Since only mutable types and attributes can go into infinite recursion
inside SubElementInterface::walkSubElement, and there are only a few of
them (mutable types and attributes), we introduce new traits for Type
and Attribute: TypeTrait::IsMutable and AttributeTrait::IsMutable,
respectively. They indicate whether a type or attribute is mutable.
Such traits are required if the ImplType defines a `mutate` function.
Then, inside SubElementInterface, we use a set to record visited mutable
types and attributes that have been visited before.
Differential Revision: https://reviews.llvm.org/D127537
These interfaces allow for a composite attribute or type to opaquely provide access to any held attributes or types. There are several intended use cases for this interface. The first of which is to allow the printer to create aliases for non-builtin dialect attributes and types. In the future, this interface will also be extended to allow for SymbolRefAttr to be placed on other entities aside from just DictionaryAttr and ArrayAttr.
To limit potential test breakages, this revision only adds the new interfaces to the builtin attributes/types that are currently hardcoded during AsmPrinter alias generation. In a followup the remaining builtin attributes/types, and non-builtin attributes/types can be extended to support it.
Differential Revision: https://reviews.llvm.org/D102945
