[WIP][lldb] Use forward decls with redeclared definitions instead of minimal import for records

lldb/source/Plugins/ExpressionParser/Clang/ASTUtils.h

@@ -10,6 +10,8 @@
 #define LLDB_SOURCE_PLUGINS_EXPRESSIONPARSER_CLANG_ASTUTILS_H
 
 #include "clang/Basic/ASTSourceDescriptor.h"
+#include "Plugins/TypeSystem/Clang/ImporterBackedASTSource.h"
+#include "clang/Basic/Module.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/MultiplexExternalSemaSource.h"
 #include "clang/Sema/Sema.h"
@@ -26,7 +28,7 @@ namespace lldb_private {
 
 /// Wraps an ExternalASTSource into an ExternalSemaSource. Doesn't take
 /// ownership of the provided source.
-class ExternalASTSourceWrapper : public clang::ExternalSemaSource {
+class ExternalASTSourceWrapper : public ImporterBackedASTSource {
   ExternalASTSource *m_Source;
 
 public:
@@ -246,7 +248,7 @@ class ASTConsumerForwarder : public clang::SemaConsumer {
 /// provide more accurate replies to the requests, but might not be able to
 /// answer all requests. The debug information will be used as a fallback then
 /// to provide information that is not in the C++ module.
-class SemaSourceWithPriorities : public clang::ExternalSemaSource {
+class SemaSourceWithPriorities : public ImporterBackedASTSource {
 
 private:
   /// The sources ordered in decreasing priority.
@@ -279,9 +281,16 @@ class SemaSourceWithPriorities : public clang::ExternalSemaSource {
     return nullptr;
   }
 
+  /// Call ExternalASTSource::CompleteRedeclChain(D)
+  /// on each AST source. Returns as soon as we got
+  /// a definition for D.
   void CompleteRedeclChain(const clang::Decl *D) override {
-    for (size_t i = 0; i < Sources.size(); ++i)
+    for (size_t i = 0; i < Sources.size(); ++i) {
       Sources[i]->CompleteRedeclChain(D);
+      if (auto *td = llvm::dyn_cast<clang::TagDecl>(D))
+        if (td->getDefinition())
+          return;
+    }
   }
 
   clang::Selector GetExternalSelector(uint32_t ID) override {