Annotation of implements is not properly type-checked

[trocher]

Version Information

• vyper Version (output of vyper --version): 0.3.8+commit.7ff8f307
• OS: OSX
• Python Version (output of python --version): 3.8.0

What's your issue about?

At the moment, visit_ImplementsDecl relies on the fact that the object mapped to node.annotation.id in the namespace defines a method validate_implements to ensure that the given name corresponds to an interface.

vyper/vyper/semantics/analysis/module.py

Lines 157 to 161 in 0a64906

	def visit_ImplementsDecl(self, node):
	interface_name = node.annotation.id
	other_iface = self.namespace[interface_name]
	other_iface.validate_implements(node)

It would probably be better to use type_from_annotation:

  def visit_ImplementsDecl(self, node):
      interface_name = node.annotation

      other_iface = type_from_annotation(interface_name)

      # Add a check to ensure that: isinstance(other_iface,InterfaceT)

      other_iface.validate_implements(node)

This would also have the advantage to give better error messages for the 2 following cases:

• When a constant is given (currently the following is given AttributeError: 'Int' object has no attribute 'id'
• When a type or more generally an identifier which is not an interface is given (currently for example: AttributeError: 'StructT' object has no attribute 'validate_implements')