[PATCH] D86660: Modifying ImportDeclContext(...) to ensure that we also handle the case when the FieldDecl is an ArrayType whose ElementType is a RecordDecl

[Gabor Marton via Phabricator via cfe-commits]

martong added inline comments.


================
Comment at: clang/lib/AST/ASTImporter.cpp:1737
 
     // If we are in the process of ImportDefinition(...) for a RecordDecl we
     // want to make sure that we are also completing each FieldDecl. There
----------------
`ImportDefinition(...)` here refers to `ASTImporter::ImportDefinition(Decl*)` and not any of the `ASTNodeImporter::ImportDefinition` funcitons. This is a very important distinction, because the former is part of the public interface, while the latter are private implementation functions. Could you please fix this in the comment?


================
Comment at: clang/lib/AST/ASTImporter.cpp:1755-1759
+          QualType FromTy = ArrayFrom->getElementType();
+          QualType ToTy = ArrayTo->getElementType();
+
+          FromRecordDecl = FromTy->getAsRecordDecl();
+          ToRecordDecl = ToTy->getAsRecordDecl();
----------------
labath wrote:
> What about 2- or n-dimensional arrays?
@labath, this is a very good question! And made me realize that D71378 is fundamentally flawed (@shafik, please take no offense). Let me explain.

So, with D71378, we added the `if (ImportedOrErr) { ... }` block to import definitions specifically of fields' Record types. But we forget to handle arrays. Now we may forget to handle multidimensional arrays ... and we may forget to handle other language constructs. So, we would finally end up in re-implementing the logic of `ASTNodeImporter::VisitFieldDecl`.

So all this should have been handled properly by the preceding import call of the FieldDecl! Here
```
1735: ExpectedDecl ImportedOrErr = import(From);
```
I have a suspicion that real reason why this import call fails in case of the public ASTImporter::ImportDefinition() is that we fail to drive through the import kind (`IDK_Everything`) during the import process.
Below we set IDK_Everything and start a complete import process.
```
  8784   if (auto *ToRecord = dyn_cast<RecordDecl>(To)) {
  8785     if (!ToRecord->getDefinition()) {
  8786       return Importer.ImportDefinition(   // ASTNodeImporter::ImportDefinition !
  8787           cast<RecordDecl>(FromDC), ToRecord,
  8788           ASTNodeImporter::IDK_Everything);
  8789     }
  8790   }
```
However, there may be many places where we fail to channel through that we want to do a complete import. E.g here
```
1957           ImportDefinitionIfNeeded(Base1.getType()->getAsCXXRecordDecl()))
```
we do another definition import and IDK_Everything is not set. So we may have a wrong kind of import since the "minimal" flag is set.

The thing is, it is really confusing and error-prone to have both the `ASTImporter::Minimal` flag and the `ImportDefinitionKind`. They seem to be in contradiction to each other some times.
I think we should get rid of the Minimal flag. And Kind should be either a full completion (IDK_Everythink) or just a minimal (IDK_Basic). So, I'd scrap the IDK_Default too. Alternatively we could have a Kind member in AST**//Node//**Importer.
I think we should go into this direction to avoid similar problems during CodeGen in the future. WDYT?


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  https://reviews.llvm.org/D86660/new/

https://reviews.llvm.org/D86660