ArrayTypeTraitExpr - question about serialization

Hi all,

While implementing AST import from PCH file (-ast-dump), I stepped on an issue with ArrayTypeTraitExpr serialization. When ArrayTypeTraitExpr is being serialized, its sub-expr (dimension expression) doesn’t got serialized.

So the question is: should we serialize ArrayTypeTraitExpr::Dimension? And, if yes, are ASTImporter tests a good place for test case (the fix itself is pretty simple)? The issue is that I tried to import dimension expression which was never initialized in PCH.

The another question is: how full the serialization should be? Should we always serialize all the parts of AST nodes or just some meaningful?