangASTMetadata::Dump(Stream *s) {